DOI: 10.1002/chem.201403243
Full Paper
& Asymmetric Catalysis
Stereoselective Hydrodehalogenation via a Radical-Based Mechanism Involving T-Shaped Chiral Nickel(I) Pincer Complexes Christoph Rettenmeier, Hubert Wadepohl, and Lutz H. Gade*[a] Dedicated to Professor Helmut Werner on the occasion of his 80th birthday
Abstract: We herein report the catalytic enantioselective hydrodehalogenation based on the interplay of a chiral molecular nickel(I)/nickel(II)hydride system. Prochiral geminal dihalogenides are dehalogenated via a secondary configurationally unstable, potentially metal-stabilized radical intermediate. In a subsequent step, the liberated radical is then trapped by the nickel(II) hydrido complex, present in a large excess under the catalytic conditions, which in turn induces the enantioselectivity during the hydrogen atom transfer
onto the radical intermediate. These new chiral nickel(I) complexes were found to catalyze the asymmetric hydrodehalogenation of geminal dihalogenides with moderate to good enantiomeric excess values using LiEt3BH as reductant. The main side product generally observed is the dehalogenated alkene, whereas the hydrodehalogenation of the chiral monohalogen compound occurred much more slowly despite the large excess of reductant.
Introduction Radical-based mechanistic pathways have been proposed both for nickel-catalyzed hydrodehalogenations and related CC coupling reactions.[1] For the latter, remarkable enantioselectivities have been achieved using chiral molecular catalysts.[2] On the other hand, whereas there have been a few attempts to achieve enantioselective hydrodehalogenation,[3] no example we are aware of employs a well-defined chiral molecular catalyst. A key question underlying the development of enantioselective hydrodehalogenation involving potential radical intermediates and multiple oxidation states of the metal concern the mechanism of stereo induction in such a transformation. Our approach is based on the partial hydrodehalogenation of prochiral geminal dihalides catalyzed by a molecular Ni catalyst. Two distinct molecular forms in different oxidation states interact with the substrate as well as the resulting reaction intermediate in subsequent steps of the catalytic transformation. Both nickel complexes contain the same chiral ligand, however, their role during the catalysis differs substantially: In a first step, the nickel(I) complex abstracts a halogen atom from the geminal dihalogenide, generating a nickel(II) chlorido complex and a configurationally labile radical species. The latter may be stabilized by a reversible coordination to the generated NiCl complex.[4] In a subsequent step, the liberated radical is then trapped by the nickel(II) hydrido complex, present in a large [a] C. Rettenmeier, Prof. Dr. H. Wadepohl, Prof. Dr. L. H. Gade Anorganisch-Chemisches Institut, Univeristt Heidelberg Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) E-mail: [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201403243. Chem. Eur. J. 2014, 20, 9657 – 9665
Scheme 1. Reactivity pattern observed for the hydrodehalogenation.
excess under the catalytic conditions, which in turn induces the enantioselectivity during the hydrogen atom transfer onto the radical intermediate (Scheme 1).
Results and Discussion We have previously reported the synthesis of the bisoxazolinmethylpyrrolido nickel chlorido complex 1 b and investigated its isomerization to the bis(oxazolinylmethylidene)pyrrolidinido complex 2 b (Scheme 2).[5] The rearrangement involves the planarization of the pincer ligand in which a conjugated 10-pelectron system strongly interacts with the metal center resulting in a significant stabilization. The latter has been found to be essential for the synthesis of a series of remarkably stable nickel(I) complexes[6, 7] by the reaction of the chlorido nickel complexes with LiEt3BH. The nickel hydrido complexes 3, which are initially formed, undergo H2 elimination to generate the T-shaped nickel(I) species 4 (Figure 1). K¼
9657
cðLigNiHÞ2 cðLigNiI Þ2 pðH2 Þ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper
Scheme 2. Synthesis of new nickel hydrido complexes 3 and nickel(I) complexes 4.
Figure 1. Second-order dependency on the concentration of 3 a for the rate of hydrogen elimination in 3 a at 273 K.
In solution the nickel(I) and nickel hydrido complexes are in a hydrogen pressure-dependent dynamic equilibrium (K = 12.4 bar1 at 295 K for 3 a/4 a, Scheme 2) with the rate of the NiIIH!NiI interconversion being of second order in hydrido complex concentration, which is consistent with a bimolecular mechanism (k = 5.31 104 L mol1 s1 at 273 K for 4 a; Figure 1). Single-crystal X-ray structure analyses of 3 a and 4 a established an almost perfectly planar ligand frame in a meridional coordination to the nickel center with small differences in its coordination geometry (Figure 2). Whereas 3 a contains a square-planar coordination site, the absence of the hydride ligand in 4 a results in a minor distortion towards a Y-shaped arrangement of the N donor atoms around the Ni center. The central NiNcentral bond is slightly shortened on going from 3 a to 4 a (average values: 1.9349(18) to 1.920(2) ), whereas the NiNox distances become slightly longer (1.8604(18) to Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
Figure 2. a) Molecular structure of deuterido complex 3 a[D]. Only one of the two independent molecules is shown, hydrogen atoms are removed for clarity. Selected bond length [] and angles [8]: Ni1–N3 1.8632(19)/[1.8544(17)], Ni1–N1 1.8649(19)/[1.8589(17)], Ni1–N2 1.9368(18)/[1.9311(17)], N3-Ni1-N1 172.65(9)/[172.53(8)], N2-Ni1-D1 174.6(10)/[176.5(11)], N3-Ni1-N2 93.45(8)/[93.34(8)], N1-Ni1-N2 93,80(8)/[94,10(8)]; b) molecular structure of 4 a. Selected bond length [] and angles [8]: Ni–N1 1.875(2), Ni–N3 1.877(2), Ni–N2 1.920(2), N1-Ni-N3 169.44(9), N1-Ni-N2 94,52(9), N3-Ni-N2 96,00’(10); c) SOMO-orbital of 4 a calculated at the open shell DFT B3LYP/6-311G(d,p) level (isovalue of 0.4).
1.876(2) ) and the NcentralNiN angles widen (93.67(8) to 95.26(10) 8). Nevertheless, the coordination geometry of 4 a remains very close to the ideal T-shaped geometry in compari-
9658
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper son to other nickel(I) structures described in literature Table 1. Catalyst screening for selected substrates. as such.[6b, 8] In view of the observed importance of the ligand rearrangement, which gives rise to the conjugated pelectron system, for the formation of the NiI species Entry Substrate t Cat. Yield ee (no such transformation was observed for 1 a–d), the [%][a] [%] question inevitably arose as to the degree in which the unpaired electron in 4 is located on the ligand 48 h 4a 81 49 1 itself. In other words, we were interested to assess whether the complex was better described as 2 48 h 4b 50 51 a ligand-located rather than as a metal-centered radical, a notion which has implications for the assign3 48 h 4c 28 13 ment of the redox state at the metal. The spin density distribution calculated using open 4 48 h 4d 81 33 shell DFT methods at the B3LYP/6-311G(d,p)[9, 10] level clearly indicates a mainly metal-located unpaired 5 5d 4a 59 74 electron with a Mulliken atomic spin density of 0.97 at the nickel atom. The g value (gav = 2.16) of the EPR resonances of 4 a–d (see the Supporting Information) 6 5d 4d 48 46 observed by X-band EPR spectroscopy has been adequately modeled by the DFT study which supports [a] Conversion determined by 1H NMR spectroscopy after work-up using an internal standard. the assignment of complexes 4 a–d as nickel(I) com[1d] pounds. These new chiral nickel(I) complexes were found to catalyze the asymmetric hydrodehalogenation of Table 2. Substrate scope of the asymmetric hydrodehalogenation. geminal dihalogenides with moderate-to-good enantiomeric excesses (ee values, Table 1 and Table 2). The reactions were carried out in THF as solvent using LiEt3BH as reductant. Among the catalysts tested the nickel complex 4 a, containing the phenyl-substituted Entry Substrate t T Yield ee ligand, yielded the best results (Table 1). The main [8C] [%][a] [%] side product generally observed is the dehalogenat48 h 20 81 49 1 ed alkene, whereas the hydrodehalogenation of the chiral monohalogen compound occurred much more 2 48 h 20 84 47 slowly despite the large excess of reductant. Dibromoalkanes reacted faster than dichloro compounds, however, LiEt3BH itself is capable of reducing the di48 h 20 83 42 3 bromoalkanes below room temperature, whereas in the case of dichloroalkanes no significant non-cata5d 20 59 74 4 lyzed background reaction is observed at temperatures of up to 60 8C. 5 3d 0 84 70 As indicated above, hydrodehalogenations can be carried out using a wide range of different homoge3d 0 36 21 6 neous or heterogeneous catalysts, but it previously proved very difficult to obtain significant chiral induc48 h 50 63 48 7 tion in such a transformation. Given the promising results obtained with the nickel complexes reported in 8 3d 78 74 60 this work, we aimed to gain a better understanding of the processes involved in this reaction. To this end, [a] Conversion determined by 1H NMR spectroscopy after work-up using an internal a series of mechanistic studies was carried out to esstandard. tablish the active species in the process and to address the question at which stage the stereochemistry of the products was determined. lene with 4 a as catalyst displayed a linear correlation for the Initially we probed the possibility of the involvement of sevgiven temperature range, indicating a single mechanism for eral competing reaction pathways: An Eyring plot of the enanthe catalysis (Figure 3).[11] Furthermore, the enantiomeric excess tiomeric ratio of the product obtained from the catalytic hydrodehalogenation of 2,2-dichloro-1,2,3,4-tetrahydronaphthawas found to be constant during the course of the reaction Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
9659
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper
Figure 3. Eyring plot of the enantiomeric ratio (e.r.) of the product obtained from the catalytic hydrodehalogenation of 2,2-dichloro-1,2,3,4-tetrahydronaphthalene with 4 a as catalyst.
(see the Supporting Information), and the presence of mercury had no effect on the outcome. Thus, the participation of a heterogeneous colloidal system as (a potentially competing)[1b, 12] reactive species in the catalysis appears unlikely. In addition, the formation of nickel(0) colloids through disproportionation of the nickel(I) complex as described in the literature for other nickel(I) species[13] was not observed when 4 a was heated in toluene at 110 8C for several hours. As a precatalyst the halogenido (e.g., 2) or acetato nickel(II) complexes could also be used. In the catalytic reaction, these compounds were transformed very rapidly to the corresponding hydrido species 3, which then slowly dehydrogenated to give the NiI complex 4 (k = 5.31 104 mol1 L s1, see above). This conversion to 4 initially limits the activity of the catalyst system until a steady state concentration of 4 is attained. The importance of nickel(I) for the catalytic reaction was demonstrated using the radical scavenger 2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO) during the ongoing catalytic conversion. After the addition at 20 8C of a quantity of 7.5 mol % of TEMPO, which corresponded to half the catalyst loading (15 mol %) in the given experiment, the generation of the product immediately halted. After 3 h (in the case at hand, the time required for the complete reduction of TEMPO) the transformation re-started and the reaction continued to full conversion (Figure 4). The fact that the concentration of starting material during the inhibition remained constant indicated that the reaction did not stop due to the trapping of possibly generated organic radical intermediates, but that the initial step of the catalytic cycle is suppressed. Stoichiometric reactions involving the individual species represented in the TEMPO inhibition cycle depicted in Figure 4 were carried out: The NiH complexes 3 a did not directly react with TEMPO under the chosen conditions, whereas the corresponding nickel(I) species very rapidly formed the NiII-TEMPO addition product 5 a, which subsequently reacted with LiEt3BH to give the nickel hydrido complex 3 a again. During the inhibition of the catalytic cycle the concentration of 3 a remained nearly constant, whereas TEMPO acted as a nickel(I) scavenger and thereby inhibited the initial reaction with the dichloro substrate. Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
Figure 4. Top: Effect of the addition of TEMPO (7.5 mol %) during the catalysis on the course of the reaction monitored by 1H NMR spectroscopy. Bottom: Processes causing the halt of the catalytic reaction (left) and molecular structure of the isolated complex 5 a (right).
The key role of nickel(I) in the initiation step of the catalytic dehalogenation led us to investigate its behavior in stoichiometric reactions with organohalides, which act as radical probes. Rearrangements were observed both in the stoichiometric conversion with (bromomethyl)cyclopropane as well as supermesityl bromide (Scheme 3 a and b), as expected for the occurrence of radical intermediates.[14] A similar behavior was observed in the catalytic reduction of supermesityl bromide using LiEt3BD (Scheme 3 c). To clarify the nature of the hydride transferring species during the catalysis, a competition experiment was carried out with the deuterido nickel complex 3 a[D] and LiEt3BH. A clear preference for the incorporation of deuterium at the early stage of the experiment was observed (Scheme 3 d), indicating that the nickel hydrido complex is the hydrogen atom transfer reagent to the organic substrate rather than LiEt3BH (see the Supporting Information). Furthermore, the fact that the product of the catalysis is obtained enantiomerically enriched and that the transformation can be run stoichiometrically with the same ee value by using only the in situ-generated nickel hydrido complex and the substrate also indicates that the hydrido complex is indeed transferring the hydride onto the substrate during the catalysis.
