J Mol Model (2015): DOI 10.1007/s00894-015-2678-1
ORIGINAL PAPER
A computational study on the insertion of CO2 into (PSiP) palladium allyl σ-bond Qin Wang 1 & Cai-Hong Guo 1 & Ying Ren 1 & Hai-Shun Wu 1
Received: 9 February 2015 / Accepted: 7 April 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract The insertion of CO2 into the (PSiP)palladium-allyl bond has been investigated using DFT. Three possible modes of CO2 insertion into (PSiP)Pd-allyl bond have been calculated, that is, direct 1.2-insertion mode, metallo-ene mode, and SE2 mode. The metallo-ene mode is the most favorable via the six-membered ring transition state. The results of calculations are consistent with the regioselectivity observed experimentally. The steric and electronic effects of different phosphine substituents have been evaluated by ONIOM and energy decomposition analysis (EDA) methods. For the phosphine substituents P(i-Pr)2 and PPh2, the contribution of electronic effect is greater than that of steric effect for the CO2 insertion into (PSiP)Pd-allyl bond; while for the phosphine substituent PMe2, the contribution of steric effect is slightly greater than that of electronic effect. Keyword Carbon dioxide . DFT . ONIOM . Palladium . Regioselectivity
Introduction There is much interest in the utilization of carbon dioxide (CO2) as a starting reactant for chemical synthesis [1–3]. Electronic supplementary material The online version of this article (doi:10.1007/s00894-015-2678-1) contains supplementary material, which is available to authorized users. * Cai-Hong Guo [email protected] * Hai-Shun Wu [email protected] 1
School of Chemistry and Materials Science, Shanxi Normal University, Linfen 041004, People’s Republic of China
The major cause for this interest is that CO2 has been realized as the main contributor to the greenhouse effect, which has caused global warming in the atmosphere [4]. Due to the intrinsic inactivity of CO2, the formation of C-C bonds from CO2 encounters many difficulties, but some advances have been made [5–8]. Recently many transition-metal catalyzed carboxylations of less nucleophilic organometallic reactants including allylstannanes [9, 10], allylboranes [11–13], alkenyl- or arylboronic esters [14–16], or organozincs [17, 18] have been reported. Nevertheless, these methodologies often need preparation of such reagents from the comparable organic halides. According to the synthetic method of atom economy, the desirable methodology to obtain the catalytically nucleophilic organometallic reagents is from easily available unsaturated hydrocarbons. However, such transformations were mostly limited to the Ni-catalyzed oxidative of specific unsaturated hydrocarbons [19–21]. Recently, Iwasawa and co-workers reported the carboxylation of allenes using a silyl-pincer palladium catalyst to provide β,γ-unsaturated carboxylic acids (Scheme 1) [22, 23]. The same addition reactions catalyzed by palladium [24] and nickel [25, 26] complexes have been described previously, but these reactions transformed to α,β-unsaturated carboxylic acid compounds. The unusual character of the study by Iwasawa and co-workers was the utilization of a silyl-pincer palladium complex to control the regioselectivity of the transformation and the reactivity of chemical intermediates. There were some computational studies on the chemical mechanism of CO2 insertion into Pd–allyl bonds in the past decade. Wendt and co-workers carried out DFT calculations on insertion of CO2 into the Pd–allyl bond employing a simplified model coordination compound [27]. In 2010, Hazari and co-workers also implemented DFT computations to explore the influences of different ligands (PH3, PMe3, NHC) on CO2 insertion into Pd–allyl bonds [28]. Recently, both Lin’s group and Hazari’s group implemented DFT calculations on
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Scheme 1 Transformation from allenes to β,γ-unsaturated acids
CO2 insertion into allyl-bridged dinuclear palladium complexes with different ligands [29, 30]. So far, only simple model ligands were mostly utilized in theoretical studies of CO2 insertion into Pd–allyl bonds. Moreover, elaborate studies on the system with real-size molecule need to be considered for the close link between available experimental data and computational results. In order to investigate the systems with real-size ligands and probe effect of ligands, we have applied DFT and ONIOM methods to CO2 insertion into (PSiP)Pd–allyl bond.
Computational methods We implemented all calculations in the Gaussian 09 software package [31]. The present investigation was divided into two sections. In the first section, the density functional theory (DFT) was used to explore the mechanism of CO2 insertion into the (PSiP)palladium allyl complex (P=PPh2). All of the molecular geometries were optimized without constraints using M06 [32–34] functional via DFT calculations. Geometry optimizations and frequency calculations were performed with basis set system (BSI). In BSI, we employed LANL2DZ [35, 36] for Pd and 6-31G(d) [37] basis set for other atoms. All the stationary points were verified via frequency calculations. The minima have zero imaginary frequency, and transition states have only one imaginary frequency. The frequency calculations also provide free energies at room temperature, taking account of the entropy effect. Intrinsic reaction coordinate (IRC) [38, 39] was performed for all transition structures to ensure that transition state connects corresponding reactant and product. We performed single point energy calculations for all molecules with a large basis set (BSII) at the M06 level to get the refined energies. In BSII, the quadruple zeta valence def2-QZVP [40] basis set was used for Pd and the 6-311+G(2d,p) basis set was used for other atoms. To get the solvent effect, we carried out singlepoint energy computations with the integral equation
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Scheme 2 Silyl pincer ligand and schematic representation of the ONIOM partition employed in the calculations
formalism polarizable continuum model (IEFPCM) in dimethylformamide (DMF, ε = 37.2). The radii and nonelectrostatic terms were taken from Truhlar and coworker’ universal solvation model (SMD) [41]. In order to confirm the dependability of the chosen theory level, we made specific researches on geometry optimization and energy computations (see Supplementary material). In the second section, the catalytic reaction was investigated using the ONIOM [42–44] method to probe effects of the phosphine substituents. ONIOM computations were performed using the two layer model, a similar partitioning was applied as described earlier [45, 46]. In the ONIOM division, the studied substrates were separated into two layers: high layer and low layer. High layer included CO2, allene, the palladium, phosphorous and silicon atoms, as well as the part of the ligands, as outlined in Scheme 2 by the dashed lines. The rest of the substrates were included into the low layer. The high layer was handled at a reasonably high M06/BSI level. The low layer was handled by the relative low level HF/ LANL2MB method. Consequently, this two-level ONIOM
Scheme 3 Proposed mechanism for the hydrocarboxylation of allene
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Fig. 1 Energetic profiles computed for CO2 insertion into (PSiP)Pd–allyl bond. The relative free energies (kcal mol-1) are provided
was expressed as ONIOM(M06/BSI:HF/LANL2MB) and it was used for geometry and frequency computations. Singlepoint energy calculations were performed at the ONIOM(M06/BSII:M06/LANL2DZ) level by using optimized geometry at the ONIOM(M06/BSI:HF/LANL2MB) level. In order to evaluate the electronic effect and steric effect of the phosphine ligands on reaction energetics, we also undertook an energy decomposition analysis (EDA) [47, 48] of the reactants and transition states in an analogous approach to that performed previously by Morokuma and co-workers. The reliability of geometry and energy calculations was also tested (see Supplementary material).
