Bisamino(diphosphonite) with dangling olefin functionalities: synthesis, metal chemistry and catalytic utility of Rh(I) and Pd(II) complexes in hydroformylation and Suzuki-Miyaura reactions.

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Bisamino(diphosphonite) with dangling olefin functionalities: synthesis, metal chemistry and catalytic utility of RhI and PdII complexes in hydroformylation and Suzuki–Miyaura reactions† Susmita Naik,a Maruthai Kumaravel,a Joel T. Magueb and Maravanji S. Balakrishna*a Bisamino(diphosphonite), p-C6H4{N{P(OC6H4C3H5-o)2}2}2 (1), was prepared by reacting p-C6H4{N(PCl2)2}2 with four equivalents of o-allylphenol in 85% yield. Compound 1 on treatment with [M(CO)4(HNC5H10)2] (M = Mo or W) gave cis-[{M(CO)4}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (2, M = Mo; 3, M = W). The reaction of 1 with [Fe(η5-C5H5)(CO)2]2 yielded the complex [{Fe(η5-C5H5)(μ-CO)}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (4). Treatment of 1 with Fe(CO)5 furnished a mononuclear complex, [{Fe(CO)3}2{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (5). The ruthenium(II) complex, [{(η6-p-cymene)Ru(μ-Cl)3RuCl}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (6), was obtained on treatment of ligand 1 with [(η6-p-cymene)Ru(Cl)2]2. The reaction between 1 and [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene) in dichloromethane resulted in the formation of a dinuclear complex [{RhCl}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (7), in which the allyl double bond of one of the phenoxy groups coordinates to the metal center. When ligand 1 was reacted with two equivalents of [Pd(COD)Cl2], a dinuclear complex [{PdCl2}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (8) was obtained. With copper(I) halides, ligand 1 afforded tetranuclear complexes, [{(Cu(µ-X)(NCCH3))2}2-

Received 1st September 2013, Accepted 15th October 2013

{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (9, X = Cl; 10, X = Br; 11, X = I). Reaction of 1 with four equivalents of [AuCl(SMe2)] produced a tetranuclear complex, [(AuCl)4{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (12). Complex

DOI: 10.1039/c3dt52400k

8 shows excellent catalytic activity in the Suzuki–Miyaura cross-coupling reaction under microwave con-

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ditions and complex 7 catalyzes hydroformylation of styrenes with good TONs.

Introduction The design and synthesis of polyphosphine ligands has been an active field of research for many years due to the wide structural diversity of their metal complexes.1–3 This class of ligands can readily form multinuclear complexes and also bring two metals into close proximity if the bite distances are short, and in such cases they are useful for the construction of macromolecules, one-, two- or three-dimensional coordination polymers,4–7 as well as conducting polymers if the π-acceptor abilities are comparable with CO.8 Further, the incorporation of donor functionalities (O, N, S, Se or olefins) in close proximity to phosphorus(III) atoms results in functionalized

a Phosphorus Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. E-mail: [email protected], [email protected] b Department of Chemistry, Tulane University, New Orleans, Lousiana 70118, USA † CCDC 955814–955821. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt52400k

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phosphines which are ideally suited for homogeneous catalysis.9–15 Among the known polyphosphines and aminophosphines, those with the PNP backbone are found to be versatile due to their easier synthetic methodology and ability to fine-tune the steric and electronic properties around both phosphorus and nitrogen atoms.16–20 A variety of aminophosphines have been prepared and their metal chemistry and catalytic properties have been explored.20–24 Our research group23 and those of others7,14 have reported many such short-bite, phosphorus-based ligands appended with hetero donor atoms and explored their coordination chemistry and catalytic studies. Herein, we describe the synthesis, coordination behaviour and catalytic activity of bisamino(diphosphonite), p-C6H4{N{P(OC6H4C3H5-o)2}2}2 (1).

Results and discussion The reaction of p-C6H4{N(PCl2)2}2 with an excess of o-allylphenol in the presence of triethylamine afforded phenylene