9660
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper period of the catalysis when nickel(I) is added as precatalyst. Nickel(I) reacts with the substrate to give the radical intermediate, which is then trapped by another nickel(I) complex instead of being reduced by the nickel hydrido species as in the main catalytic cycle. This is the two-site oxidative addition as represented in the stoichiometric reactions in Scheme 3 a and b. The nickel chloride complex, which is formed, is transformed by LiEt3BH to the nickel hydrido complex and re-enters the catalytic cycle. We propose that the a-chloroalkyl complex eliminates the dechlorinated alkene as observed experimentally and the resulting NiCl species is transformed rapidly to the hydride as discussed above. These transformations proceed until the concentration of nickel(I) has decreased to a level at which the competitive reduction of the intermediate radical by the hydrido complex is favored. The second regulatory path is the dynamic equilibrium between 3 and 4 mentioned above, through which the nickel(I) species is continuously reformed. To further support this mechanistic proposal depicted in Scheme 4 and to substantiate the key role of NiH as the enantioselective hydrogen transfer reagent in the catalytic cycle, the reaction with 2,2-dichloro-1,2,3,4-tetrahydronaphthalene (entry 1, Table 2) was run at 20 8C using tris(trimethylsilyl)silane (TTMSS) as hydride source and nickel(I) as precatalyst (Scheme 5). TTMSS is incapable of transferring the hydride
Scheme 3. a), b) Stoichiometric reactions of 4 a with bromo compounds; c) isomerization of the bromo-2,4,6-tri-tert-butylbenzene-derived radical during the catalytic hydrodehalogenation; d) competition experiment for the hydride transfer onto the substrate of the catalysis between LigNiD and LiEt3BH.
Scheme 5. Reaction scheme for the catalytic hydrodehalogenation using tris(trimethylsilyl)silane (TTMSS) and 4 a as radical initiator.
Scheme 4. Proposed mechanism for the catalytic cycle of the hydrodehalogenation of geminal dihalogenes.
The proposed mechanism for the catalytic conversion under steady state conditions based on the observations described above is depicted in Scheme 4. The main catalytic cycle contains the initial reaction of nickel(I) 4 with the dihalogeno substrate 8 to form the halogenido complex 2 and the organoradical 9 (possibly in rapid equilibrium with a metal-stabilized form 10), which is enantioselectively reduced by the hydrido nickel complex 3 to yield the product of the catalytic reaction 11 and simultaneously regenerates the nickel(I) complex 4. Crucial for the observed catalytic activity is the nickel(I) concentration, which is mainly regulated through two different pathways that dominate depending on whether the NiI complex is employed as catalyst or the nickel(II) hydrido complex is generated initially from an appropriate NiII precursor. The downregulation in c(NiI) occurs predominantly at the initial Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
either to the nickel(I) or to the nickelchlorido complex. Control experiments also excluded the possibility of a direct reaction of TTMSS with the dichloro substrate under the chosen conditions of the catalysis. In the catalytic transformation depicted in Scheme 5 the racemic mixture of the corresponding monochloro-substituted reaction product was obtained. TTMSS is known to hydrodehalogenate organohalides at elevated temperatures in the presence of radical starters.[15] This is consistent with a nickel(I)-initiated radical halide abstraction step and a subsequent silane-based hydrogen atom transfer that mimics the role of the chiral nickel hydride in the catalytic reaction. The silane being achiral, the resulting product has to be racemic, as was observed.
9661
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper Conclusion
Preparation of (R)-LigPh(iso)NiCl (2 a)
We have developed a chiral nickel-based hydrodehalogenation catalyst that acts as a molecular system capable of mono-dehalogenating prochiral geminal organodihalogenides with significant enantioselectivities. A detailed mechanistic study has unraveled the key species involved in the dehalogenation and the subsequent enantioselective hydrogen-transfer step. The well-behaved molecular nature of the system, along with the mechanistic insight obtained in this study will provide the basis for the further development of this methodology.
Experimental Section All manipulations of air- and moisture-sensitive materials were performed under an inert atmosphere of dry argon using standard Schlenk techniques or by working in a glovebox. Solvents were dried over sodium (toluene), potassium (hexanes) or sodium/potassium alloy (pentane, diethyl ether), distilled, and degassed prior to use.[16] Deuterated solvents were dried over potassium (C6D6, [D8]toluene, [D8]THF), vacuum distilled and stored in Teflon valve ampoules under argon. Samples for NMR spectroscopy were prepared under argon in 5 mm Wilmad tubes equipped with J. Young Teflon valves. 1H- and 13C NMR spectra were recorded on Bruker Avance 200, 400 and 600 NMR spectrometers and were referenced internally using the residual protio solvent (1H) or solvent (13C).[17] Elemental analyses were recorded by the analytical service of the Heidelberg Chemistry Department. The enantioselectivities of the products obtained from the catalytic hydrodehalogenation were measured on a Finnigan Focus GC device using a Chiraldex G-TA column. The phenyl-, isopropyl-, tert-butyl- and indandiyl-substituted bis(oxazolinylmethyl)pyrrole protioligands (LigphH, LigiPrH, LigtBuH, LigindH) and complexes 1 b, 2 b and the corresponding acetato complex (LigiPr(iso)NiOAc) were synthesized according to literature.[5b,c] All other reagents were obtained from commercial sources and used as received unless explicitly stated otherwise. For Compounds 1–4, and the geminal dihalides the experimental detail of only one representative example is shown here. Details of the preparative procedures and characterization data for all other compounds reported in this work as well as the atom labeling are given in the Supporting Information.
Preparation of (R)-LigPhNiCl (1 a) NaH (3.39 mmol, 1.4 equiv) was added at 0 8C to a solution of the protioligand (LigphH; 936 mg, 2.43 mmol) in THF (20 mL), and stirred for 1 h. The solution was subsequently filtered and canulated to a suspension of [NiCl2(dme)] (dme = dimethoxyethane) (4.86 mmol, 2 equiv) and THF (20 mL) at low temperature. After the mixture was stirred for another 2 h at 0 8C the solvents were removed. The residue was treated with a toluene/pentane (3:1) mixture and the inorganic metal salts were filtered off. After the removal of the solvents, the product was recrystallized from a dichloromethane/pentane mixture to give the product as dark-red crystalline solid in 72 % yield (840 mg). 1H NMR ([D8]toluene, 399.890 MHz, 190 K): d = 7.40–6.77 (m, 10 H, H8, 9, 10), 6.07 (s, 2 H, H1), 5.29 (m, 2 H, H6), 3.56–2.86 ppm (m, 8 H, H3, 3’, 5, 5’);13C NMR ([D8]toluene, 100.552 MHz, 190 K): d = 170.5 (C4), 141.8 (C7), 130.0– 123.6 (C8/9/10), 124.7 (C2), 106.4 (C1), 75.8 (C5), 65.4 (C6), 27.5 ppm (C3); HRMS (DART +): m/z calcd for C24H2335ClN358NiO2 : 478.0832; found: 478.0838; elemental analysis calcd (%) for C24H22ClN3NiO2 : C 60.23, H 4.63, N 8.78; found: C 60.23, H 4.72, N 8.85. Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
Complex 1 a (705 mg, 1.47 mmol) was dissolved in toluene (40 mL) and heated to 90 8C for 8 h. The solvent was removed and the product was recrystallized from a dichloromethane/pentane mixture to give the product as dark-brown crystalline solid in 93 % yield (655 mg). 1H NMR (C6D6, 600.130 MHz, 295 K): d = 7.35 (m, 4 H, H8), 7.19 (m, 4 H, H9), 7.06 (m, 2 H, H10), 5.71 (dd, 3J = 8.8 Hz, 3J = 2.9 Hz 2 H, H6), 4.79 (s, 2 H, H3), 3.57 (dd, 2J = 8.3 Hz, 3J = 8.7 Hz, 2 H, H5), 3.54 (dd, 2J = 8.2 Hz, 3J = 3.0 Hz, 2 H, H5’), 1.92–1.77 ppm (m, 4 H, H1, 1’); 13C NMR (C6D6, 150.903 MHz, 295 K): d = 170.7 (C2), 163.7 (C4), 144.7 (C7), 128.8 (C9), 127.5 (C10), 126.9 (C8), 82.2 (C3), 74.0 (C5), 66.5 (C6), 30.5 ppm (C1); HRMS (DART +): m/z calcd: for C24H2335ClN358NiO2 : 478.0832; found: 478.0843; elemental analysis calcd (%) for C24H22ClN3NiO2 : C 60.23, H 4.63, N 8.78; found: C 59.90, H 4.63, N 8.72.
Preparation of (R)-LigPh(iso)NiOAc To a suspension of nickel(II) acetate tetrahydrate (0.82 g, 3.28 mmol, 1.2 equiv) in methanol (15 mL), a solution of the protioligand (LigphH; 1.06 g, 2.74 mmol) in methanol (15 mL) was added. After stirring for 18 h at room temperature, the solvent was removed under reduced pressure, toluene was added and the solution was filtered. After removal of the solvents, the product was recrystallized from a dichloromethane/pentane mixture to give the product as red crystalline solid in 80 % yield (1.09 g, 2.17 mmol).1H NMR (CDCl3, 399.890 MHz, 233 K): d = 7.44–7.36 (m, 4 H, H9), 7.36–7.29 (m, 2 H, H10), 7.25–7.16 (m, 4 H, H8), 5.20 (m, 2 H, H6), 4.65 (s, 2 H, H3), 4.31 (dd, 2J = 8.3 Hz, 3J = 8.3 Hz, 2 H, H5), 4.15 (d, 3J = 8.1 Hz, 2 H, H5’), 2.50 (m, 4 H, H1, 1’), 1.73 ppm (s, 3 H, H12);13C NMR (CDCl3, 100.552 MHz, 233 K): d = 173.5 (C2), 168.0 (C11), 166.8 (C4), 144.2 (C7), 128.9 (C9), 127.7 (C10), 125.7 (C8), 83.4 (C3), 77.7 (C5), 69.3 (C6), 38.2 (C1), 29.2 ppm (C12); HRMS (FAB +): m/z calcd for C26H25N3NiO4 : 501.1199; found: 501.1198; elemental analysis calcd (%) for C26H25N3NiO4 : C 62.18, H 5.02, N 8.37; found: C 61.99, H 4.93, N 8.38.
Preparation of (R)-LigPhNiI (4 a) LiEt3BH (2.84 mmol, 1.2 equiv, 1 m in THF) was added to a solution of the nickel(II) acetato complex ((R)-LigPh(iso)NiOAc; 1.19 g, 2.36 mmol) in toluene (20 mL), at 78 8C. After 10 min, the cooling bath was removed and the reaction was stirred for another 40 min. Pentane (80 mL) was added and the solution was filtrated, concentrated to 3 mL and stirred for 2 h at 90 8C under reduced pressure. Subsequently, the solvent was removed completely and the product was recrystallized from a toluene/pentane mixture at 40 8C to give a dark-red crystalline solid in 82 % yield (860 mg). Magnetic susceptibility (Evans method): meff = 1.92 mB; ESR (X-Band, toluene, 9.444404 GHz, 120 K) gx = 2.326, gy = 2.147, gz = 2.038, Az = 14.6 G; 1 H NMR ([D8]toluene, 600.130 MHz, 295 K): d = 27.1 (H6), 13.2 (H8), 8.0 (H10), 6.4 (H5), 5.7 (H5’), 4.8 (H9), 8.2 (H3), 39.2 ppm (H1, 1’); IR (KBr): n˜ = 2962 (w), 2894 (w), 1952 (w), 1878 (w), 1811 (w), 1606 (s), 1589 (s), 1535 (s), 1338 (m), 1288 (m), 1250 (s), 1215 (s), 1000 (s), 960 (m), 768 (m), 733 (m), 698 cm1 (s); HRMS (FAB +); m/z calcd for C24H22N358NiO2 : 442.1066; found: 442.1079; elemental analysis calcd (%) for C24H22N3NiO2 : C 65.05, H 5.00, N 9.48; found: C 64.82, H 5.18, N 9.20.
Preparation of (R)-LigPhNiH[D] (3 a/3 a[D]) A solution of the nickel(I) complex 4 a (18.4 mg, 0.042 mmol) in a toluene/pentane mixture was subjected to a 10 bar H2 (D2) pres-
9662
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper sure. After 48 h, crystals had formed and the solution was decanted and finally completely removed under reduced pressure to give the product in 75 % yield (14 mg). 1H NMR ([D8]toluene, 600.130 MHz, 295 K): d = 7.17–7.08 (m, 8 H, H8, 9), 7.08–7.02 (m, 2 H, H10), 5.12 (s, 2 H, H3), 4.46 (m, 2 H, H6), 3.74 (m, 2 H, H5), 3.65 (m, 2 H, H5’), 2.29 (m, 4 H, H1, 1’), 24.86 ppm (s, 1 H, H11); 13C NMR ([D8]toluene, 150.903 MHz, 295 K): d = 169.5 (C2), 165.0 (C4), 145.7 (C7), 128.6 (C9), 127.3 (C8), 127.2 (C10), 80.7 (C3), 75.6 (C6), 73.6 (C5), 30.9 ppm (C1); IR (KBr): n˜ = 3025 (w), 2953 (w), 2891 (w), 1858 (NiH) (s), 1593 (s), 1522 (s), 1451 (m), 1432 (m), 1340 (m), 1289 (s), 1249 (s), 1215 (s), 1069 (m), 1018 (s), 979 (s), 733 (s), 699 (s), 533 cm1 (m); HRMS (FAB +): m/z calcd for C24H22DN360NiO2 : 446.1161; found: 446.1117; m/z calcd for C24H22DN358NiO2 (444.1207) and C24H22N360NiO2 (444.1020): one signal at m/z 444.1074 was found; elemental analysis calcd (%) for C24H23N3NiO2 : C 64.90, H 5.22, N 9.46; found: C 64.85, H 5.32, N 9.13.