Results and discussion
1. The insertion of CO2 into the η1-allyl palladium complex leads to palladium carboxylate, which can go through a transmetalation and β-elimination to form the palladium hydride complexes and generate the aluminum salt of the β,γunsaturated carboxylic acid. As described in the Introduction, this article chiefly studies the regioselectivity in Pd(0)prompted carboxylation of allenes. In my opinion, the critical step, which affects the regioselectivity, is the electrophilic insertion of CO2 into the η1-allyl palladium complex. Therefore, we study this step in detail in order to understand the regioselectivity. We examine the insertion of CO2 into the η1-allyl palladium complex 1D. One can anticipate three different styles of transformation between the Pd–allyl bond and CO2 (as shown in Fig. 1): (I) direct 1.2-insertion of CO2 into the Pd–C1 bond
Mechanism of catalytic cycle Iwasawa and co-workers recently reported that the reductive addition of CO2 to allenes using the silyl-pincer palladium catalyst to give β,γ-unsaturated carboxylic acids [22]. Similar addition reactions catalyzed by palladium and nickel complexes have been described previously [24, 25], but these transformations resulted in α,β-unsaturated carboxylic acid derivatives. We proposed a possible mechanism (Scheme 3) on the basis of the experimental and theoretical studies on the carboxylation of alkenes [49, 50]. Palladium pincer complex is transformed into palladium hydride in the presence of the reductant. The subsequent addition of palladium hydride to allene generates the η1-allyl palladium complex
Fig. 2 Potential energy profiles computed for the insertion of CO2 via metallo-ene mode using ONIOM method. The relative electronic energies are offered in kcal mol-1
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[51]; (II) a cyclic transition state in which C3 react with CO2 (type of metallo-ene mode) [52]; (III) an SE2-type reaction, nevertheless when we carry out an intrinsic reaction coordinate calculation, we find that transition state TS(1–4)D does not directly link to the product compound, but instead to a compound with the coordination of the C=C π bond to palladium. Because the reactions investigated here involve gaseous molecules, we use the free energies for our discussion considering the entropy contribution. The relative free energies (ΔG) of TS(1–2)D, TS(1–3)D, 2D, and 3D in the gas phase and solution (in parentheses) were 31.7 (28.8), 21.1 (21.2), −3.5 (−4.4), and −3.1 (−1.9) kcal mol-1, respectively. The additional calculations showed that the solvent effect was small in solution (DMF). So we use the free energies in gas phase in our discussion. The energetic profiles for CO2 insertion via three modes are shown in Fig. 1. The direct 1.2-insertion of CO2 (mode I) proceeds via a four-membered TS(1–2)D, where the break of Pd–C1 bond and the formation of the Pd–O (CO2) and C1–C (CO2) bonds are simultaneous. The activation barrier (ΔG‡, 1D, PPh2) of 1.2-insertion mode is calculated to be 31.7 kcal mol-1. The activation barrier (ΔG‡, 1D, PPh2) of metallo-ene mode (mode II) is calculated to be 21.1 kcal mol-1. This mode proceeds via a six-membered ring transition state using the η1-allyl π bond as the nucleophilic group attacking the C(CO2) atom. In the transition state TS(1–3)D, the η1-allyl group, the carbonyl group of CO2, and the palladium atom compose a structure of six-membered ring. This transition state also requires that C1 atom of the allyl moiety and the O atom of CO2 coordinate to palladium center simultaneously. The SE2 mode (mode III) could be divided into two steps. At the beginning, the C atom of CO2 attacks C–C π bond of η 1 -allyl to form an olefinic intermediate 4D. Subsequently the olefinic compound goes through ligand substitution to get the carboxylate complex 3D. The initial step of C3 SE2 mode is calculated to overcome the high energy barrier of 28.9 kcal mol-1 (ΔG‡, 1D, PPh2). The rearrangement from 4D to 3D proceeds via a low activation energy of 1.4 kcal mol1 . By comparing the energetics of three modes described above, one can find that mode II is preferred. The transformation at C3 leading to β,γ-unsaturated carboxylic acids has considerably lower barrier than transformation at C1 leading Table 1 Activation energy barriers (ΔE‡) for the insertion of CO2, calculated at ONIOM(M06/BSII:M06/LANL2DZ) and ONIOM(M06/ BSI:UFF) TS(1–3) ONIOM (M06/BSII:M06/Lanl2dz) 1A(PH2) 1B(PMe2) 1C(P(i-Pr)2) 1D(PPh2)
7.9 8.4 6.5 5.8
ONIOM(M06/BSII:UFF)
19.7 33.6 18.0
Scheme 4 Schematic illustration of the decomposition analysis applied
to α,β-unsaturated carboxylic acid, which is consistent with the experimental results [22]. Effects of ligand substituents In order to understand the effects of phosphine substituents, we have explored the insertion of CO2 into the η1-allyl palladium complexes 1 with different phosphine substituents (PH2, PMe2, P(i-Pr)2, and PPh2) via mentallo-ene mode. The calculated energy profiles are depicted in Fig. 2 and the calculated relative energies are summarized in Table 1. It can be seen that the insertion of CO2 into Pd–C bond via metallo-ene mode takes place with the activation barriers (ΔE‡) of 7.9, 8.4, 6.5, Table 2 Results of energy decomposition analysis: the contributions of steric and electronic effects of the phosphine substituents on the activation barrier relative to PH2 are given in kcal mol-1 ΔΔE‡ contribution relative to ΔE‡ for PH2
1B(PMe2) 1C(P(i-Pr)2) 1D(PPh2)
Electronic
Steric
−11.3 −27.1 −12.2
11.8 25.7 10.1
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and 5.8 kcal mol-1 for PH2, PMe2, P(i-Pr)2, and PPh2, respectively. Depending on the computed barriers (ΔE‡), the reactivity of the studied compounds reduces in this order: PPh2 > P(i-Pr)2 > PH2 > PMe2. To deeply understand the above-mentioned computed reactivity order, we have performed energy decomposition analysis (EDA) on the basis of ONIOM computations to evaluate the electronic and steric effects of phosphine substituents on reaction energetics [47, 48]. As shown in Scheme 4, the barriers for PX2 (PX2 =PMe2, P(i-Pr)2, PPh2) are compared with those for PH2 in place of the phosphine substituent PX2. Relative to PH2, the activation barriers are then calculated for PX2 with ONIOM approach, using the force field UFF in one calculation for PX2 and a QM method (M06/LANL2DZ) in another calculation. Comparison of the barriers relative to PH2 allows the approximation of the steric (from the UFF calculation) and electronic contributions of the arms PX2 (through comparison with the QM calculation). Scheme 4 and references give further information on this analysis [47, 48], and Table 2 gives the results of the decomposition analysis involved in the metallo-ene mode. Comparison of ONIOM(M06/BSII:UFF) energetics for PMe2, P(i-Pr)2, and PPh2 with the M06/BSII energy for PH2, the activation barriers (ΔE‡) for PMe2, P(i-Pr)2, and PPh2 are increased by 11.8, 25.7, and 10.1 kcal mol-1, respectively. Both the initial compound 1 and the transition state TS(1–3) are destabilized by these steric interactions. The increase in the activation barrier (ΔE‡) at the ONIOM(M06/BSII:UFF) level indicates that the steric interactions destabilize the transition state TS(1–3) greater than the initial compound 1. At this time, we can think about the electronic effect. In the studied system, both the initial compound and the transition state are affected by the interaction between the phosphine substituent and the palladium center. Comparison of the ONIOM(M06/BSII:UFF) and ONIOM(M06/BSII:M06/LANL2DZ) energies has shown that the activation barriers (ΔE‡) for PMe2, P(i-Pr)2, and PPh2 were decreased by 11.3, 27.1, and 12.2 kcal mol-1, respectively. This indicates that the initial compound may be more influenced by electronic effects relative to the transition state. The joint effect of steric and electronic effects of the phosphine substituents results in the increase for PMe2 and the decrease for P(i-Pr)2, and PPh2 in the activation barriers (ΔE‡). The activation barriers (ΔE‡) for PMe2 is increased by 0.5 kcal mol-1, and for P(i-Pr)2, and PPh2 are decreased by 1.4, and 2.1 kcal mol-1, respectively. The insertion of CO2 into (PSiP)palladium allyl complex follows the trend: PPh2 > P(i-Pr)2 > PH2 > PMe2. Applying EDA method, we have obtained the quantitative results of steric and electronic effects. For the phosphine substituents P(i-Pr)2 and PPh2, the contribution of electronic effect is greater than that of steric effect for the CO2 insertion into (PSiP)Pd-allyl bond; while for the phosphine substituent PMe2, the contribution of steric effect is slightly greater than that of electronic effect.