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{bisamino(diphosphonite)}, p-C6H4{N{P(OC6H4C3H5-o)2}2}2 (1) (referred to as “bis(diphosphonite)” hereafter). Compound 1 is a colourless liquid and is moderately stable to air and moisture. Purification of 1 by distillation was not possible owing to its high boiling point; however, it is pure enough for further reactions according to the 31P{1H} NMR and microanalytical data. The 31P{1H} NMR spectrum of 1 showed a single resonance at 128.2 ppm. In the 1H NMR spectrum, the methylene protons showed a doublet at 3.15 ppm with a 3JHH coupling of 6.4 Hz, while the allylic –CH2 and CH protons showed two multiplets at 4.75–4.82 and 5.66–5.75 ppm, respectively. Bis(diphosphonite) 1 can adopt several conformations depending upon the orientation of the P–N–P backbone with respect to the phenylene ring and also these conformations can lead to the formation of several oligomers or polymers depending upon the coordination geometry of the metals.23a Compound 1 is expected to be a polydentate ligand due to the presence of eight olefinic functionalities in close vicinity to four trivalent phosphorus atoms. Although it can act as a tetradentate ligand, it is anticipated that by choosing appropriate metal precursors and reaction conditions, it would be possible to facilitate the coordination of one or more olefins to the metal centers. In view of this, the coordination chemistry with various transition metals was attempted. The reaction of 1 with two equivalents of [M(CO)4(HNC5H10)2] (M = Mo or W) in dichloromethane at room temperature afforded tetracarbonyl derivatives, cis-[{Mo(CO)4}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (2) and cis-[{W(CO)4}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (3), respectively, as shown in Scheme 1. The 31P{1H} NMR spectra of 2 and 3 showed single resonances at 138.9 and 115.1 ppm, respectively, with the tungsten complex showing a 1JWP coupling of 167.4 Hz. The IR spectra of both complexes 2 and 3 showed four bands in the carbonyl region in the range of 1900–2035 cm−1 as expected for the M(CO)4 moiety of C2v symmetry.2d,25,26 The structures of 2 and 3 were confirmed by single crystal X-ray diffraction studies.

The reaction of 1 with [Fe(η5-C5H5)(CO)2]2 in a 1 : 2 molar ratio in toluene under refluxing conditions for 24 h afforded a green coloured crystalline complex, [{Fe(η5-C5H5)(μ-CO)}4{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (4). Reaction of 1 with Fe(CO)5 in hexane or tetrahydrofuran under photochemical conditions produced [{Fe(CO)3}2{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (5). The 31 1 P{ H} NMR spectra of 4 and 5 displayed single resonances at 172.8 and 141.4 ppm, respectively, with coordination shifts of 44.3 and 13.2 ppm. The IR spectrum of 4 showed a sharp νCO at 1697 cm−1 for the bridging carbonyl groups, whereas complex 5 displayed three strong νCO frequencies in the region 2060–1880 cm−l for terminal carbonyl groups which is in accordance with the literature28 for similar complexes. The reaction of 1 with [Ru(η6-p-cymene)Cl2]2 in a 1 : 2 ratio in THF at 60 °C afforded a tri-chloro bridged tetranuclear complex, [{(η6-p-cymene)Ru(μ-Cl)3RuCl}2{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (6), as an orange crystalline solid (Scheme 1). Elimination of one of the cymene groups from [Ru(η6-p-cymene)Cl2]2 in such reactions is not unusual.23e,f The 31P{1H} NMR spectrum of 6 showed a single resonance at 95.4 ppm. The 1H NMR spectrum of 6 confirms the presence of cymene groups, which showed two doublets centered at 5.48 and 5.32 ppm with a 3JHH coupling of 5.6 Hz. The isopropyl methyl protons appear as a doublet centered at 1.2 ppm with a 3JHH coupling of 6.8 Hz, whereas the chemical shift due to the –CH protons was a multiplet centered at 2.87 ppm. The methyl protons showed a singlet at 2.32 ppm. The reaction of 1 with [Rh(COD)Cl]2 in either 1 : 2 or 1 : 1 molar ratios in dichloromethane afforded [{RhCl}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (7) in 77% yield (Scheme 2). The 31P{1H} NMR spectra of the products obtained from both the reactions showed two doublets of doublets centered at 91.0 (1JRhP = 225.8 Hz) and 87.2 ppm (1JRhP = 238.7 Hz), with a 2JPP coupling of 69.6 Hz which clearly indicated the coordination of one of the olefinic groups to the rhodium atom on each side. Similar but intermolecular olefinic coordination was

Scheme 1


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Scheme 2

observed in copper complexes containing ferrocenylbis( phosphonites) with dangling olefins in para-positions on phosphorus bound aryl moieties.27 The high frequency shift was assigned to the phosphorus atom trans to chlorine. The 1H NMR spectrum of the crude product obtained from the 1 : 2 reaction showed two doublets centered at 1.75 and 3.27 ppm for the methylenic protons, a broad singlet at 4.23 ppm for the olefinic protons of unreacted [Rh(COD)Cl]2, whereas the same proton signals were absent in the complex isolated in 1 : 1 reaction and the purified product in the case of 1 : 2 reaction. The palladium complex [{PdCl2}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (8) was obtained in 79% yield when the ligand 1 was treated with two equivalents of [Pd(COD)Cl2] in dichloromethane at room temperature. The 31P{1H} NMR spectrum of 8 consists of a single resonance at 61.2 ppm. The reaction of 1 with four equivalents of CuX (X = Cl, Br or I) in acetonitrile afforded tetranuclear complexes [{(Cu(µ-X)(NCCH3))2}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (9, X = Cl; 10, X = Br; 11, X = I) in quantitative yield (Scheme 3). All these