Preparation of (R)-LigPhNi-TEMPO (5 a) A solution of TEMPO (14.1 mg, 0.090 mmol, 1 equiv) in a toluene/ pentane (1:3) mixture (1 mL) was added to a solution of complex 4 a (40 mg, 0.090) in toluene (0.5 mL), at room temperature and stirred for 5 min. Subsequently, pentane (3 mL) was added and the reaction mixture was stored at 40 8C to give the product as darkbrown crystalline solid in 67 % yield (36 mg). 1H NMR ([D8]toluene, 399.890 MHz, 238 K): d = 7.70 (d, 3J = 7.5 Hz, 2 H, H8), 7.26–6.96 (m, 9 H, H6, 9, 10, 18, 19, 20), 5.13 (d, 3J = 7.4 Hz, 1 H, H16), 5.06 (s, 1 H, H3/13), 4.94 (s, 1 H, H3/13), 4.14 (dt, 2J = 8.1 Hz, 3J = 8.1 Hz, 1 H, H5), 3.98 (d, J = 8.0 Hz, 1 H, H5’), 3.80 (dt, J = 7.7 Hz, J = 7.6 Hz, 1 H, H15), 3.67 (d, J = 7.8 Hz, 1 H, H15‘), 2.08 (s, 3 H, H26), 2.00–1.71 (m, 4 H, H1, 1‘, 11, 11’), 1.59–1.09 (m, 6 H, H22, 22’, 23, 23’, 24, 24’), 1.14 (s, 3 H, H28), 0.91 (s, 3 H, H29), 0.28 ppm (s, 3 H, H27); 13C NMR ([D8]toluene, 100.552 MHz, 238 K): d = 171.4 (C2/12), 171.2 (C2/12), 165.2 (C14), 164.1 (C4), 145.7 (C7), 144.9 (C17), 128.9 (C9), 128.1 (C19), 126.7 (C10/20), 126.3 (C10/20), 126.3 (C8), 125.4 (C18), 82.2 (C3/13), 81.2 (C3/13), 75.7 (C5), 74.8 (C15), 59.1 (C16), 58.1 (C25), 58.1 (C21), 55.3 (C6), 41.1 (C24), 40.8 (C22), 34.7 (C26), 31.2 (C28), 30.5 (C1/11), 30.3 (C1/11), 23.5 (C29), 20.2 (C27), 18.1 ppm (C23); HRMS (DART +): m/z calcd for C33H40N458NiO3 : 599.2532; found: 599.2532; elemental analysis calcd (%) for C33H40N4NiO3 : C 66.13, H 6.73, N 9.35; found: C 65.65, H 6.74, N 9.17.
Preparation of (R)-LigPhNi-butenyl (6 a) After the activation of Mg turnings (80 mg) by traces I2, (bromomethyl)cyclopropane (78 mg, 0.57 mmol) dissolved in THF (5 mL) was added and stirred for 2 h at RT. The reaction mixture was filtered and canulated to a solution of the nickel chlorido complex 2 a (97 mg, 0.20 mmol) at 0 8C. After 10 min, the solvents were removed and the residue was treated with a toluene/pentane mixture (1:20), stirred for 15 min and filtrated. After removal of the solvents, the product was obtained as yellow powder in 75 % yield (75 mg). The direct reaction of the nickel(I) complex 4 a with an excess of (bromomethyl)cyclopropane in C6D6 at room temperature led to the same isomerized compound (6 a). 1H NMR (C6D6, 600.130 MHz, 295 K): d = 7.21 (d, 3J = 7.5 Hz, 4 H, H8), 7.12 (m, 4 H, H9), 7.01 (m, 2 H, H10), 5.79 (m, 1 H, H13), 5.16 (s, 2 H, H3), 4.91 (dd, 3 J = 8.6 Hz, 3J = 2.1 Hz, 2 H, H6), 4.90–4.84 (m, 2 H, H14, 14‘), 3.74 (dd, 2 J = 8.1 Hz, 3J = 8.6 Hz, 2 H, H5), 3.64 (dd, 2J = 8.1 Hz, 3J = 2.5 Hz, 2 H, H5‘), 2.24–2.10 (m, 5 H, H1, 1‘, 12), 2.04 (m, 1 H, H12‘), 0.75 (m, 1 H, H11), 0.54 ppm (m, 1 H, H11‘); 13C NMR (C6D6, 150.903 MHz, 295 K): d = 171.5 (C2), 165.9 (C4), 144.9 (C7), 141.1 (C13), 128.9 (C9), 127.5 (C10), 126.1 (C8), 110.6 (C14), 81.0 (C3), 73.5 (C5), 67.8 (C6), 37.0 (C12), 31.1 (C1), 10.3 ppm (C11); HRMS (FAB +): m/z calcd for C24H22N358NiO2 : 497.1613; found: 497.1667. Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
Preparation of (R)-LigPhNi-(iso)supermesityl (7 a) A solution of 1-bromo-2,4,6-tri(tert-butyl)benzene (47 mg, 0.144 mg, 1 equiv) in THF (5 mL) was added to a solution of the nickel(I) complex 4 a (127 mg, 0.287 mmol) in THF (2 mL), and was stirred for 2 h. The solvents were removed and the residue was treated with pentane, stirred for 30 min and filtered. After removal of the solvents, the product was obtained as an orange solid in 45 % yield (90 mg). 1H NMR (C6D6, 600.130 MHz, 295 K): d = 7.61 (d, 4 J = 1.6 Hz, 2 H, H16), 7.34–7.21 (m, 4 H, H8), 7.32 (m, 1 H, H18), 7.14 (m, 4 H, H9), 7.02 (t, 3J = 7.4 Hz, 2 H, H10), 5.10 (s, 2 H, H3), 4.73 (dd, 3 J = 8.5 Hz, 3J = 2.2 Hz, 2 H, H6), 3.48 (dd, 2J = 7.6 Hz, 3J = 2.3 Hz, 2 H, H5), 3.35–3.15 (m, 2 H, H5‘), 2.71 (s, 3 H, H13), 2.27 (m, 4 H, H1, 1‘), 1.40 (s, 18 H, H20), 1.18 (d, 2J = 9.2 Hz, 1 H, H11), 1.07 (d, 2J = 9.2 Hz, 1 H, H11’), 0.77 ppm (s, 3 H, H14); 13C NMR (C6D6, 150.903 MHz, 295 K): d = 170.8 (C2), 165.0 (C4), 153.5 (C15), 149.4 (C17), 145.1 (C7), 129.0 (C9), 127.6 (C10), 126.4 (C8), 121.4 (C16), 118.8 (C18), 80.5 (C3), 73.5 (C5), 69.8 (C6), 42.8 (C12), 35.1 (C13), 34.2 (C19), 31.9 (C20), 30.9 (C1), 29.1 (C14), 20.2 ppm (C11); HRMS (DART +): m/z calcd for C42H52N358NiO2 : 688.3413; found: 688.3428; elemental analysis calcd (%) for C42H41N3NiO2 : C 73.26, H 7.47, N 6.10; found: C 72.74, H 7.95, N 5.42.
Preparation of geminal dihalides The geminal dihalides used as substrates for the catalysis were prepared following the methodology by Takeda et al.[18] 2,2-Dichloro-1,2,3,4-tetrahydronaphthalene: Yield: 810 mg colorless solid, 47 %.1H NMR (CDCl3, 600.130 MHz, 295 K): d = 7.22–7.12 (m, 3 H, H7, 6, 5), 7.04 (s, 1 H, H8), 3.69 (s, 2 H, H1), 3.10 (t, 3J = 6.6 Hz, 2 H, H4), 2.62 ppm (t, 3J = 6.6 Hz, 2 H, H3); 13C NMR (CDCl3, 150.903 MHz, 295 K): d = 133.1 (C10), 132.5 (C9), 128.9 (C5), 128.7 (C8), 127.1 (C6/7), 126.5 (C6/7), 88.2 (C2), 50.1 (C1), 42.5 (C3), 28.3 ppm (C4); HR-MS (EI +): m/z calcd for C10H1035L2 : 200.0160; found: 200.0151; elemental analysis calcd (%) for C10H10Cl2 : C 59.73, H 5.01; found: C 59.86, H 5.05.
General procedure for the catalytic conversion of geminal dichlorides using LiEt3BH as reductant A solution of the catalyst (7.5 mol % in 0.2 mL THF) was slowly added to a solution of the geminal dichloride (0.099 mmol) and LiEt3BH (0.20 mol) in THF (0.5 mL) at the indicated temperature. After the given time, the reaction was quenched using a saturated NH4Cl solution and the reaction products were extracted with pentane (3 1 mL). After removal of the volatiles, the crude was dissolved in a pentane/diethyl ether (9:1) mixture and flushed through a silica plug (washed with 3 1 mL of the 9:1 mixture). After removal of the solvents, the product was dissolved in CDCl3 and 1,4-dimethoxybenzene as internal standard was added to determine the yield of the reaction. GC analysis was performed to determine the enantiomeric excess of the product.
General procedure for the catalytic conversion of geminal dibromides using LiEt3BH as reductant LiEt3BH (0.6 mL of 1.0 m THF solution, 0.60 mol) was added to a solution of the catalyst (9.9 mg, 7.5 mol %) in THF (1.2 mL), and cooled to the indicated temperature. A solution of the dibromide (0.29 mmol in 0.6 mL) was added slowly and stirred for the given time. The reaction mixture was treated using the work-up procedure and analytic methods described above.
9663
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper Determination of the enantiomeric excess by chiral GC analysis Fused Silica Capillary GC Column: Astec Chiraldex G-TA (2,6-di-Opentyl-3-trifluoroacetyl derivative of g-cyclodextrin); Dimension: 50 m 0.25 mm; Film thickness: 0.12 mm; Carrier gas: He. For a detailed description of the methodologies used see the Supporting Information.
ods;[23] 4 a: direct methods with dual-space recycling;[24] 5 a: charge flip.[25] Refinement: full-matrix least squares methods based on F2 ; all non-hydrogen atoms anisotropic, hydrogen atoms (except the deuterides in 3 a, which were refined) at calculated positions (refined riding).[26] CCDC-978128 (3 a), CCDC-978129 (4 a), CCDC-978130 (5 a) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Computational studies (general) The unrestricted DFT-B3LYP computational tool[9] has been employed to model complex 4 a with a 6-311g(d,p) basis set.[10] All the calculations have been carried out with the Gaussian 09 program package.[19] Stationary points were verified by frequency analysis. The Cartesian coordinates of the optimized structure of 4 a are available in the Supporting Information.
Acknowledgements We thank Prof. Dr. M. Enders, Dr. Marion Kerscher, Jan Freudenberg, Mathias Ronellenfitsch and Tim Stçßer for advice and experimental support. We acknowledge funding by the Deutsche Forschungsgemeinschaft (SFB 623, TP B6).
Calculation of EPR parameters The g-values of complex 4 a were calculated using the Orca software (version 2.9.1).[20] Therefore, the optimized geometry above was used as input geometry and the eprnmr feature on the B3LYP/ 6-311G*(d,p) level was applied. Scalar relativistic corrections were applied for the electron structure calculations, and SO interactions were accounted for using the mean-field approx. Spin-orbit mean field (SOMF; incl. both spin-own-orbit and spin-other-orbit interactions).[21] G values (calcd): gx = 2.042, gy = 2.183, gz = 2.216.