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Conclusions In the present study, the insertion of CO2 into (PSiP)Pd-allyl bond has been investigated theoretically using computational methods: DFT and ONIOM. We have considered three possible modes of CO2 insertion into (PSiP)Pd-allyl bond when phosphine substituent PPh2, that is, direct 1.2-insertion mode, metallo-ene mode, and SE2 mode. The metallo-ene mode is the most favorable via the six-member ring transition state, and the corresponding activation barrier is computed to be 21.1 kcal mol-1 at the level of M06/6-311+G(2d,p) (def2QZVP for Pd). Our computation results are consistent with the experimental product of β,γ-unsaturated carboxylic acids. Calculations by the ONIOM and EDA methods evaluate the steric and electronic effects induced by different phosphine substituents in (PSiP)Pd allyl complexes. As for the CO2 insertion into (PSiP)Pd–allyl bond, the contribution of electronic effect is greater than that of steric effect when the phosphine substituents are P(i-Pr)2 and PPh2, while with the phosphine substituent PMe2, the contribution of steric effect is slightly greater than that of electronic effect.
Acknowledgments This work is financially supported by the National Natural Science Foundation of China (21373131 and 21203115), the Program for New Century Excellent Talents in University (NCET-121035), the Key Project of Chinese Ministry of Education (212022), and the Research Fund for the Doctoral Program of Higher Education (20111404120004). Compliance with ethical standards Conflict of interest The authors declare that they have no conflict of interest.
References 1.
Huang K, Sun CL, Shi ZJ (2011) Transition-metal-catalyzed C-C bond formation through the fixation of carbon dioxide. Chem Soc Rev 40(5):2435–2452 2. Sakakura T, Choi JC, Yasuda H (2007) Transformation of carbon dioxide. Chem Rev 107(6):2365–2387 3. Tsuji Y, Fujihara T (2012) Carbon dioxide as a carbon source in organic transformation: carbon-carbon bond forming reactions by transition-metal catalysts. Chem Commun 48(80): 9956–9964 4. Aresta M (2010) Carbon dioxide as chemical feedstock. Wiley, Weinheim 5. Marcus Y (2005) Solvatochromic probes in supercritical fluids. J Phys Org Chem 18(5):373–384 6. Chiappe C, Pieraccini D (2005) Ionic liquids: solvent properties and organic reactivity. J Phys Org Chem 18(4):275–297 7. Drees M, Cokoja M, Kuhn FE (2012) Recycling CO 2 ? Computational considerations of the activation of CO2 with homogeneous transition metal catalysts. ChemCatChem 4(11):1703– 1712
12
J Mol Model2 1: 2 )5102(
Page 6 of 7 8.
9. 10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
Cheng DJ, Negreiros FR, Apra E, Fortunelli A (2013) Computational approaches to the chemical conversion of carbon dioxide. Chemsuschem 6(6):944–965 Shi M, Nicholas KM (1997) Palladium-catalyzed carboxylation of allyl stannanes. J Am Chem Soc 119(21):5057–5058 Johansson R, Wendt OF (2007) Insertion of CO2 into a palladium allyl bond and a Pd(II) catalysed carboxylation of allyl stannanes. Dalton Trans 4:488–492 Wu J, Hazari N (2011) Palladium catalyzed carboxylation of allylstannanes and boranes using CO2. Chem Commun 47(3): 1069–1071 Hruszkewycz DP, Wu J, Hazari N, Incarvito CD (2011) Palladium(I)-bridging allyl dimers for the catalytic functionalization of CO2. J Am Chem Soc 133(10):3280–3283 Duong HA, Huleatt PB, Tan Q-W, Shuying EL (2013) Regioselective copper-catalyzed carboxylation of allylboronates with carbon dioxide. Org Lett 15(15):4034–4037 Ukai K, Aoki M, Takaya J, Iwasawa N (2006) Rhodium(I)-catalyzed carboxylation of aryl- and alkenylboronic esters with CO2. J Am Chem Soc 128(27):8706–8707 Takaya J, Tadami S, Ukai K, Iwasawa N (2008) Copper(I)-catalyzed carboxylation of aryl- and alkenylboronic esters. Org Lett 10(13):2697–2700 Ohishi T, Nishiura M, Hou Z (2008) Carboxylation of organoboronic esters catalyzed by N-heterocyclic carbene copper(I) complexes. Angew Chem Int Ed 47(31):5792–5795 Yeung CS, Dong VM (2008) Beyond Aresta’s complex: Ni- and Pd-catalyzed organozinc coupling with CO2. J Am Chem Soc 130(25):7826–7827 Ochiai H, Jang M, Hirano K, Yorimitsu H, Shima K (2008) Nickelcatalyzed carboxylation of organozinc reagent with CO2. Org Lett 10(13):2681–2683 Takimoto M, Mori M (2001) Cross-coupling reaction of oxopi-allylnickel complex generated from 1,3-diene under an atmosphere of carbon dioxide. J Am Chem Soc 123(12):2895– 2896 Takimoto M, Nakamura Y, Kimura K, Mori M (2004) Highly enantioselective catalytic carbon dioxide incorporation reaction: Nickel-catalyzed asymmetric carboxylative cyclization of bis-1,3dienes. J Am Chem Soc 126(19):5956–5957 Takimoto M, Kawamura M, Mori M, Sato Y (2011) Nickelpromoted carboxylation/cyclization cascade of allenyl aldehyde under an atmosphere of CO2. Synlett 2011(10):1423–1426 Takaya J, Iwasawa N (2008) Hydrocarboxylation of allenes with CO2 catalyzed by silyl pincer-type palladium complex. J Am Chem Soc 130(46):15254–15255 Takaya J, Sasano K, Iwasawa N (2011) Efficient one-to-one coupling of easily available 1,3-dienes with carbon dioxide. Org Lett 13(7):1698–1701 Tsuda T, Yamamoto T, Saegusa T (1992) Palladium-catalyzed cycloaddition of carbon-dioxide with methoxyallene. J Organomet Chem 429(3):C46–C48 Takimoto M, Kawamura M, Mori M (2003) Nickel(0)-mediated sequential addition of carbon dioxide and aryl aldehydes into terminal allenes. Org Lett 5(15):2599–2601 Takimoto M, Kawamura M, Mori M, Sato Y (2005) Nickelcatalyzed regio- and stereoselective double carboxylation of trimethylsilylallene under an atmosphere of carbon dioxide and its application to the synthesis of chaetomellic acid A anhydride. Synlett 2005(13):2019–2022 Johnson MT, Johansson R, Kondrashov MV, Steyl G, Ahlquist MSG, Roodt A, Wendt OF (2010) Mechanisms of the CO2 insertion into (PCP) palladium allyl and methyl sigma-bonds. A kinetic and computational study. Organometallics 29(16): 3521–3529
28.