Keywords: asymmetric catalysis enantioselectivity · nickel · radicals
Crystal data Complex 3 a: C24H22DN3NiO2, M = 445.17, monoclinic, space group P21, a = 14.39570(10), b = 7.40300(10), c = 19.3928(2) , b = 104.6980(8) 8, V = 1999.09(4) 3, Z = 4, dcalcd = 1.4790 Mg m3, CuKa radiation, l = 1.5418 , m = 1.613 mm1, F000 = 928. T = 115(1) K, q range 3.4 to 72.0 8. Index ranges h, k, l: 17…17, 8…7, 23…23. Reflections measured: 60 179; independent: 7185 [Rint = 0.027]; observed [I > 2s(I)]: 7162. Final R indices [Fo > 4s(Fo)]: R(F) = 0.0220, wR(F2) = 0.0605, GooF = 1.039, residual dens. = 0.36, 0.20 e 3, abs. structure parm. 0.001(8). Complex 4 a: C24H22N3NiO2, M = 443.15, orthorhombic, space group P212 121, a = 8.714(4), b = 10.859(6), c = 20.875(11) , V= 1975.3(18) 3, Z = 4, dcalcd = 1.490 Mg·m3, MoKa radiation, l = 0.71073 , m = 1.009 mm1, F000 = 924. T = 100(1) K, q range 2.0 to 32.2 8. Index ranges h, k, l: 12…12, 16…16, 30…31. Reflections measured: 41198, independent: 6672 [Rint = 0.051], observed. [I > 2s(I)]: 5820. Final R indices [Fo > 4s(Fo)]: R(F) = 0.0327, wR(F2) = 0.0650, GooF = 0.949, residual dens. = 0.47, 0.30 e 3, abs. structure parm. 0.009(5). Complex 5 a·0.5 n-pentane: C35.5H46N4NiO3, M = 635.47, orthorhombic, space group P212121, a = 14.0328(6), b = 15.5952(6), c = 29.2027(15) , V = 6390.8(5) 3, Z = 8, dcalcd = 1.321 Mg·m3, CuKa radiation, l = 1.5418 , m = 1.200 mm1, F000 = 2712. T = 110(1) K, q range 4.0 to 67.9 8. Index ranges h, k, l: 16…16, 18…18, 34…30. Reflections measured: 168 170; independent: 11 472 [Rint = 0.208]; observed [I > 2s(I)]: 8019. Final R indices [Fo > 4s(Fo)]: R(F) = 0.0631, wR(F2) = 0.1481, GooF = 0.966, residual dens. = 0.47, 0.76 e 3, abs. structure parm. 0.03(2). Data collection: Agilent Technologies Supernova-E CCD diffractometer, microfocus X-Ray tube, multilayer mirror optics (complexes 3 a and 5 a) or Bruker AXS Smart 1000 CCD diffractometer, graphite monochromator (complex 4 a). Lorentz, polarization and numerical (3 a, 5 a)/semiempirical absorption correction.[22] Structure solution: 3 a: heavy atom method combined with structure expansion by direct methChem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
9664
·
dehalogenation
·
[1] Selected key references for mechanistic investigations on CC coupling and hydrodehalogenation reactions: a) A. Bakac, J. H. Espenson, J. Am. Chem. Soc. 1986, 108, 719 – 723; b) F. Alonso, I. P. Beletskaya, M. Yus, Chem. Rev. 2002, 102, 4009 – 4092; c) T. J. Anderson, G. D. Jones, D. A. Vicic, J. Am. Chem. Soc. 2004, 126, 8100 – 8101; d) G. D. Jones, J. L. Martin, C. McFarland, O. R. Allen, R. E. Hall, A. D. Haley, R. J. Brandon, T. Konovalova, P. J. Desrochers, P. Pulay, D. A. Vicic, J. Am. Chem. Soc. 2006, 128, 13175 – 13183; e) V. B. Phapale, E. BuÇuel, M. Garca-Iglesias, D. J. Crdenas, Angew. Chem. 2007, 119, 8946 – 8951; Angew. Chem. Int. Ed. 2007, 46, 8790 – 8795; f) X. Hu, Chem. Sci. 2011, 2, 1867 – 1886; g) J. Breitenfeld, J. Ruiz, M. D. Wodrich, X. Hu, J. Am. Chem. Soc. 2013, 135, 12004 – 12012. [2] Selected references for Ni-catalyzed enantioselective CC coupling reactions: a) F. O. Arp, G. C. Fu, J. Am. Chem. Soc. 2005, 127, 10482 – 10483; b) F. Glorius, Angew. Chem. 2008, 120, 8474 – 8476; Angew. Chem. Int. Ed. 2008, 47, 8347 – 8349; c) A. Rudolph, M. Lautens, Angew. Chem. 2009, 121, 2694 – 2708; Angew. Chem. Int. Ed. 2009, 48, 2656 – 2670; d) J. Choi, G. C. Fu, J. Am. Chem. Soc. 2012, 134, 9102 – 9105; e) J. T. Binder, C. J. Cordier, G. C. Fu, J. Am. Chem. Soc. 2012, 134, 17003 – 17006. [3] a) R. Hazard, S. Jaouannet, A. Tallec, Tetrahedron 1982, 38, 93 – 102; b) H.-U. Blaser, S. K. Boyer, U. Pittelkow, Tetrahedron: Asymmetry 1991, 2, 721 – 732; c) M. F. Kuehnel, T. Schlçder, S. Riedel, B. Nieto-Ortega, F. J. Ramrez, J. T. Lpez Navarrete, J. Casado, D. Lentz, Angew. Chem. 2012, 124, 2261 – 2263; Angew. Chem. Int. Ed. 2012, 51, 2218 – 2220. [4] a) D. G. Kelley, A. Marchaj, A. Bakac, J. H. Espenson, J. Am. Chem. Soc. 1991, 113, 7583 – 7587; b) B. B. Wayland, G. Poszmik, S. L. Mukerjee, M. Fryd, J. Am. Chem. Soc. 1994, 116, 7943 – 7944. [5] a) C. Mazet, L. H. Gade, Chem. Eur. J. 2003, 9, 1759 – 1767; b) F. Konrad, J. Lloret Fillol, C. Rettenmeier, H. Wadepohl, L. H. Gade, Eur. J. Inorg. Chem. 2009, 4950 – 4961; c) F. Konrad, J. Lloret Fillol, H. Wadepohl, L. H. Gade, Inorg. Chem. 2009, 48, 8523 – 8535. [6] Selected key references for NiI complexes based on N-containing ligands: a) P. L. Holland, T. R. Cundari, L. L. Perez, N. A. Eckert, R. J. Lachicotte, J. Am. Chem. Soc. 2002, 124, 14416 – 14424; b) E. Kogut, A. Zeller, T. H. Warren, T. Strassner, J. Am. Chem. Soc. 2004, 126, 11984 – 11994; c) S. Pfirrmann, C. Limberg, C. Herwig, R. Stçßer, B. Ziemer, Angew. Chem. 2009, 121, 3407 – 3411; Angew. Chem. Int. Ed. 2009, 48, 3357 – 3361; d) S. Wiese, P. Kapoor, K. D. Williams, T. H. Warren, J. Am. Chem. Soc. 2009, 131, 18105 – 18111; e) S. Yao, Y. Xiong, C. Milsmann, E. Bill, S. Pfirrmann, C. Limberg, M. Driess, Chem. Eur. J. 2010, 16, 436 – 439; f) S. Yao, M. Driess, Acc. Chem. Res. 2012, 45, 276 – 287; g) S. Wiese, J. L. McAfee, D. R. Pahls, C. L. McMullin, T. R. Cundari, T. H. Warren, J. Am. Chem. Soc. 2012, 134, 10114 – 10121; h) C. Uyeda, J. C. Peters, Chem. Sci. 2013, 4, 157 – 163; i) B. Horn, C. Limberg, C. Herwig, B. Braun, Chem. Commun. 2013, 49, 10923 – 10925; j) H. Gehring, R. Metzinger, C. 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper
[7]
[8]
[9]
[10]
[11]
[12]
[13] [14]
Herwig, J. Intemann, S. Harder, C. Limberg, Chem. Eur. J. 2013, 19, 1629 – 1636. Selected key references for NiI complexes based on P-containing ligands: a) D. A. Vicic, W. D. Jones, J. Am. Chem. Soc. 1999, 121, 7606 – 7617; b) D. J. Mindiola, G. L. Hillhouse, J. Am. Chem. Soc. 2001, 123, 4623 – 4624; c) R. Melenkivitz, D. J. Mindiola, G. L. Hillhouse, J. Am. Chem. Soc. 2002, 124, 3846 – 3847; d) D. A. Vicic, T. J. Anderson, J. A. Cowan, A. J. Schultz, J. Am. Chem. Soc. 2004, 126, 8132 – 8133; e) Y. Chen, C. Sui-Seng, D. Zargarian, Angew. Chem. 2005, 117, 7899 – 7903; Angew. Chem. Int. Ed. 2005, 44, 7721 – 7725; f) A. L. Keen, M. Doster, S. A. Johnson, J. Am. Chem. Soc. 2007, 129, 810 – 819; g) V. M. Iluc, G. L. Hillhouse, J. Am. Chem. Soc. 2010, 132, 11890 – 11892. a) C. Eaborn, M. S. Hill, P. B. Hitchcock, J. D. Smith, Chem. Commun. 2000, 691 – 692; b) K. D. Kitiachvili, D. J. Mindiola, G. L. Hillhouse, J. Am. Chem. Soc. 2004, 126, 10554 – 10555; c) E. Kogut, H. L. Wiencko, L. Zhang, D. E. Cordeau, T. H. Warren, J. Am. Chem. Soc. 2005, 127, 11248 – 11249; d) N. A. Eckert, A. Dinescu, T. R. Cundari, P. L. Holland, Inorg. Chem. 2005, 44, 7702 – 7704. a) A. D. Becke, Phys. Rev. A 1988, 38, 3098 – 3100; b) B. Miehlich, A. Savin, H. Stoll, H. Preuss, Chem. Phys. Lett. 1989, 157, 200 – 206; c) A. D. Becke, J. Chem. Phys. 1993, 98, 5648 – 5652. a) A. J. H. Wachters, J. Chem. Phys. 1970, 52, 1033 – 1036; b) P. J. Hay, J. Chem. Phys. 1977, 66, 4377 – 4384; c) R. Krishnan, J. S. Binkley, R. Seeger, J. A. Pople, J. Chem. Phys. 1980, 72, 650 – 654; d) A. D. McLean, G. S. Chandler, J. Chem. Phys. 1980, 72, 5639 – 5648; e) C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785 – 789; f) K. Raghavachari, G. W. Trucks, J. Chem. Phys. 1989, 91, 1062 – 1065; g) R. C. Binning, L. A. Curtiss, J. Comput. Chem. 1990, 11, 1206 – 1216; h) M. P. McGrath, L. Radom, J. Chem. Phys. 1991, 94, 511 – 516; i) L. A. Curtiss, M. P. McGrath, J. P. Blaudeau, N. E. Davis, R. C. Binning, L. Radom, J. Chem. Phys. 1995, 103, 6104 – 6113; j) J.-P. Blaudeau, M. P. McGrath, L. A. Curtiss, L. Radom, J. Chem. Phys. 1997, 107, 5016 – 5021. a) H. Buschmann, H.-D. Scharf, N. Hoffmann, P. Esser, Angew. Chem. 1991, 103, 480 – 518; Angew. Chem. Int. Ed. Engl. 1991, 30, 477 – 515; b) T. Gçbel, K. B. Sharpless, Angew. Chem. 1993, 105, 1417 – 1418; Angew. Chem. Int. Ed. Engl. 1993, 32, 1329 – 1331. Nickel(II) chloride itself was found to act as a precatalyst for the hydrodehalogenation, most likely due to the formation of reactive nickel(0) particles under the reaction conditions (therefore see: A. Roy, V. Srinivas, S. Ram, J. A. De Toro, J. P. Goff, J. Appl. Phys. 2006, 100, 094307). J. Breitenfeld, R. Scopelliti, X. Hu, Organometallics 2012, 31, 2128 – 2136. a) G. Brunton, D. Griller, L. R. C. Barclay, K. U. Ingold, J. Am. Chem. Soc. 1976, 98, 6803 – 6811; b) D. Griller, K. U. Ingold, Acc. Chem. Res. 1980, 13, 317 – 323; c) B. C. Childress, A. C. Rice, P. B. Shevlin, J. Org. Chem. 1974, 39, 3056 – 3058; d) D. C. Nonhebel, Chem. Soc. Rev. 1993, 22, 347 – 359; e) D. Zhu, I. Korobkov, P. H. M. Budzelaar, Organometallics 2012, 31, 3958 – 3971.
Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
[15] a) T. Fukuyama, M. Kobayashi, M. T. Rahman, N. Kamata, I. Ryu, Org. Lett. 2008, 10, 533 – 536; b) J. Wang, Z. Zhu, W. Huang, M. Deng, X. Zhou, J. Organomet. Chem. 2008, 693, 2188 – 2192. [16] W. L. F. Armarego, C. L. L. Chai, Purification of Laboratory Chemicals, Elsevier/Butterworth-Heinemann, 2009. [17] G. R. Fulmer, A. J. M. Miller, N. H. Sherden, H. E. Gottlieb, A. Nudelman, B. M. Stoltz, J. E. Bercaw, K. I. Goldberg, Organometallics 2010, 29, 2176 – 2179. [18] T. Takeda, R. Sasaki, S. Yamauchi, T. Fujiwara, Tetrahedron 1997, 53, 557. [19] Gaussian 09, Revision A.02, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, J. E. Peralta., Jr., F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, . Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian, Inc., Wallingford CT, 2009. [20] F. Neese, ORCA: An ab initio, Density Functional and Semiempirical Program Package, Version 2.9.1 (MPI f r Chemische Energiekonversion). [21] F. Neese, J. Chem. Phys. 2001, 115, 11080. [22] a) SAINT, Bruker AXS, Karlsruhe, 1997 – 2011; b) R. H. Blessing, Acta Crystallogr. Sect. A 1995, 51, 33; c) G. M. Sheldrick, SADABS, Bruker AXS, Karlsruhe, 2004 – 2008; d) CrysAlisPro, Agilent Technologies UK Ltd., Oxford 2011;e) SCALE3 ABSPACK, CrysAlisPro, Agilent Technologies UK Ltd., Oxford 2011. [23] a) P. T. Beurskens, G. Beurskens, R. de Gelder, J. M. M. Smits, S. GarciaGranda, R. O. Gould, DIRDIF-2008, Radboud University Nijmegen, The Netherlands, 2008; b) P. T. Beurskens, in Crystallographic Computing 3 (Eds.: G. M. Sheldrick, C. Kr ger, R. Goddard), Clarendon, Oxford, 1985, p. 216. [24] a) G. M. Sheldrick, SHELXD, University of Gçttingen and Bruker Nonius 2000 – 4; b) G. M. Sheldrick, H. A. Hauptman, C. M. Weeks, R. Miller, I. Usn in International Tables for Crystallography, Vol. F (Eds.: M. G. Rossmann, E. Arnold), IUCr/Kluwer, Dordrecht 2001, pp. 333 – 351. [25] a) L. Palatinus, SUPERFLIP, EPF Lausanne, Switzerland 2007; b) L. Palatinus, G. Chapuis, J. Appl. Crystallogr. 2007, 40, 786. [26] a) G. M. Sheldrick, SHELXL-2012, University of Gçttingen, 2013; b) G. M. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112.