29.
30.
31. 32.
33.
34.
35.
36.
37.
38. 39. 40.
41.
42.
43.
44.
45.
46.
47.
Wu J, Green JC, Hazari N, Hruszkewycz DP, Incarvito CD, Schmeier TJ (2010) The reaction of carbon dioxide with palladium-allyl bonds. Organometallics 29(23):6369–6376 Wang M, Fan T, Lin Z (2012) DFT studies on the reaction of CO2 with allyl-bridged dinuclear palladium(I) complexes. Polyhedron 32(1):35–40 Hruszkewycz DP, Wu J, Green JC, Hazari N, Schmeier TJ (2012) Mechanistic studies of the insertion of CO2 into palladium(I) bridging allyl dimers. Organometallics 31(1):470–485 Frisch MJ, Trucks GW, Schlegel HB et al. (2010) Gaussian 09, Revision C.01. Gaussian Inc, Wallingford Zhao Y, Schultz NE, Truhlar DG (2006) Design of density functionals by combining the method of constraint satisfaction with parametrization for thermochemistry, thermochemical kinetics, and noncovalent interactions. J Chem Theory Comput 2(2):364– 382 Zhao Y, Truhlar DG (2006) Density functional for spectroscopy: no long-range self-interaction error, good performance for rydberg and charge-transfer states, and better performance on average than B3LYP for ground states. J Phys Chem A 110(49):13126–13130 Zhao Y, Truhlar DG (2008) The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor Chem Acc 120(1–3):215– 241 Hay PJ, Wadt WR (1985) Abinitio effective core potentials for molecular carculations-potentials for the transition-metal atoms Sc to Hg. J Chem Phys 82(1):270–283 Wadt WR, Hay PJ (1985) Abinitio effective core potentials for molecular calculations-potentials for main group elements Na to Bi. J Chem Phys 82(1):284–298 Harihara PC, Pople JA (1973) Influence of polarization functions on molecular-orbital hydrogenation energies. Theor Chim Acta 28(3):213–222 Fukui K (1970) Formulation of the reaction coordinate. J Phys Chem 74(23):4161–4163 Fukui K (1981) The path of chemical reactions — the IRC approach. Acc Chem Res 14(12):363–368 Weigend F, Furche F, Ahlrichs R (2003) Gaussian basis sets of quadruple zeta valence quality for atoms H–Kr. J Chem Phys 119(24):12753–12762 Marenich AV, Cramer CJ, Truhlar DG (2009) Universal solvation model based on solute electron density and on a continuum model of the solvent defined by the bulk dielectric constant and atomic surface tensions. J Phys Chem B 113(18):6378–6396 Dapprich S, Komaromi I, Byun KS, Morokuma K, Frisch MJ (1999) A new ONIOM implementation in Gaussian98. Part I. The calculation of energies, gradients, vibrational frequencies and electric field derivatives. THEOCHEM 461:1–21 Vreven T, Morokuma K (2000) On the application of the IMOMO (integrated molecular orbital plus molecular orbital) method. J Comput Chem 21(16):1419–1432 Ananikov VP, Szilagyi R, Morokuma K, Musaev DG (2005) Can steric effects induce the mechanism switch in the rhodiumcatalyzed imine boration reaction? A density functional and ONIOM study. Organometallics 24(8):1938–1946 Curet-Arana MC, Emberger GA, Broadbelt LJ, Snurr RQ (2008) Quantum chemical determination of stable intermediates for alkene epoxidation with Mn-porphyrin catalysts. J Mol Catal A Chem 285(1–2):120–127 Carvajal MA, Kozuch S, Shaik S (2009) Factors controlling the selective hydroformylation of internal alkenes to linear aldehydes. 1. The isomerization step. Organometallics 28(13):3656–3665 Ananikov VP, Musaev DG, Morokuma K (2007) Critical effect of phosphane ligands on the mechanism of carbon-carbon bond
J Mol Model (2015): formation involving palladium(II) complexes: a theoretical investigation of reductive elimination from square-planar and T-shaped species. Eur J Inorg Chem 34:5390–5399 48. Ananikov VP, Musaev DG, Morokuma K (2010) Real size of ligands, reactants and catalysts: Studies of structure, reactivity and selectivity by ONIOM and other hybrid computational approaches. J Mol Catal A Chem 324(1–2):104–119 49. Ostapowicz TG, Hoelscher M, Leitner W (2012) Catalytic hydrocarboxylation of olefins with CO2 and H2-a DFT computational analysis. Eur J Inorg Chem 34:5632–5641
Page 7 of 7 12 50.
51. 52.