Received: April 25, 2014
9665
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper
& Asymmetric Catalysis
Stereoselective Hydrodehalogenation via a Radical-Based Mechanism Involving T-Shaped Chiral Nickel(I) Pincer Complexes Christoph Rettenmeier, Hubert Wadepohl, and Lutz H. Gade*[a] Dedicated to Professor Helmut Werner on the occasion of his 80th birthday
Abstract: We herein report the catalytic enantioselective hydrodehalogenation based on the interplay of a chiral molecular nickel(I)/nickel(II)hydride system. Prochiral geminal dihalogenides are dehalogenated via a secondary configurationally unstable, potentially metal-stabilized radical intermediate. In a subsequent step, the liberated radical is then trapped by the nickel(II) hydrido complex, present in a large excess under the catalytic conditions, which in turn induces the enantioselectivity during the hydrogen atom transfer
onto the radical intermediate. These new chiral nickel(I) complexes were found to catalyze the asymmetric hydrodehalogenation of geminal dihalogenides with moderate to good enantiomeric excess values using LiEt3BH as reductant. The main side product generally observed is the dehalogenated alkene, whereas the hydrodehalogenation of the chiral monohalogen compound occurred much more slowly despite the large excess of reductant.
Introduction Radical-based mechanistic pathways have been proposed both for nickel-catalyzed hydrodehalogenations and related CC coupling reactions.[1] For the latter, remarkable enantioselectivities have been achieved using chiral molecular catalysts.[2] On the other hand, whereas there have been a few attempts to achieve enantioselective hydrodehalogenation,[3] no example we are aware of employs a well-defined chiral molecular catalyst. A key question underlying the development of enantioselective hydrodehalogenation involving potential radical intermediates and multiple oxidation states of the metal concern the mechanism of stereo induction in such a transformation. Our approach is based on the partial hydrodehalogenation of prochiral geminal dihalides catalyzed by a molecular Ni catalyst. Two distinct molecular forms in different oxidation states interact with the substrate as well as the resulting reaction intermediate in subsequent steps of the catalytic transformation. Both nickel complexes contain the same chiral ligand, however, their role during the catalysis differs substantially: In a first step, the nickel(I) complex abstracts a halogen atom from the geminal dihalogenide, generating a nickel(II) chlorido complex and a configurationally labile radical species. The latter may be stabilized by a reversible coordination to the generated NiCl complex.[4] In a subsequent step, the liberated radical is then trapped by the nickel(II) hydrido complex, present in a large [a] C. Rettenmeier, Prof. Dr. H. Wadepohl, Prof. Dr. L. H. Gade Anorganisch-Chemisches Institut, Univeristt Heidelberg Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) E-mail: [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201403243. Chem. Eur. J. 2014, 20, 9657 – 9665
Scheme 1. Reactivity pattern observed for the hydrodehalogenation.
excess under the catalytic conditions, which in turn induces the enantioselectivity during the hydrogen atom transfer onto the radical intermediate (Scheme 1).
Results and Discussion We have previously reported the synthesis of the bisoxazolinmethylpyrrolido nickel chlorido complex 1 b and investigated its isomerization to the bis(oxazolinylmethylidene)pyrrolidinido complex 2 b (Scheme 2).[5] The rearrangement involves the planarization of the pincer ligand in which a conjugated 10-pelectron system strongly interacts with the metal center resulting in a significant stabilization. The latter has been found to be essential for the synthesis of a series of remarkably stable nickel(I) complexes[6, 7] by the reaction of the chlorido nickel complexes with LiEt3BH. The nickel hydrido complexes 3, which are initially formed, undergo H2 elimination to generate the T-shaped nickel(I) species 4 (Figure 1). K¼
9657
cðLigNiHÞ2 cðLigNiI Þ2 pðH2 Þ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper
Scheme 2. Synthesis of new nickel hydrido complexes 3 and nickel(I) complexes 4.
Figure 1. Second-order dependency on the concentration of 3 a for the rate of hydrogen elimination in 3 a at 273 K.
In solution the nickel(I) and nickel hydrido complexes are in a hydrogen pressure-dependent dynamic equilibrium (K = 12.4 bar1 at 295 K for 3 a/4 a, Scheme 2) with the rate of the NiIIH!NiI interconversion being of second order in hydrido complex concentration, which is consistent with a bimolecular mechanism (k = 5.31 104 L mol1 s1 at 273 K for 4 a; Figure 1). Single-crystal X-ray structure analyses of 3 a and 4 a established an almost perfectly planar ligand frame in a meridional coordination to the nickel center with small differences in its coordination geometry (Figure 2). Whereas 3 a contains a square-planar coordination site, the absence of the hydride ligand in 4 a results in a minor distortion towards a Y-shaped arrangement of the N donor atoms around the Ni center. The central NiNcentral bond is slightly shortened on going from 3 a to 4 a (average values: 1.9349(18) to 1.920(2) ), whereas the NiNox distances become slightly longer (1.8604(18) to Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
Figure 2. a) Molecular structure of deuterido complex 3 a[D]. Only one of the two independent molecules is shown, hydrogen atoms are removed for clarity. Selected bond length [] and angles [8]: Ni1–N3 1.8632(19)/[1.8544(17)], Ni1–N1 1.8649(19)/[1.8589(17)], Ni1–N2 1.9368(18)/[1.9311(17)], N3-Ni1-N1 172.65(9)/[172.53(8)], N2-Ni1-D1 174.6(10)/[176.5(11)], N3-Ni1-N2 93.45(8)/[93.34(8)], N1-Ni1-N2 93,80(8)/[94,10(8)]; b) molecular structure of 4 a. Selected bond length [] and angles [8]: Ni–N1 1.875(2), Ni–N3 1.877(2), Ni–N2 1.920(2), N1-Ni-N3 169.44(9), N1-Ni-N2 94,52(9), N3-Ni-N2 96,00’(10); c) SOMO-orbital of 4 a calculated at the open shell DFT B3LYP/6-311G(d,p) level (isovalue of 0.4).
1.876(2) ) and the NcentralNiN angles widen (93.67(8) to 95.26(10) 8). Nevertheless, the coordination geometry of 4 a remains very close to the ideal T-shaped geometry in compari-
9658
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper son to other nickel(I) structures described in literature Table 1. Catalyst screening for selected substrates. as such.[6b, 8] In view of the observed importance of the ligand rearrangement, which gives rise to the conjugated pelectron system, for the formation of the NiI species Entry Substrate t Cat. Yield ee (no such transformation was observed for 1 a–d), the [%][a] [%] question inevitably arose as to the degree in which the unpaired electron in 4 is located on the ligand 48 h 4a 81 49 1 itself. In other words, we were interested to assess whether the complex was better described as 2 48 h 4b 50 51 a ligand-located rather than as a metal-centered radical, a notion which has implications for the assign3 48 h 4c 28 13 ment of the redox state at the metal. The spin density distribution calculated using open 4 48 h 4d 81 33 shell DFT methods at the B3LYP/6-311G(d,p)[9, 10] level clearly indicates a mainly metal-located unpaired 5 5d 4a 59 74 electron with a Mulliken atomic spin density of 0.97 at the nickel atom. The g value (gav = 2.16) of the EPR resonances of 4 a–d (see the Supporting Information) 6 5d 4d 48 46 observed by X-band EPR spectroscopy has been adequately modeled by the DFT study which supports [a] Conversion determined by 1H NMR spectroscopy after work-up using an internal standard. the assignment of complexes 4 a–d as nickel(I) com[1d] pounds. These new chiral nickel(I) complexes were found to catalyze the asymmetric hydrodehalogenation of Table 2. Substrate scope of the asymmetric hydrodehalogenation. geminal dihalogenides with moderate-to-good enantiomeric excesses (ee values, Table 1 and Table 2). The reactions were carried out in THF as solvent using LiEt3BH as reductant. Among the catalysts tested the nickel complex 4 a, containing the phenyl-substituted Entry Substrate t T Yield ee ligand, yielded the best results (Table 1). The main [8C] [%][a] [%] side product generally observed is the dehalogenat48 h 20 81 49 1 ed alkene, whereas the hydrodehalogenation of the chiral monohalogen compound occurred much more 2 48 h 20 84 47 slowly despite the large excess of reductant. Dibromoalkanes reacted faster than dichloro compounds, however, LiEt3BH itself is capable of reducing the di48 h 20 83 42 3 bromoalkanes below room temperature, whereas in the case of dichloroalkanes no significant non-cata5d 20 59 74 4 lyzed background reaction is observed at temperatures of up to 60 8C. 5 3d 0 84 70 As indicated above, hydrodehalogenations can be carried out using a wide range of different homoge3d 0 36 21 6 neous or heterogeneous catalysts, but it previously proved very difficult to obtain significant chiral induc48 h 50 63 48 7 tion in such a transformation. Given the promising results obtained with the nickel complexes reported in 8 3d 78 74 60 this work, we aimed to gain a better understanding of the processes involved in this reaction. To this end, [a] Conversion determined by 1H NMR spectroscopy after work-up using an internal a series of mechanistic studies was carried out to esstandard. tablish the active species in the process and to address the question at which stage the stereochemistry of the products was determined. lene with 4 a as catalyst displayed a linear correlation for the Initially we probed the possibility of the involvement of sevgiven temperature range, indicating a single mechanism for eral competing reaction pathways: An Eyring plot of the enanthe catalysis (Figure 3).[11] Furthermore, the enantiomeric excess tiomeric ratio of the product obtained from the catalytic hydrodehalogenation of 2,2-dichloro-1,2,3,4-tetrahydronaphthawas found to be constant during the course of the reaction Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
9659
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper
Figure 3. Eyring plot of the enantiomeric ratio (e.r.) of the product obtained from the catalytic hydrodehalogenation of 2,2-dichloro-1,2,3,4-tetrahydronaphthalene with 4 a as catalyst.
(see the Supporting Information), and the presence of mercury had no effect on the outcome. Thus, the participation of a heterogeneous colloidal system as (a potentially competing)[1b, 12] reactive species in the catalysis appears unlikely. In addition, the formation of nickel(0) colloids through disproportionation of the nickel(I) complex as described in the literature for other nickel(I) species[13] was not observed when 4 a was heated in toluene at 110 8C for several hours. As a precatalyst the halogenido (e.g., 2) or acetato nickel(II) complexes could also be used. In the catalytic reaction, these compounds were transformed very rapidly to the corresponding hydrido species 3, which then slowly dehydrogenated to give the NiI complex 4 (k = 5.31 104 mol1 L s1, see above). This conversion to 4 initially limits the activity of the catalyst system until a steady state concentration of 4 is attained. The importance of nickel(I) for the catalytic reaction was demonstrated using the radical scavenger 2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO) during the ongoing catalytic conversion. After the addition at 20 8C of a quantity of 7.5 mol % of TEMPO, which corresponded to half the catalyst loading (15 mol %) in the given experiment, the generation of the product immediately halted. After 3 h (in the case at hand, the time required for the complete reduction of TEMPO) the transformation re-started and the reaction continued to full conversion (Figure 4). The fact that the concentration of starting material during the inhibition remained constant indicated that the reaction did not stop due to the trapping of possibly generated organic radical intermediates, but that the initial step of the catalytic cycle is suppressed. Stoichiometric reactions involving the individual species represented in the TEMPO inhibition cycle depicted in Figure 4 were carried out: The NiH complexes 3 a did not directly react with TEMPO under the chosen conditions, whereas the corresponding nickel(I) species very rapidly formed the NiII-TEMPO addition product 5 a, which subsequently reacted with LiEt3BH to give the nickel hydrido complex 3 a again. During the inhibition of the catalytic cycle the concentration of 3 a remained nearly constant, whereas TEMPO acted as a nickel(I) scavenger and thereby inhibited the initial reaction with the dichloro substrate. Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
Figure 4. Top: Effect of the addition of TEMPO (7.5 mol %) during the catalysis on the course of the reaction monitored by 1H NMR spectroscopy. Bottom: Processes causing the halt of the catalytic reaction (left) and molecular structure of the isolated complex 5 a (right).
The key role of nickel(I) in the initiation step of the catalytic dehalogenation led us to investigate its behavior in stoichiometric reactions with organohalides, which act as radical probes. Rearrangements were observed both in the stoichiometric conversion with (bromomethyl)cyclopropane as well as supermesityl bromide (Scheme 3 a and b), as expected for the occurrence of radical intermediates.[14] A similar behavior was observed in the catalytic reduction of supermesityl bromide using LiEt3BD (Scheme 3 c). To clarify the nature of the hydride transferring species during the catalysis, a competition experiment was carried out with the deuterido nickel complex 3 a[D] and LiEt3BH. A clear preference for the incorporation of deuterium at the early stage of the experiment was observed (Scheme 3 d), indicating that the nickel hydrido complex is the hydrogen atom transfer reagent to the organic substrate rather than LiEt3BH (see the Supporting Information). Furthermore, the fact that the product of the catalysis is obtained enantiomerically enriched and that the transformation can be run stoichiometrically with the same ee value by using only the in situ-generated nickel hydrido complex and the substrate also indicates that the hydrido complex is indeed transferring the hydride onto the substrate during the catalysis.