Schmeier TJ, Hazari N, Incarvito CD, Raskatov JA (2011) Exploring the reactions of CO2 with PCP supported nickel complexes. Chem Commun 47(6):1824–1826 Crabtree RH (2005) The organometallic chemistry of the transition metals. Wiley, Weiheim Davies AG (2000) Metals as surrogates for hydrogen in organic chemistry: anything hydrogen can do, a metal can do better. J Chem Soc Perkin Trans 1(13):1997–2010
ORIGINAL PAPER
A computational study on the insertion of CO2 into (PSiP) palladium allyl σ-bond Qin Wang 1 & Cai-Hong Guo 1 & Ying Ren 1 & Hai-Shun Wu 1
Received: 9 February 2015 / Accepted: 7 April 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract The insertion of CO2 into the (PSiP)palladium-allyl bond has been investigated using DFT. Three possible modes of CO2 insertion into (PSiP)Pd-allyl bond have been calculated, that is, direct 1.2-insertion mode, metallo-ene mode, and SE2 mode. The metallo-ene mode is the most favorable via the six-membered ring transition state. The results of calculations are consistent with the regioselectivity observed experimentally. The steric and electronic effects of different phosphine substituents have been evaluated by ONIOM and energy decomposition analysis (EDA) methods. For the phosphine substituents P(i-Pr)2 and PPh2, the contribution of electronic effect is greater than that of steric effect for the CO2 insertion into (PSiP)Pd-allyl bond; while for the phosphine substituent PMe2, the contribution of steric effect is slightly greater than that of electronic effect. Keyword Carbon dioxide . DFT . ONIOM . Palladium . Regioselectivity
Introduction There is much interest in the utilization of carbon dioxide (CO2) as a starting reactant for chemical synthesis [1–3]. Electronic supplementary material The online version of this article (doi:10.1007/s00894-015-2678-1) contains supplementary material, which is available to authorized users. * Cai-Hong Guo [email protected] * Hai-Shun Wu [email protected] 1
School of Chemistry and Materials Science, Shanxi Normal University, Linfen 041004, People’s Republic of China
The major cause for this interest is that CO2 has been realized as the main contributor to the greenhouse effect, which has caused global warming in the atmosphere [4]. Due to the intrinsic inactivity of CO2, the formation of C-C bonds from CO2 encounters many difficulties, but some advances have been made [5–8]. Recently many transition-metal catalyzed carboxylations of less nucleophilic organometallic reactants including allylstannanes [9, 10], allylboranes [11–13], alkenyl- or arylboronic esters [14–16], or organozincs [17, 18] have been reported. Nevertheless, these methodologies often need preparation of such reagents from the comparable organic halides. According to the synthetic method of atom economy, the desirable methodology to obtain the catalytically nucleophilic organometallic reagents is from easily available unsaturated hydrocarbons. However, such transformations were mostly limited to the Ni-catalyzed oxidative of specific unsaturated hydrocarbons [19–21]. Recently, Iwasawa and co-workers reported the carboxylation of allenes using a silyl-pincer palladium catalyst to provide β,γ-unsaturated carboxylic acids (Scheme 1) [22, 23]. The same addition reactions catalyzed by palladium [24] and nickel [25, 26] complexes have been described previously, but these reactions transformed to α,β-unsaturated carboxylic acid compounds. The unusual character of the study by Iwasawa and co-workers was the utilization of a silyl-pincer palladium complex to control the regioselectivity of the transformation and the reactivity of chemical intermediates. There were some computational studies on the chemical mechanism of CO2 insertion into Pd–allyl bonds in the past decade. Wendt and co-workers carried out DFT calculations on insertion of CO2 into the Pd–allyl bond employing a simplified model coordination compound [27]. In 2010, Hazari and co-workers also implemented DFT computations to explore the influences of different ligands (PH3, PMe3, NHC) on CO2 insertion into Pd–allyl bonds [28]. Recently, both Lin’s group and Hazari’s group implemented DFT calculations on
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Scheme 1 Transformation from allenes to β,γ-unsaturated acids
CO2 insertion into allyl-bridged dinuclear palladium complexes with different ligands [29, 30]. So far, only simple model ligands were mostly utilized in theoretical studies of CO2 insertion into Pd–allyl bonds. Moreover, elaborate studies on the system with real-size molecule need to be considered for the close link between available experimental data and computational results. In order to investigate the systems with real-size ligands and probe effect of ligands, we have applied DFT and ONIOM methods to CO2 insertion into (PSiP)Pd–allyl bond.
Computational methods We implemented all calculations in the Gaussian 09 software package [31]. The present investigation was divided into two sections. In the first section, the density functional theory (DFT) was used to explore the mechanism of CO2 insertion into the (PSiP)palladium allyl complex (P=PPh2). All of the molecular geometries were optimized without constraints using M06 [32–34] functional via DFT calculations. Geometry optimizations and frequency calculations were performed with basis set system (BSI). In BSI, we employed LANL2DZ [35, 36] for Pd and 6-31G(d) [37] basis set for other atoms. All the stationary points were verified via frequency calculations. The minima have zero imaginary frequency, and transition states have only one imaginary frequency. The frequency calculations also provide free energies at room temperature, taking account of the entropy effect. Intrinsic reaction coordinate (IRC) [38, 39] was performed for all transition structures to ensure that transition state connects corresponding reactant and product. We performed single point energy calculations for all molecules with a large basis set (BSII) at the M06 level to get the refined energies. In BSII, the quadruple zeta valence def2-QZVP [40] basis set was used for Pd and the 6-311+G(2d,p) basis set was used for other atoms. To get the solvent effect, we carried out singlepoint energy computations with the integral equation
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Scheme 2 Silyl pincer ligand and schematic representation of the ONIOM partition employed in the calculations
formalism polarizable continuum model (IEFPCM) in dimethylformamide (DMF, ε = 37.2). The radii and nonelectrostatic terms were taken from Truhlar and coworker’ universal solvation model (SMD) [41]. In order to confirm the dependability of the chosen theory level, we made specific researches on geometry optimization and energy computations (see Supplementary material). In the second section, the catalytic reaction was investigated using the ONIOM [42–44] method to probe effects of the phosphine substituents. ONIOM computations were performed using the two layer model, a similar partitioning was applied as described earlier [45, 46]. In the ONIOM division, the studied substrates were separated into two layers: high layer and low layer. High layer included CO2, allene, the palladium, phosphorous and silicon atoms, as well as the part of the ligands, as outlined in Scheme 2 by the dashed lines. The rest of the substrates were included into the low layer. The high layer was handled at a reasonably high M06/BSI level. The low layer was handled by the relative low level HF/ LANL2MB method. Consequently, this two-level ONIOM
Scheme 3 Proposed mechanism for the hydrocarboxylation of allene
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Fig. 1 Energetic profiles computed for CO2 insertion into (PSiP)Pd–allyl bond. The relative free energies (kcal mol-1) are provided
was expressed as ONIOM(M06/BSI:HF/LANL2MB) and it was used for geometry and frequency computations. Singlepoint energy calculations were performed at the ONIOM(M06/BSII:M06/LANL2DZ) level by using optimized geometry at the ONIOM(M06/BSI:HF/LANL2MB) level. In order to evaluate the electronic effect and steric effect of the phosphine ligands on reaction energetics, we also undertook an energy decomposition analysis (EDA) [47, 48] of the reactants and transition states in an analogous approach to that performed previously by Morokuma and co-workers. The reliability of geometry and energy calculations was also tested (see Supplementary material).
Results and discussion
1. The insertion of CO2 into the η1-allyl palladium complex leads to palladium carboxylate, which can go through a transmetalation and β-elimination to form the palladium hydride complexes and generate the aluminum salt of the β,γunsaturated carboxylic acid. As described in the Introduction, this article chiefly studies the regioselectivity in Pd(0)prompted carboxylation of allenes. In my opinion, the critical step, which affects the regioselectivity, is the electrophilic insertion of CO2 into the η1-allyl palladium complex. Therefore, we study this step in detail in order to understand the regioselectivity. We examine the insertion of CO2 into the η1-allyl palladium complex 1D. One can anticipate three different styles of transformation between the Pd–allyl bond and CO2 (as shown in Fig. 1): (I) direct 1.2-insertion of CO2 into the Pd–C1 bond
Mechanism of catalytic cycle Iwasawa and co-workers recently reported that the reductive addition of CO2 to allenes using the silyl-pincer palladium catalyst to give β,γ-unsaturated carboxylic acids [22]. Similar addition reactions catalyzed by palladium and nickel complexes have been described previously [24, 25], but these transformations resulted in α,β-unsaturated carboxylic acid derivatives. We proposed a possible mechanism (Scheme 3) on the basis of the experimental and theoretical studies on the carboxylation of alkenes [49, 50]. Palladium pincer complex is transformed into palladium hydride in the presence of the reductant. The subsequent addition of palladium hydride to allene generates the η1-allyl palladium complex
Fig. 2 Potential energy profiles computed for the insertion of CO2 via metallo-ene mode using ONIOM method. The relative electronic energies are offered in kcal mol-1
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[51]; (II) a cyclic transition state in which C3 react with CO2 (type of metallo-ene mode) [52]; (III) an SE2-type reaction, nevertheless when we carry out an intrinsic reaction coordinate calculation, we find that transition state TS(1–4)D does not directly link to the product compound, but instead to a compound with the coordination of the C=C π bond to palladium. Because the reactions investigated here involve gaseous molecules, we use the free energies for our discussion considering the entropy contribution. The relative free energies (ΔG) of TS(1–2)D, TS(1–3)D, 2D, and 3D in the gas phase and solution (in parentheses) were 31.7 (28.8), 21.1 (21.2), −3.5 (−4.4), and −3.1 (−1.9) kcal mol-1, respectively. The additional calculations showed that the solvent effect was small in solution (DMF). So we use the free energies in gas phase in our discussion. The energetic profiles for CO2 insertion via three modes are shown in Fig. 1. The direct 1.2-insertion of CO2 (mode I) proceeds via a four-membered TS(1–2)D, where the break of Pd–C1 bond and the formation of the Pd–O (CO2) and C1–C (CO2) bonds are simultaneous. The activation barrier (ΔG‡, 1D, PPh2) of 1.2-insertion mode is calculated to be 31.7 kcal mol-1. The activation barrier (ΔG‡, 1D, PPh2) of metallo-ene mode (mode II) is calculated to be 21.1 kcal mol-1. This mode proceeds via a six-membered ring transition state using the η1-allyl π bond as the nucleophilic group attacking the C(CO2) atom. In the transition state TS(1–3)D, the η1-allyl group, the carbonyl group of CO2, and the palladium atom compose a structure of six-membered ring. This transition state also requires that C1 atom of the allyl moiety and the O atom of CO2 coordinate to palladium center simultaneously. The SE2 mode (mode III) could be divided into two steps. At the beginning, the C atom of CO2 attacks C–C π bond of η 1 -allyl to form an olefinic intermediate 4D. Subsequently the olefinic compound goes through ligand substitution to get the carboxylate complex 3D. The initial step of C3 SE2 mode is calculated to overcome the high energy barrier of 28.9 kcal mol-1 (ΔG‡, 1D, PPh2). The rearrangement from 4D to 3D proceeds via a low activation energy of 1.4 kcal mol1 . By comparing the energetics of three modes described above, one can find that mode II is preferred. The transformation at C3 leading to β,γ-unsaturated carboxylic acids has considerably lower barrier than transformation at C1 leading Table 1 Activation energy barriers (ΔE‡) for the insertion of CO2, calculated at ONIOM(M06/BSII:M06/LANL2DZ) and ONIOM(M06/ BSI:UFF) TS(1–3) ONIOM (M06/BSII:M06/Lanl2dz) 1A(PH2) 1B(PMe2) 1C(P(i-Pr)2) 1D(PPh2)
7.9 8.4 6.5 5.8
ONIOM(M06/BSII:UFF)
19.7 33.6 18.0
Scheme 4 Schematic illustration of the decomposition analysis applied
to α,β-unsaturated carboxylic acid, which is consistent with the experimental results [22]. Effects of ligand substituents In order to understand the effects of phosphine substituents, we have explored the insertion of CO2 into the η1-allyl palladium complexes 1 with different phosphine substituents (PH2, PMe2, P(i-Pr)2, and PPh2) via mentallo-ene mode. The calculated energy profiles are depicted in Fig. 2 and the calculated relative energies are summarized in Table 1. It can be seen that the insertion of CO2 into Pd–C bond via metallo-ene mode takes place with the activation barriers (ΔE‡) of 7.9, 8.4, 6.5, Table 2 Results of energy decomposition analysis: the contributions of steric and electronic effects of the phosphine substituents on the activation barrier relative to PH2 are given in kcal mol-1 ΔΔE‡ contribution relative to ΔE‡ for PH2
1B(PMe2) 1C(P(i-Pr)2) 1D(PPh2)
Electronic
Steric
−11.3 −27.1 −12.2
11.8 25.7 10.1
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and 5.8 kcal mol-1 for PH2, PMe2, P(i-Pr)2, and PPh2, respectively. Depending on the computed barriers (ΔE‡), the reactivity of the studied compounds reduces in this order: PPh2 > P(i-Pr)2 > PH2 > PMe2. To deeply understand the above-mentioned computed reactivity order, we have performed energy decomposition analysis (EDA) on the basis of ONIOM computations to evaluate the electronic and steric effects of phosphine substituents on reaction energetics [47, 48]. As shown in Scheme 4, the barriers for PX2 (PX2 =PMe2, P(i-Pr)2, PPh2) are compared with those for PH2 in place of the phosphine substituent PX2. Relative to PH2, the activation barriers are then calculated for PX2 with ONIOM approach, using the force field UFF in one calculation for PX2 and a QM method (M06/LANL2DZ) in another calculation. Comparison of the barriers relative to PH2 allows the approximation of the steric (from the UFF calculation) and electronic contributions of the arms PX2 (through comparison with the QM calculation). Scheme 4 and references give further information on this analysis [47, 48], and Table 2 gives the results of the decomposition analysis involved in the metallo-ene mode. Comparison of ONIOM(M06/BSII:UFF) energetics for PMe2, P(i-Pr)2, and PPh2 with the M06/BSII energy for PH2, the activation barriers (ΔE‡) for PMe2, P(i-Pr)2, and PPh2 are increased by 11.8, 25.7, and 10.1 kcal mol-1, respectively. Both the initial compound 1 and the transition state TS(1–3) are destabilized by these steric interactions. The increase in the activation barrier (ΔE‡) at the ONIOM(M06/BSII:UFF) level indicates that the steric interactions destabilize the transition state TS(1–3) greater than the initial compound 1. At this time, we can think about the electronic effect. In the studied system, both the initial compound and the transition state are affected by the interaction between the phosphine substituent and the palladium center. Comparison of the ONIOM(M06/BSII:UFF) and ONIOM(M06/BSII:M06/LANL2DZ) energies has shown that the activation barriers (ΔE‡) for PMe2, P(i-Pr)2, and PPh2 were decreased by 11.3, 27.1, and 12.2 kcal mol-1, respectively. This indicates that the initial compound may be more influenced by electronic effects relative to the transition state. The joint effect of steric and electronic effects of the phosphine substituents results in the increase for PMe2 and the decrease for P(i-Pr)2, and PPh2 in the activation barriers (ΔE‡). The activation barriers (ΔE‡) for PMe2 is increased by 0.5 kcal mol-1, and for P(i-Pr)2, and PPh2 are decreased by 1.4, and 2.1 kcal mol-1, respectively. The insertion of CO2 into (PSiP)palladium allyl complex follows the trend: PPh2 > P(i-Pr)2 > PH2 > PMe2. Applying EDA method, we have obtained the quantitative results of steric and electronic effects. For the phosphine substituents P(i-Pr)2 and PPh2, the contribution of electronic effect is greater than that of steric effect for the CO2 insertion into (PSiP)Pd-allyl bond; while for the phosphine substituent PMe2, the contribution of steric effect is slightly greater than that of electronic effect.