9660
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper period of the catalysis when nickel(I) is added as precatalyst. Nickel(I) reacts with the substrate to give the radical intermediate, which is then trapped by another nickel(I) complex instead of being reduced by the nickel hydrido species as in the main catalytic cycle. This is the two-site oxidative addition as represented in the stoichiometric reactions in Scheme 3 a and b. The nickel chloride complex, which is formed, is transformed by LiEt3BH to the nickel hydrido complex and re-enters the catalytic cycle. We propose that the a-chloroalkyl complex eliminates the dechlorinated alkene as observed experimentally and the resulting NiCl species is transformed rapidly to the hydride as discussed above. These transformations proceed until the concentration of nickel(I) has decreased to a level at which the competitive reduction of the intermediate radical by the hydrido complex is favored. The second regulatory path is the dynamic equilibrium between 3 and 4 mentioned above, through which the nickel(I) species is continuously reformed. To further support this mechanistic proposal depicted in Scheme 4 and to substantiate the key role of NiH as the enantioselective hydrogen transfer reagent in the catalytic cycle, the reaction with 2,2-dichloro-1,2,3,4-tetrahydronaphthalene (entry 1, Table 2) was run at 20 8C using tris(trimethylsilyl)silane (TTMSS) as hydride source and nickel(I) as precatalyst (Scheme 5). TTMSS is incapable of transferring the hydride
Scheme 3. a), b) Stoichiometric reactions of 4 a with bromo compounds; c) isomerization of the bromo-2,4,6-tri-tert-butylbenzene-derived radical during the catalytic hydrodehalogenation; d) competition experiment for the hydride transfer onto the substrate of the catalysis between LigNiD and LiEt3BH.
Scheme 5. Reaction scheme for the catalytic hydrodehalogenation using tris(trimethylsilyl)silane (TTMSS) and 4 a as radical initiator.
Scheme 4. Proposed mechanism for the catalytic cycle of the hydrodehalogenation of geminal dihalogenes.
The proposed mechanism for the catalytic conversion under steady state conditions based on the observations described above is depicted in Scheme 4. The main catalytic cycle contains the initial reaction of nickel(I) 4 with the dihalogeno substrate 8 to form the halogenido complex 2 and the organoradical 9 (possibly in rapid equilibrium with a metal-stabilized form 10), which is enantioselectively reduced by the hydrido nickel complex 3 to yield the product of the catalytic reaction 11 and simultaneously regenerates the nickel(I) complex 4. Crucial for the observed catalytic activity is the nickel(I) concentration, which is mainly regulated through two different pathways that dominate depending on whether the NiI complex is employed as catalyst or the nickel(II) hydrido complex is generated initially from an appropriate NiII precursor. The downregulation in c(NiI) occurs predominantly at the initial Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
either to the nickel(I) or to the nickelchlorido complex. Control experiments also excluded the possibility of a direct reaction of TTMSS with the dichloro substrate under the chosen conditions of the catalysis. In the catalytic transformation depicted in Scheme 5 the racemic mixture of the corresponding monochloro-substituted reaction product was obtained. TTMSS is known to hydrodehalogenate organohalides at elevated temperatures in the presence of radical starters.[15] This is consistent with a nickel(I)-initiated radical halide abstraction step and a subsequent silane-based hydrogen atom transfer that mimics the role of the chiral nickel hydride in the catalytic reaction. The silane being achiral, the resulting product has to be racemic, as was observed.
9661
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper Conclusion
Preparation of (R)-LigPh(iso)NiCl (2 a)
We have developed a chiral nickel-based hydrodehalogenation catalyst that acts as a molecular system capable of mono-dehalogenating prochiral geminal organodihalogenides with significant enantioselectivities. A detailed mechanistic study has unraveled the key species involved in the dehalogenation and the subsequent enantioselective hydrogen-transfer step. The well-behaved molecular nature of the system, along with the mechanistic insight obtained in this study will provide the basis for the further development of this methodology.
Experimental Section All manipulations of air- and moisture-sensitive materials were performed under an inert atmosphere of dry argon using standard Schlenk techniques or by working in a glovebox. Solvents were dried over sodium (toluene), potassium (hexanes) or sodium/potassium alloy (pentane, diethyl ether), distilled, and degassed prior to use.[16] Deuterated solvents were dried over potassium (C6D6, [D8]toluene, [D8]THF), vacuum distilled and stored in Teflon valve ampoules under argon. Samples for NMR spectroscopy were prepared under argon in 5 mm Wilmad tubes equipped with J. Young Teflon valves. 1H- and 13C NMR spectra were recorded on Bruker Avance 200, 400 and 600 NMR spectrometers and were referenced internally using the residual protio solvent (1H) or solvent (13C).[17] Elemental analyses were recorded by the analytical service of the Heidelberg Chemistry Department. The enantioselectivities of the products obtained from the catalytic hydrodehalogenation were measured on a Finnigan Focus GC device using a Chiraldex G-TA column. The phenyl-, isopropyl-, tert-butyl- and indandiyl-substituted bis(oxazolinylmethyl)pyrrole protioligands (LigphH, LigiPrH, LigtBuH, LigindH) and complexes 1 b, 2 b and the corresponding acetato complex (LigiPr(iso)NiOAc) were synthesized according to literature.[5b,c] All other reagents were obtained from commercial sources and used as received unless explicitly stated otherwise. For Compounds 1–4, and the geminal dihalides the experimental detail of only one representative example is shown here. Details of the preparative procedures and characterization data for all other compounds reported in this work as well as the atom labeling are given in the Supporting Information.
Preparation of (R)-LigPhNiCl (1 a) NaH (3.39 mmol, 1.4 equiv) was added at 0 8C to a solution of the protioligand (LigphH; 936 mg, 2.43 mmol) in THF (20 mL), and stirred for 1 h. The solution was subsequently filtered and canulated to a suspension of [NiCl2(dme)] (dme = dimethoxyethane) (4.86 mmol, 2 equiv) and THF (20 mL) at low temperature. After the mixture was stirred for another 2 h at 0 8C the solvents were removed. The residue was treated with a toluene/pentane (3:1) mixture and the inorganic metal salts were filtered off. After the removal of the solvents, the product was recrystallized from a dichloromethane/pentane mixture to give the product as dark-red crystalline solid in 72 % yield (840 mg). 1H NMR ([D8]toluene, 399.890 MHz, 190 K): d = 7.40–6.77 (m, 10 H, H8, 9, 10), 6.07 (s, 2 H, H1), 5.29 (m, 2 H, H6), 3.56–2.86 ppm (m, 8 H, H3, 3’, 5, 5’);13C NMR ([D8]toluene, 100.552 MHz, 190 K): d = 170.5 (C4), 141.8 (C7), 130.0– 123.6 (C8/9/10), 124.7 (C2), 106.4 (C1), 75.8 (C5), 65.4 (C6), 27.5 ppm (C3); HRMS (DART +): m/z calcd for C24H2335ClN358NiO2 : 478.0832; found: 478.0838; elemental analysis calcd (%) for C24H22ClN3NiO2 : C 60.23, H 4.63, N 8.78; found: C 60.23, H 4.72, N 8.85. Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
Complex 1 a (705 mg, 1.47 mmol) was dissolved in toluene (40 mL) and heated to 90 8C for 8 h. The solvent was removed and the product was recrystallized from a dichloromethane/pentane mixture to give the product as dark-brown crystalline solid in 93 % yield (655 mg). 1H NMR (C6D6, 600.130 MHz, 295 K): d = 7.35 (m, 4 H, H8), 7.19 (m, 4 H, H9), 7.06 (m, 2 H, H10), 5.71 (dd, 3J = 8.8 Hz, 3J = 2.9 Hz 2 H, H6), 4.79 (s, 2 H, H3), 3.57 (dd, 2J = 8.3 Hz, 3J = 8.7 Hz, 2 H, H5), 3.54 (dd, 2J = 8.2 Hz, 3J = 3.0 Hz, 2 H, H5’), 1.92–1.77 ppm (m, 4 H, H1, 1’); 13C NMR (C6D6, 150.903 MHz, 295 K): d = 170.7 (C2), 163.7 (C4), 144.7 (C7), 128.8 (C9), 127.5 (C10), 126.9 (C8), 82.2 (C3), 74.0 (C5), 66.5 (C6), 30.5 ppm (C1); HRMS (DART +): m/z calcd: for C24H2335ClN358NiO2 : 478.0832; found: 478.0843; elemental analysis calcd (%) for C24H22ClN3NiO2 : C 60.23, H 4.63, N 8.78; found: C 59.90, H 4.63, N 8.72.
Preparation of (R)-LigPh(iso)NiOAc To a suspension of nickel(II) acetate tetrahydrate (0.82 g, 3.28 mmol, 1.2 equiv) in methanol (15 mL), a solution of the protioligand (LigphH; 1.06 g, 2.74 mmol) in methanol (15 mL) was added. After stirring for 18 h at room temperature, the solvent was removed under reduced pressure, toluene was added and the solution was filtered. After removal of the solvents, the product was recrystallized from a dichloromethane/pentane mixture to give the product as red crystalline solid in 80 % yield (1.09 g, 2.17 mmol).1H NMR (CDCl3, 399.890 MHz, 233 K): d = 7.44–7.36 (m, 4 H, H9), 7.36–7.29 (m, 2 H, H10), 7.25–7.16 (m, 4 H, H8), 5.20 (m, 2 H, H6), 4.65 (s, 2 H, H3), 4.31 (dd, 2J = 8.3 Hz, 3J = 8.3 Hz, 2 H, H5), 4.15 (d, 3J = 8.1 Hz, 2 H, H5’), 2.50 (m, 4 H, H1, 1’), 1.73 ppm (s, 3 H, H12);13C NMR (CDCl3, 100.552 MHz, 233 K): d = 173.5 (C2), 168.0 (C11), 166.8 (C4), 144.2 (C7), 128.9 (C9), 127.7 (C10), 125.7 (C8), 83.4 (C3), 77.7 (C5), 69.3 (C6), 38.2 (C1), 29.2 ppm (C12); HRMS (FAB +): m/z calcd for C26H25N3NiO4 : 501.1199; found: 501.1198; elemental analysis calcd (%) for C26H25N3NiO4 : C 62.18, H 5.02, N 8.37; found: C 61.99, H 4.93, N 8.38.
Preparation of (R)-LigPhNiI (4 a) LiEt3BH (2.84 mmol, 1.2 equiv, 1 m in THF) was added to a solution of the nickel(II) acetato complex ((R)-LigPh(iso)NiOAc; 1.19 g, 2.36 mmol) in toluene (20 mL), at 78 8C. After 10 min, the cooling bath was removed and the reaction was stirred for another 40 min. Pentane (80 mL) was added and the solution was filtrated, concentrated to 3 mL and stirred for 2 h at 90 8C under reduced pressure. Subsequently, the solvent was removed completely and the product was recrystallized from a toluene/pentane mixture at 40 8C to give a dark-red crystalline solid in 82 % yield (860 mg). Magnetic susceptibility (Evans method): meff = 1.92 mB; ESR (X-Band, toluene, 9.444404 GHz, 120 K) gx = 2.326, gy = 2.147, gz = 2.038, Az = 14.6 G; 1 H NMR ([D8]toluene, 600.130 MHz, 295 K): d = 27.1 (H6), 13.2 (H8), 8.0 (H10), 6.4 (H5), 5.7 (H5’), 4.8 (H9), 8.2 (H3), 39.2 ppm (H1, 1’); IR (KBr): n˜ = 2962 (w), 2894 (w), 1952 (w), 1878 (w), 1811 (w), 1606 (s), 1589 (s), 1535 (s), 1338 (m), 1288 (m), 1250 (s), 1215 (s), 1000 (s), 960 (m), 768 (m), 733 (m), 698 cm1 (s); HRMS (FAB +); m/z calcd for C24H22N358NiO2 : 442.1066; found: 442.1079; elemental analysis calcd (%) for C24H22N3NiO2 : C 65.05, H 5.00, N 9.48; found: C 64.82, H 5.18, N 9.20.
Preparation of (R)-LigPhNiH[D] (3 a/3 a[D]) A solution of the nickel(I) complex 4 a (18.4 mg, 0.042 mmol) in a toluene/pentane mixture was subjected to a 10 bar H2 (D2) pres-
9662
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper sure. After 48 h, crystals had formed and the solution was decanted and finally completely removed under reduced pressure to give the product in 75 % yield (14 mg). 1H NMR ([D8]toluene, 600.130 MHz, 295 K): d = 7.17–7.08 (m, 8 H, H8, 9), 7.08–7.02 (m, 2 H, H10), 5.12 (s, 2 H, H3), 4.46 (m, 2 H, H6), 3.74 (m, 2 H, H5), 3.65 (m, 2 H, H5’), 2.29 (m, 4 H, H1, 1’), 24.86 ppm (s, 1 H, H11); 13C NMR ([D8]toluene, 150.903 MHz, 295 K): d = 169.5 (C2), 165.0 (C4), 145.7 (C7), 128.6 (C9), 127.3 (C8), 127.2 (C10), 80.7 (C3), 75.6 (C6), 73.6 (C5), 30.9 ppm (C1); IR (KBr): n˜ = 3025 (w), 2953 (w), 2891 (w), 1858 (NiH) (s), 1593 (s), 1522 (s), 1451 (m), 1432 (m), 1340 (m), 1289 (s), 1249 (s), 1215 (s), 1069 (m), 1018 (s), 979 (s), 733 (s), 699 (s), 533 cm1 (m); HRMS (FAB +): m/z calcd for C24H22DN360NiO2 : 446.1161; found: 446.1117; m/z calcd for C24H22DN358NiO2 (444.1207) and C24H22N360NiO2 (444.1020): one signal at m/z 444.1074 was found; elemental analysis calcd (%) for C24H23N3NiO2 : C 64.90, H 5.22, N 9.46; found: C 64.85, H 5.32, N 9.13.