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Conclusions In the present study, the insertion of CO2 into (PSiP)Pd-allyl bond has been investigated theoretically using computational methods: DFT and ONIOM. We have considered three possible modes of CO2 insertion into (PSiP)Pd-allyl bond when phosphine substituent PPh2, that is, direct 1.2-insertion mode, metallo-ene mode, and SE2 mode. The metallo-ene mode is the most favorable via the six-member ring transition state, and the corresponding activation barrier is computed to be 21.1 kcal mol-1 at the level of M06/6-311+G(2d,p) (def2QZVP for Pd). Our computation results are consistent with the experimental product of β,γ-unsaturated carboxylic acids. Calculations by the ONIOM and EDA methods evaluate the steric and electronic effects induced by different phosphine substituents in (PSiP)Pd allyl complexes. As for the CO2 insertion into (PSiP)Pd–allyl bond, the contribution of electronic effect is greater than that of steric effect when the phosphine substituents are P(i-Pr)2 and PPh2, while with the phosphine substituent PMe2, the contribution of steric effect is slightly greater than that of electronic effect.
Acknowledgments This work is financially supported by the National Natural Science Foundation of China (21373131 and 21203115), the Program for New Century Excellent Talents in University (NCET-121035), the Key Project of Chinese Ministry of Education (212022), and the Research Fund for the Doctoral Program of Higher Education (20111404120004). Compliance with ethical standards Conflict of interest The authors declare that they have no conflict of interest.
References 1.
Huang K, Sun CL, Shi ZJ (2011) Transition-metal-catalyzed C-C bond formation through the fixation of carbon dioxide. Chem Soc Rev 40(5):2435–2452 2. Sakakura T, Choi JC, Yasuda H (2007) Transformation of carbon dioxide. Chem Rev 107(6):2365–2387 3. Tsuji Y, Fujihara T (2012) Carbon dioxide as a carbon source in organic transformation: carbon-carbon bond forming reactions by transition-metal catalysts. Chem Commun 48(80): 9956–9964 4. Aresta M (2010) Carbon dioxide as chemical feedstock. Wiley, Weinheim 5. Marcus Y (2005) Solvatochromic probes in supercritical fluids. J Phys Org Chem 18(5):373–384 6. Chiappe C, Pieraccini D (2005) Ionic liquids: solvent properties and organic reactivity. J Phys Org Chem 18(4):275–297 7. Drees M, Cokoja M, Kuhn FE (2012) Recycling CO 2 ? Computational considerations of the activation of CO2 with homogeneous transition metal catalysts. ChemCatChem 4(11):1703– 1712
12
J Mol Model2 1: 2 )5102(
Page 6 of 7 8.
9. 10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
Cheng DJ, Negreiros FR, Apra E, Fortunelli A (2013) Computational approaches to the chemical conversion of carbon dioxide. Chemsuschem 6(6):944–965 Shi M, Nicholas KM (1997) Palladium-catalyzed carboxylation of allyl stannanes. J Am Chem Soc 119(21):5057–5058 Johansson R, Wendt OF (2007) Insertion of CO2 into a palladium allyl bond and a Pd(II) catalysed carboxylation of allyl stannanes. Dalton Trans 4:488–492 Wu J, Hazari N (2011) Palladium catalyzed carboxylation of allylstannanes and boranes using CO2. Chem Commun 47(3): 1069–1071 Hruszkewycz DP, Wu J, Hazari N, Incarvito CD (2011) Palladium(I)-bridging allyl dimers for the catalytic functionalization of CO2. J Am Chem Soc 133(10):3280–3283 Duong HA, Huleatt PB, Tan Q-W, Shuying EL (2013) Regioselective copper-catalyzed carboxylation of allylboronates with carbon dioxide. Org Lett 15(15):4034–4037 Ukai K, Aoki M, Takaya J, Iwasawa N (2006) Rhodium(I)-catalyzed carboxylation of aryl- and alkenylboronic esters with CO2. J Am Chem Soc 128(27):8706–8707 Takaya J, Tadami S, Ukai K, Iwasawa N (2008) Copper(I)-catalyzed carboxylation of aryl- and alkenylboronic esters. Org Lett 10(13):2697–2700 Ohishi T, Nishiura M, Hou Z (2008) Carboxylation of organoboronic esters catalyzed by N-heterocyclic carbene copper(I) complexes. Angew Chem Int Ed 47(31):5792–5795 Yeung CS, Dong VM (2008) Beyond Aresta’s complex: Ni- and Pd-catalyzed organozinc coupling with CO2. J Am Chem Soc 130(25):7826–7827 Ochiai H, Jang M, Hirano K, Yorimitsu H, Shima K (2008) Nickelcatalyzed carboxylation of organozinc reagent with CO2. Org Lett 10(13):2681–2683 Takimoto M, Mori M (2001) Cross-coupling reaction of oxopi-allylnickel complex generated from 1,3-diene under an atmosphere of carbon dioxide. J Am Chem Soc 123(12):2895– 2896 Takimoto M, Nakamura Y, Kimura K, Mori M (2004) Highly enantioselective catalytic carbon dioxide incorporation reaction: Nickel-catalyzed asymmetric carboxylative cyclization of bis-1,3dienes. J Am Chem Soc 126(19):5956–5957 Takimoto M, Kawamura M, Mori M, Sato Y (2011) Nickelpromoted carboxylation/cyclization cascade of allenyl aldehyde under an atmosphere of CO2. Synlett 2011(10):1423–1426 Takaya J, Iwasawa N (2008) Hydrocarboxylation of allenes with CO2 catalyzed by silyl pincer-type palladium complex. J Am Chem Soc 130(46):15254–15255 Takaya J, Sasano K, Iwasawa N (2011) Efficient one-to-one coupling of easily available 1,3-dienes with carbon dioxide. Org Lett 13(7):1698–1701 Tsuda T, Yamamoto T, Saegusa T (1992) Palladium-catalyzed cycloaddition of carbon-dioxide with methoxyallene. J Organomet Chem 429(3):C46–C48 Takimoto M, Kawamura M, Mori M (2003) Nickel(0)-mediated sequential addition of carbon dioxide and aryl aldehydes into terminal allenes. Org Lett 5(15):2599–2601 Takimoto M, Kawamura M, Mori M, Sato Y (2005) Nickelcatalyzed regio- and stereoselective double carboxylation of trimethylsilylallene under an atmosphere of carbon dioxide and its application to the synthesis of chaetomellic acid A anhydride. Synlett 2005(13):2019–2022 Johnson MT, Johansson R, Kondrashov MV, Steyl G, Ahlquist MSG, Roodt A, Wendt OF (2010) Mechanisms of the CO2 insertion into (PCP) palladium allyl and methyl sigma-bonds. A kinetic and computational study. Organometallics 29(16): 3521–3529
28.
29.
30.
31. 32.
33.
34.
35.
36.
37.
38. 39. 40.
41.
42.
43.
44.
45.
46.
47.
Wu J, Green JC, Hazari N, Hruszkewycz DP, Incarvito CD, Schmeier TJ (2010) The reaction of carbon dioxide with palladium-allyl bonds. Organometallics 29(23):6369–6376 Wang M, Fan T, Lin Z (2012) DFT studies on the reaction of CO2 with allyl-bridged dinuclear palladium(I) complexes. Polyhedron 32(1):35–40 Hruszkewycz DP, Wu J, Green JC, Hazari N, Schmeier TJ (2012) Mechanistic studies of the insertion of CO2 into palladium(I) bridging allyl dimers. Organometallics 31(1):470–485 Frisch MJ, Trucks GW, Schlegel HB et al. (2010) Gaussian 09, Revision C.01. Gaussian Inc, Wallingford Zhao Y, Schultz NE, Truhlar DG (2006) Design of density functionals by combining the method of constraint satisfaction with parametrization for thermochemistry, thermochemical kinetics, and noncovalent interactions. J Chem Theory Comput 2(2):364– 382 Zhao Y, Truhlar DG (2006) Density functional for spectroscopy: no long-range self-interaction error, good performance for rydberg and charge-transfer states, and better performance on average than B3LYP for ground states. J Phys Chem A 110(49):13126–13130 Zhao Y, Truhlar DG (2008) The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor Chem Acc 120(1–3):215– 241 Hay PJ, Wadt WR (1985) Abinitio effective core potentials for molecular carculations-potentials for the transition-metal atoms Sc to Hg. J Chem Phys 82(1):270–283 Wadt WR, Hay PJ (1985) Abinitio effective core potentials for molecular calculations-potentials for main group elements Na to Bi. J Chem Phys 82(1):284–298 Harihara PC, Pople JA (1973) Influence of polarization functions on molecular-orbital hydrogenation energies. Theor Chim Acta 28(3):213–222 Fukui K (1970) Formulation of the reaction coordinate. J Phys Chem 74(23):4161–4163 Fukui K (1981) The path of chemical reactions — the IRC approach. Acc Chem Res 14(12):363–368 Weigend F, Furche F, Ahlrichs R (2003) Gaussian basis sets of quadruple zeta valence quality for atoms H–Kr. J Chem Phys 119(24):12753–12762 Marenich AV, Cramer CJ, Truhlar DG (2009) Universal solvation model based on solute electron density and on a continuum model of the solvent defined by the bulk dielectric constant and atomic surface tensions. J Phys Chem B 113(18):6378–6396 Dapprich S, Komaromi I, Byun KS, Morokuma K, Frisch MJ (1999) A new ONIOM implementation in Gaussian98. Part I. The calculation of energies, gradients, vibrational frequencies and electric field derivatives. THEOCHEM 461:1–21 Vreven T, Morokuma K (2000) On the application of the IMOMO (integrated molecular orbital plus molecular orbital) method. J Comput Chem 21(16):1419–1432 Ananikov VP, Szilagyi R, Morokuma K, Musaev DG (2005) Can steric effects induce the mechanism switch in the rhodiumcatalyzed imine boration reaction? A density functional and ONIOM study. Organometallics 24(8):1938–1946 Curet-Arana MC, Emberger GA, Broadbelt LJ, Snurr RQ (2008) Quantum chemical determination of stable intermediates for alkene epoxidation with Mn-porphyrin catalysts. J Mol Catal A Chem 285(1–2):120–127 Carvajal MA, Kozuch S, Shaik S (2009) Factors controlling the selective hydroformylation of internal alkenes to linear aldehydes. 1. The isomerization step. Organometallics 28(13):3656–3665 Ananikov VP, Musaev DG, Morokuma K (2007) Critical effect of phosphane ligands on the mechanism of carbon-carbon bond
J Mol Model (2015): formation involving palladium(II) complexes: a theoretical investigation of reductive elimination from square-planar and T-shaped species. Eur J Inorg Chem 34:5390–5399 48. Ananikov VP, Musaev DG, Morokuma K (2010) Real size of ligands, reactants and catalysts: Studies of structure, reactivity and selectivity by ONIOM and other hybrid computational approaches. J Mol Catal A Chem 324(1–2):104–119 49. Ostapowicz TG, Hoelscher M, Leitner W (2012) Catalytic hydrocarboxylation of olefins with CO2 and H2-a DFT computational analysis. Eur J Inorg Chem 34:5632–5641
Page 7 of 7 12 50.
51. 52.
Schmeier TJ, Hazari N, Incarvito CD, Raskatov JA (2011) Exploring the reactions of CO2 with PCP supported nickel complexes. Chem Commun 47(6):1824–1826 Crabtree RH (2005) The organometallic chemistry of the transition metals. Wiley, Weiheim Davies AG (2000) Metals as surrogates for hydrogen in organic chemistry: anything hydrogen can do, a metal can do better. J Chem Soc Perkin Trans 1(13):1997–2010