Preparation of (R)-LigPhNi-TEMPO (5 a) A solution of TEMPO (14.1 mg, 0.090 mmol, 1 equiv) in a toluene/ pentane (1:3) mixture (1 mL) was added to a solution of complex 4 a (40 mg, 0.090) in toluene (0.5 mL), at room temperature and stirred for 5 min. Subsequently, pentane (3 mL) was added and the reaction mixture was stored at 40 8C to give the product as darkbrown crystalline solid in 67 % yield (36 mg). 1H NMR ([D8]toluene, 399.890 MHz, 238 K): d = 7.70 (d, 3J = 7.5 Hz, 2 H, H8), 7.26–6.96 (m, 9 H, H6, 9, 10, 18, 19, 20), 5.13 (d, 3J = 7.4 Hz, 1 H, H16), 5.06 (s, 1 H, H3/13), 4.94 (s, 1 H, H3/13), 4.14 (dt, 2J = 8.1 Hz, 3J = 8.1 Hz, 1 H, H5), 3.98 (d, J = 8.0 Hz, 1 H, H5’), 3.80 (dt, J = 7.7 Hz, J = 7.6 Hz, 1 H, H15), 3.67 (d, J = 7.8 Hz, 1 H, H15‘), 2.08 (s, 3 H, H26), 2.00–1.71 (m, 4 H, H1, 1‘, 11, 11’), 1.59–1.09 (m, 6 H, H22, 22’, 23, 23’, 24, 24’), 1.14 (s, 3 H, H28), 0.91 (s, 3 H, H29), 0.28 ppm (s, 3 H, H27); 13C NMR ([D8]toluene, 100.552 MHz, 238 K): d = 171.4 (C2/12), 171.2 (C2/12), 165.2 (C14), 164.1 (C4), 145.7 (C7), 144.9 (C17), 128.9 (C9), 128.1 (C19), 126.7 (C10/20), 126.3 (C10/20), 126.3 (C8), 125.4 (C18), 82.2 (C3/13), 81.2 (C3/13), 75.7 (C5), 74.8 (C15), 59.1 (C16), 58.1 (C25), 58.1 (C21), 55.3 (C6), 41.1 (C24), 40.8 (C22), 34.7 (C26), 31.2 (C28), 30.5 (C1/11), 30.3 (C1/11), 23.5 (C29), 20.2 (C27), 18.1 ppm (C23); HRMS (DART +): m/z calcd for C33H40N458NiO3 : 599.2532; found: 599.2532; elemental analysis calcd (%) for C33H40N4NiO3 : C 66.13, H 6.73, N 9.35; found: C 65.65, H 6.74, N 9.17.
Preparation of (R)-LigPhNi-butenyl (6 a) After the activation of Mg turnings (80 mg) by traces I2, (bromomethyl)cyclopropane (78 mg, 0.57 mmol) dissolved in THF (5 mL) was added and stirred for 2 h at RT. The reaction mixture was filtered and canulated to a solution of the nickel chlorido complex 2 a (97 mg, 0.20 mmol) at 0 8C. After 10 min, the solvents were removed and the residue was treated with a toluene/pentane mixture (1:20), stirred for 15 min and filtrated. After removal of the solvents, the product was obtained as yellow powder in 75 % yield (75 mg). The direct reaction of the nickel(I) complex 4 a with an excess of (bromomethyl)cyclopropane in C6D6 at room temperature led to the same isomerized compound (6 a). 1H NMR (C6D6, 600.130 MHz, 295 K): d = 7.21 (d, 3J = 7.5 Hz, 4 H, H8), 7.12 (m, 4 H, H9), 7.01 (m, 2 H, H10), 5.79 (m, 1 H, H13), 5.16 (s, 2 H, H3), 4.91 (dd, 3 J = 8.6 Hz, 3J = 2.1 Hz, 2 H, H6), 4.90–4.84 (m, 2 H, H14, 14‘), 3.74 (dd, 2 J = 8.1 Hz, 3J = 8.6 Hz, 2 H, H5), 3.64 (dd, 2J = 8.1 Hz, 3J = 2.5 Hz, 2 H, H5‘), 2.24–2.10 (m, 5 H, H1, 1‘, 12), 2.04 (m, 1 H, H12‘), 0.75 (m, 1 H, H11), 0.54 ppm (m, 1 H, H11‘); 13C NMR (C6D6, 150.903 MHz, 295 K): d = 171.5 (C2), 165.9 (C4), 144.9 (C7), 141.1 (C13), 128.9 (C9), 127.5 (C10), 126.1 (C8), 110.6 (C14), 81.0 (C3), 73.5 (C5), 67.8 (C6), 37.0 (C12), 31.1 (C1), 10.3 ppm (C11); HRMS (FAB +): m/z calcd for C24H22N358NiO2 : 497.1613; found: 497.1667. Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
Preparation of (R)-LigPhNi-(iso)supermesityl (7 a) A solution of 1-bromo-2,4,6-tri(tert-butyl)benzene (47 mg, 0.144 mg, 1 equiv) in THF (5 mL) was added to a solution of the nickel(I) complex 4 a (127 mg, 0.287 mmol) in THF (2 mL), and was stirred for 2 h. The solvents were removed and the residue was treated with pentane, stirred for 30 min and filtered. After removal of the solvents, the product was obtained as an orange solid in 45 % yield (90 mg). 1H NMR (C6D6, 600.130 MHz, 295 K): d = 7.61 (d, 4 J = 1.6 Hz, 2 H, H16), 7.34–7.21 (m, 4 H, H8), 7.32 (m, 1 H, H18), 7.14 (m, 4 H, H9), 7.02 (t, 3J = 7.4 Hz, 2 H, H10), 5.10 (s, 2 H, H3), 4.73 (dd, 3 J = 8.5 Hz, 3J = 2.2 Hz, 2 H, H6), 3.48 (dd, 2J = 7.6 Hz, 3J = 2.3 Hz, 2 H, H5), 3.35–3.15 (m, 2 H, H5‘), 2.71 (s, 3 H, H13), 2.27 (m, 4 H, H1, 1‘), 1.40 (s, 18 H, H20), 1.18 (d, 2J = 9.2 Hz, 1 H, H11), 1.07 (d, 2J = 9.2 Hz, 1 H, H11’), 0.77 ppm (s, 3 H, H14); 13C NMR (C6D6, 150.903 MHz, 295 K): d = 170.8 (C2), 165.0 (C4), 153.5 (C15), 149.4 (C17), 145.1 (C7), 129.0 (C9), 127.6 (C10), 126.4 (C8), 121.4 (C16), 118.8 (C18), 80.5 (C3), 73.5 (C5), 69.8 (C6), 42.8 (C12), 35.1 (C13), 34.2 (C19), 31.9 (C20), 30.9 (C1), 29.1 (C14), 20.2 ppm (C11); HRMS (DART +): m/z calcd for C42H52N358NiO2 : 688.3413; found: 688.3428; elemental analysis calcd (%) for C42H41N3NiO2 : C 73.26, H 7.47, N 6.10; found: C 72.74, H 7.95, N 5.42.
Preparation of geminal dihalides The geminal dihalides used as substrates for the catalysis were prepared following the methodology by Takeda et al.[18] 2,2-Dichloro-1,2,3,4-tetrahydronaphthalene: Yield: 810 mg colorless solid, 47 %.1H NMR (CDCl3, 600.130 MHz, 295 K): d = 7.22–7.12 (m, 3 H, H7, 6, 5), 7.04 (s, 1 H, H8), 3.69 (s, 2 H, H1), 3.10 (t, 3J = 6.6 Hz, 2 H, H4), 2.62 ppm (t, 3J = 6.6 Hz, 2 H, H3); 13C NMR (CDCl3, 150.903 MHz, 295 K): d = 133.1 (C10), 132.5 (C9), 128.9 (C5), 128.7 (C8), 127.1 (C6/7), 126.5 (C6/7), 88.2 (C2), 50.1 (C1), 42.5 (C3), 28.3 ppm (C4); HR-MS (EI +): m/z calcd for C10H1035L2 : 200.0160; found: 200.0151; elemental analysis calcd (%) for C10H10Cl2 : C 59.73, H 5.01; found: C 59.86, H 5.05.
General procedure for the catalytic conversion of geminal dichlorides using LiEt3BH as reductant A solution of the catalyst (7.5 mol % in 0.2 mL THF) was slowly added to a solution of the geminal dichloride (0.099 mmol) and LiEt3BH (0.20 mol) in THF (0.5 mL) at the indicated temperature. After the given time, the reaction was quenched using a saturated NH4Cl solution and the reaction products were extracted with pentane (3 1 mL). After removal of the volatiles, the crude was dissolved in a pentane/diethyl ether (9:1) mixture and flushed through a silica plug (washed with 3 1 mL of the 9:1 mixture). After removal of the solvents, the product was dissolved in CDCl3 and 1,4-dimethoxybenzene as internal standard was added to determine the yield of the reaction. GC analysis was performed to determine the enantiomeric excess of the product.
General procedure for the catalytic conversion of geminal dibromides using LiEt3BH as reductant LiEt3BH (0.6 mL of 1.0 m THF solution, 0.60 mol) was added to a solution of the catalyst (9.9 mg, 7.5 mol %) in THF (1.2 mL), and cooled to the indicated temperature. A solution of the dibromide (0.29 mmol in 0.6 mL) was added slowly and stirred for the given time. The reaction mixture was treated using the work-up procedure and analytic methods described above.
9663
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper Determination of the enantiomeric excess by chiral GC analysis Fused Silica Capillary GC Column: Astec Chiraldex G-TA (2,6-di-Opentyl-3-trifluoroacetyl derivative of g-cyclodextrin); Dimension: 50 m 0.25 mm; Film thickness: 0.12 mm; Carrier gas: He. For a detailed description of the methodologies used see the Supporting Information.
ods;[23] 4 a: direct methods with dual-space recycling;[24] 5 a: charge flip.[25] Refinement: full-matrix least squares methods based on F2 ; all non-hydrogen atoms anisotropic, hydrogen atoms (except the deuterides in 3 a, which were refined) at calculated positions (refined riding).[26] CCDC-978128 (3 a), CCDC-978129 (4 a), CCDC-978130 (5 a) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Computational studies (general) The unrestricted DFT-B3LYP computational tool[9] has been employed to model complex 4 a with a 6-311g(d,p) basis set.[10] All the calculations have been carried out with the Gaussian 09 program package.[19] Stationary points were verified by frequency analysis. The Cartesian coordinates of the optimized structure of 4 a are available in the Supporting Information.
Acknowledgements We thank Prof. Dr. M. Enders, Dr. Marion Kerscher, Jan Freudenberg, Mathias Ronellenfitsch and Tim Stçßer for advice and experimental support. We acknowledge funding by the Deutsche Forschungsgemeinschaft (SFB 623, TP B6).
Calculation of EPR parameters The g-values of complex 4 a were calculated using the Orca software (version 2.9.1).[20] Therefore, the optimized geometry above was used as input geometry and the eprnmr feature on the B3LYP/ 6-311G*(d,p) level was applied. Scalar relativistic corrections were applied for the electron structure calculations, and SO interactions were accounted for using the mean-field approx. Spin-orbit mean field (SOMF; incl. both spin-own-orbit and spin-other-orbit interactions).[21] G values (calcd): gx = 2.042, gy = 2.183, gz = 2.216.
Keywords: asymmetric catalysis enantioselectivity · nickel · radicals
Crystal data Complex 3 a: C24H22DN3NiO2, M = 445.17, monoclinic, space group P21, a = 14.39570(10), b = 7.40300(10), c = 19.3928(2) , b = 104.6980(8) 8, V = 1999.09(4) 3, Z = 4, dcalcd = 1.4790 Mg m3, CuKa radiation, l = 1.5418 , m = 1.613 mm1, F000 = 928. T = 115(1) K, q range 3.4 to 72.0 8. Index ranges h, k, l: 17…17, 8…7, 23…23. Reflections measured: 60 179; independent: 7185 [Rint = 0.027]; observed [I > 2s(I)]: 7162. Final R indices [Fo > 4s(Fo)]: R(F) = 0.0220, wR(F2) = 0.0605, GooF = 1.039, residual dens. = 0.36, 0.20 e 3, abs. structure parm. 0.001(8). Complex 4 a: C24H22N3NiO2, M = 443.15, orthorhombic, space group P212 121, a = 8.714(4), b = 10.859(6), c = 20.875(11) , V= 1975.3(18) 3, Z = 4, dcalcd = 1.490 Mg·m3, MoKa radiation, l = 0.71073 , m = 1.009 mm1, F000 = 924. T = 100(1) K, q range 2.0 to 32.2 8. Index ranges h, k, l: 12…12, 16…16, 30…31. Reflections measured: 41198, independent: 6672 [Rint = 0.051], observed. [I > 2s(I)]: 5820. Final R indices [Fo > 4s(Fo)]: R(F) = 0.0327, wR(F2) = 0.0650, GooF = 0.949, residual dens. = 0.47, 0.30 e 3, abs. structure parm. 0.009(5). Complex 5 a·0.5 n-pentane: C35.5H46N4NiO3, M = 635.47, orthorhombic, space group P212121, a = 14.0328(6), b = 15.5952(6), c = 29.2027(15) , V = 6390.8(5) 3, Z = 8, dcalcd = 1.321 Mg·m3, CuKa radiation, l = 1.5418 , m = 1.200 mm1, F000 = 2712. T = 110(1) K, q range 4.0 to 67.9 8. Index ranges h, k, l: 16…16, 18…18, 34…30. Reflections measured: 168 170; independent: 11 472 [Rint = 0.208]; observed [I > 2s(I)]: 8019. Final R indices [Fo > 4s(Fo)]: R(F) = 0.0631, wR(F2) = 0.1481, GooF = 0.966, residual dens. = 0.47, 0.76 e 3, abs. structure parm. 0.03(2). Data collection: Agilent Technologies Supernova-E CCD diffractometer, microfocus X-Ray tube, multilayer mirror optics (complexes 3 a and 5 a) or Bruker AXS Smart 1000 CCD diffractometer, graphite monochromator (complex 4 a). Lorentz, polarization and numerical (3 a, 5 a)/semiempirical absorption correction.[22] Structure solution: 3 a: heavy atom method combined with structure expansion by direct methChem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
9664
·
dehalogenation
·
[1] Selected key references for mechanistic investigations on CC coupling and hydrodehalogenation reactions: a) A. Bakac, J. H. Espenson, J. Am. Chem. Soc. 1986, 108, 719 – 723; b) F. Alonso, I. P. Beletskaya, M. Yus, Chem. Rev. 2002, 102, 4009 – 4092; c) T. J. Anderson, G. D. Jones, D. A. Vicic, J. Am. Chem. Soc. 2004, 126, 8100 – 8101; d) G. D. Jones, J. L. Martin, C. McFarland, O. R. Allen, R. E. Hall, A. D. Haley, R. J. Brandon, T. Konovalova, P. J. Desrochers, P. Pulay, D. A. Vicic, J. Am. Chem. Soc. 2006, 128, 13175 – 13183; e) V. B. Phapale, E. BuÇuel, M. Garca-Iglesias, D. J. Crdenas, Angew. Chem. 2007, 119, 8946 – 8951; Angew. Chem. Int. Ed. 2007, 46, 8790 – 8795; f) X. Hu, Chem. Sci. 2011, 2, 1867 – 1886; g) J. Breitenfeld, J. Ruiz, M. D. Wodrich, X. Hu, J. Am. Chem. Soc. 2013, 135, 12004 – 12012. [2] Selected references for Ni-catalyzed enantioselective CC coupling reactions: a) F. O. Arp, G. C. Fu, J. Am. Chem. Soc. 2005, 127, 10482 – 10483; b) F. Glorius, Angew. Chem. 2008, 120, 8474 – 8476; Angew. Chem. Int. Ed. 2008, 47, 8347 – 8349; c) A. Rudolph, M. Lautens, Angew. Chem. 2009, 121, 2694 – 2708; Angew. Chem. Int. Ed. 2009, 48, 2656 – 2670; d) J. Choi, G. C. Fu, J. Am. Chem. Soc. 2012, 134, 9102 – 9105; e) J. T. Binder, C. J. Cordier, G. C. Fu, J. Am. Chem. Soc. 2012, 134, 17003 – 17006. [3] a) R. Hazard, S. Jaouannet, A. Tallec, Tetrahedron 1982, 38, 93 – 102; b) H.-U. Blaser, S. K. Boyer, U. Pittelkow, Tetrahedron: Asymmetry 1991, 2, 721 – 732; c) M. F. Kuehnel, T. Schlçder, S. Riedel, B. Nieto-Ortega, F. J. Ramrez, J. T. Lpez Navarrete, J. Casado, D. Lentz, Angew. Chem. 2012, 124, 2261 – 2263; Angew. Chem. Int. Ed. 2012, 51, 2218 – 2220. [4] a) D. G. Kelley, A. Marchaj, A. Bakac, J. H. Espenson, J. Am. Chem. Soc. 1991, 113, 7583 – 7587; b) B. B. Wayland, G. Poszmik, S. L. Mukerjee, M. Fryd, J. Am. Chem. Soc. 1994, 116, 7943 – 7944. [5] a) C. Mazet, L. H. Gade, Chem. Eur. J. 2003, 9, 1759 – 1767; b) F. Konrad, J. Lloret Fillol, C. Rettenmeier, H. Wadepohl, L. H. Gade, Eur. J. Inorg. Chem. 2009, 4950 – 4961; c) F. Konrad, J. Lloret Fillol, H. Wadepohl, L. H. Gade, Inorg. Chem. 2009, 48, 8523 – 8535. [6] Selected key references for NiI complexes based on N-containing ligands: a) P. L. Holland, T. R. Cundari, L. L. Perez, N. A. Eckert, R. J. Lachicotte, J. Am. Chem. Soc. 2002, 124, 14416 – 14424; b) E. Kogut, A. Zeller, T. H. Warren, T. Strassner, J. Am. Chem. Soc. 2004, 126, 11984 – 11994; c) S. Pfirrmann, C. Limberg, C. Herwig, R. Stçßer, B. Ziemer, Angew. Chem. 2009, 121, 3407 – 3411; Angew. Chem. Int. Ed. 2009, 48, 3357 – 3361; d) S. Wiese, P. Kapoor, K. D. Williams, T. H. Warren, J. Am. Chem. Soc. 2009, 131, 18105 – 18111; e) S. Yao, Y. Xiong, C. Milsmann, E. Bill, S. Pfirrmann, C. Limberg, M. Driess, Chem. Eur. J. 2010, 16, 436 – 439; f) S. Yao, M. Driess, Acc. Chem. Res. 2012, 45, 276 – 287; g) S. Wiese, J. L. McAfee, D. R. Pahls, C. L. McMullin, T. R. Cundari, T. H. Warren, J. Am. Chem. Soc. 2012, 134, 10114 – 10121; h) C. Uyeda, J. C. Peters, Chem. Sci. 2013, 4, 157 – 163; i) B. Horn, C. Limberg, C. Herwig, B. Braun, Chem. Commun. 2013, 49, 10923 – 10925; j) H. Gehring, R. Metzinger, C. 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper
[7]
[8]
[9]
[10]
[11]
[12]
[13] [14]
Herwig, J. Intemann, S. Harder, C. Limberg, Chem. Eur. J. 2013, 19, 1629 – 1636. Selected key references for NiI complexes based on P-containing ligands: a) D. A. Vicic, W. D. Jones, J. Am. Chem. Soc. 1999, 121, 7606 – 7617; b) D. J. Mindiola, G. L. Hillhouse, J. Am. Chem. Soc. 2001, 123, 4623 – 4624; c) R. Melenkivitz, D. J. Mindiola, G. L. Hillhouse, J. Am. Chem. Soc. 2002, 124, 3846 – 3847; d) D. A. Vicic, T. J. Anderson, J. A. Cowan, A. J. Schultz, J. Am. Chem. Soc. 2004, 126, 8132 – 8133; e) Y. Chen, C. Sui-Seng, D. Zargarian, Angew. Chem. 2005, 117, 7899 – 7903; Angew. Chem. Int. Ed. 2005, 44, 7721 – 7725; f) A. L. Keen, M. Doster, S. A. Johnson, J. Am. Chem. Soc. 2007, 129, 810 – 819; g) V. M. Iluc, G. L. Hillhouse, J. Am. Chem. Soc. 2010, 132, 11890 – 11892. a) C. Eaborn, M. S. Hill, P. B. Hitchcock, J. D. Smith, Chem. Commun. 2000, 691 – 692; b) K. D. Kitiachvili, D. J. Mindiola, G. L. Hillhouse, J. Am. Chem. Soc. 2004, 126, 10554 – 10555; c) E. Kogut, H. L. Wiencko, L. Zhang, D. E. Cordeau, T. H. Warren, J. Am. Chem. Soc. 2005, 127, 11248 – 11249; d) N. A. Eckert, A. Dinescu, T. R. Cundari, P. L. Holland, Inorg. Chem. 2005, 44, 7702 – 7704. a) A. D. Becke, Phys. Rev. A 1988, 38, 3098 – 3100; b) B. Miehlich, A. Savin, H. Stoll, H. Preuss, Chem. Phys. Lett. 1989, 157, 200 – 206; c) A. D. Becke, J. Chem. Phys. 1993, 98, 5648 – 5652. a) A. J. H. Wachters, J. Chem. Phys. 1970, 52, 1033 – 1036; b) P. J. Hay, J. Chem. Phys. 1977, 66, 4377 – 4384; c) R. Krishnan, J. S. Binkley, R. Seeger, J. A. Pople, J. Chem. Phys. 1980, 72, 650 – 654; d) A. D. McLean, G. S. Chandler, J. Chem. Phys. 1980, 72, 5639 – 5648; e) C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785 – 789; f) K. Raghavachari, G. W. Trucks, J. Chem. Phys. 1989, 91, 1062 – 1065; g) R. C. Binning, L. A. Curtiss, J. Comput. Chem. 1990, 11, 1206 – 1216; h) M. P. McGrath, L. Radom, J. Chem. Phys. 1991, 94, 511 – 516; i) L. A. Curtiss, M. P. McGrath, J. P. Blaudeau, N. E. Davis, R. C. Binning, L. Radom, J. Chem. Phys. 1995, 103, 6104 – 6113; j) J.-P. Blaudeau, M. P. McGrath, L. A. Curtiss, L. Radom, J. Chem. Phys. 1997, 107, 5016 – 5021. a) H. Buschmann, H.-D. Scharf, N. Hoffmann, P. Esser, Angew. Chem. 1991, 103, 480 – 518; Angew. Chem. Int. Ed. Engl. 1991, 30, 477 – 515; b) T. Gçbel, K. B. Sharpless, Angew. Chem. 1993, 105, 1417 – 1418; Angew. Chem. Int. Ed. Engl. 1993, 32, 1329 – 1331. Nickel(II) chloride itself was found to act as a precatalyst for the hydrodehalogenation, most likely due to the formation of reactive nickel(0) particles under the reaction conditions (therefore see: A. Roy, V. Srinivas, S. Ram, J. A. De Toro, J. P. Goff, J. Appl. Phys. 2006, 100, 094307). J. Breitenfeld, R. Scopelliti, X. Hu, Organometallics 2012, 31, 2128 – 2136. a) G. Brunton, D. Griller, L. R. C. Barclay, K. U. Ingold, J. Am. Chem. Soc. 1976, 98, 6803 – 6811; b) D. Griller, K. U. Ingold, Acc. Chem. Res. 1980, 13, 317 – 323; c) B. C. Childress, A. C. Rice, P. B. Shevlin, J. Org. Chem. 1974, 39, 3056 – 3058; d) D. C. Nonhebel, Chem. Soc. Rev. 1993, 22, 347 – 359; e) D. Zhu, I. Korobkov, P. H. M. Budzelaar, Organometallics 2012, 31, 3958 – 3971.
Chem. Eur. J. 2014, 20, 9657 – 9665
www.chemeurj.org
[15] a) T. Fukuyama, M. Kobayashi, M. T. Rahman, N. Kamata, I. Ryu, Org. Lett. 2008, 10, 533 – 536; b) J. Wang, Z. Zhu, W. Huang, M. Deng, X. Zhou, J. Organomet. Chem. 2008, 693, 2188 – 2192. [16] W. L. F. Armarego, C. L. L. Chai, Purification of Laboratory Chemicals, Elsevier/Butterworth-Heinemann, 2009. [17] G. R. Fulmer, A. J. M. Miller, N. H. Sherden, H. E. Gottlieb, A. Nudelman, B. M. Stoltz, J. E. Bercaw, K. I. Goldberg, Organometallics 2010, 29, 2176 – 2179. [18] T. Takeda, R. Sasaki, S. Yamauchi, T. Fujiwara, Tetrahedron 1997, 53, 557. [19] Gaussian 09, Revision A.02, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, J. E. Peralta., Jr., F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, . Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian, Inc., Wallingford CT, 2009. [20] F. Neese, ORCA: An ab initio, Density Functional and Semiempirical Program Package, Version 2.9.1 (MPI f r Chemische Energiekonversion). [21] F. Neese, J. Chem. Phys. 2001, 115, 11080. [22] a) SAINT, Bruker AXS, Karlsruhe, 1997 – 2011; b) R. H. Blessing, Acta Crystallogr. Sect. A 1995, 51, 33; c) G. M. Sheldrick, SADABS, Bruker AXS, Karlsruhe, 2004 – 2008; d) CrysAlisPro, Agilent Technologies UK Ltd., Oxford 2011;e) SCALE3 ABSPACK, CrysAlisPro, Agilent Technologies UK Ltd., Oxford 2011. [23] a) P. T. Beurskens, G. Beurskens, R. de Gelder, J. M. M. Smits, S. GarciaGranda, R. O. Gould, DIRDIF-2008, Radboud University Nijmegen, The Netherlands, 2008; b) P. T. Beurskens, in Crystallographic Computing 3 (Eds.: G. M. Sheldrick, C. Kr ger, R. Goddard), Clarendon, Oxford, 1985, p. 216. [24] a) G. M. Sheldrick, SHELXD, University of Gçttingen and Bruker Nonius 2000 – 4; b) G. M. Sheldrick, H. A. Hauptman, C. M. Weeks, R. Miller, I. Usn in International Tables for Crystallography, Vol. F (Eds.: M. G. Rossmann, E. Arnold), IUCr/Kluwer, Dordrecht 2001, pp. 333 – 351. [25] a) L. Palatinus, SUPERFLIP, EPF Lausanne, Switzerland 2007; b) L. Palatinus, G. Chapuis, J. Appl. Crystallogr. 2007, 40, 786. [26] a) G. M. Sheldrick, SHELXL-2012, University of Gçttingen, 2013; b) G. M. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112.
Received: April 25, 2014
9665
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