complexes are colourless, air-stable crystalline solids and are moderately soluble in common organic solvents. The 31P{1H} NMR spectra of complexes 9–11 showed single resonances at 98.5, 98.2 and 97.0 ppm, respectively. The 1H NMR spectra of all these complexes showed single resonances at 2.15 ppm for the coordinated acetonitrile protons. The analytical data are consistent with the proposed structures and the molecular structures of 9–11 are confirmed by single crystal X-ray diffraction studies. The reaction of 1 with [AuCl(SMe2)] in a 1 : 4 molar ratio afforded a white crystalline complex, [(AuCl)4{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (12). The 31P{1H} NMR spectrum of 12 showed a single resonance at 107.0 ppm. Molecular structures of complexes 2–4 and 9–12 Perspective views of the molecular structures of complexes 2–4 and 9–12 with atom numbering schemes are shown in Fig. 1–7. Selected bond lengths and bond angles are given in Tables 1–4 and crystal data are given in Table 8. The crystal structures of 2 and 3 revealed slightly distorted octahedral

Scheme 3

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Fig. 1 Molecular structure of cis-[{Mo(CO)4}2{p-C6H4{N{P(OC6H4C3H5o)2}2}2}] (2). All hydrogen atoms have been omitted for clarity. Symmetry operation i = 1 − x, 1/2 − y, z. Displacement ellipsoids are drawn at the 50% probability level.

Fig. 2 Molecular structure of cis-[{W(CO)4}2{p-C6H4{N{P(OC6H4C3H5o)2}2}2}] (3). Symmetry operation i = 1 − x, 1/2 − y, z. All hydrogen atoms have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.

geometries around Mo and W, each containing a cis-chelating ligand and four terminal carbon monoxides. The four membered MP2N (M = Mo or W) rings are essentially planar and the P–N–P bond angles are 100.87(16)° (P1–N1–P1a) for 2 and 100.33(13)° (P1–N1–P1a) for 3. The molecular structures of both 2 and 3 possess a crystallographically-imposed mirror symmetry. The two P–N bond distances in 2 and 3 are nearly equal (P1–N1 = 1.699(2) Å for 2 and P1–N1 = 1.6976(17) Å for 3). Slow diffusion of petroleum ether into dichloromethane solution of complex 4 resulted in the formation of two types of crystals (4 and 4a) and for both, the X-ray structures were determined. Complex 4 crystallizes in the triclinic crystal system ˉ as the space group, whereas 4a crystallizes in the with P1


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monoclinic system with P21/c as the space group. The molecular structure of 4 consists of two {cis-Cp2Fe2(μ-CO)2} moieties bridged by ligand 1. The four independent P–N bonds appear as a “short” pair [P1–N1 = 1.692(10) Å and P3–N2 = 1.685(11)] and a “long” pair [P2–N1 = 1.708(10) Å and P4–N2 = 1.716(11)] but in light of the rather large s.u.’s, they all really should be considered equivalent. The Fe–P bond distances in 4 are similar with an average Fe–P distance of 2.111(5) Å. The P–N–P bond angle is 117.6(6)°. The plane of the phenylene spacer is perpendicular to the plane produced by the P–N–P skeleton. The Fe–Fe bond distances are identical [Fe1–Fe2 = Fe3–Fe4 = 2.515(4) Å] and comparable to those found in analogous complexes reported in the literature.28 The two iron atoms and the bridging carbonyl groups are coplanar. The sum of the angles around the nitrogen atoms is 359.8° which indicates the planar geometry around the nitrogen atoms. Compound 4a has the same basic structure as 4 but different orientations of the 2-allylphenyl groups leading to a less compact conformation (Fig. 3). The bond parameters in 4a were found to be similar to those of 4. The molecular structures of 9, 10 and 11 are isotypical (Fig. 4–7) with the primary differences between them being the orientations of the 2-allylphenyl groups. These compounds ˉ with the unit cell of crystallize in the triclinic space group P1 the tetraiodo derivative having a slightly higher cell volume (ca. 9.7% more than that for 9 and 10) due to the bulkier iodine atoms. The molecular structures of 9, 10 and 11 consist of discrete Cu2X2 cores having a crystallographically-imposed centrosymmetry. In their crystal structures, all the copper(I) centres are tetrahedrally coordinated to one phosphorus atom, two bridging halides and one acetonitrile molecule. The Cu2X2 core adopts a butterfly shape with the halide atoms at the wingtips. The four Cu–X bond distances differ significantly from one another but roughly fall into a longer pair and a shorter pair (i.e. each copper atom has one long Cu–X bond and one short one). The distances between the two copper centers in 9, 10 and 11 are 2.6893(4), 2.7177(8) and 2.6906(8) Å, respectively, which indicates the presence of ligand-supported Cu⋯Cu interactions.23b In the molecular structure of 10 and 11, the two independent Cu–P distances differ slightly (Cu1–P1 = 2.1804(11) Å and Cu2–P2 = 2.1763(11) Å) for 10, and (Cu1–P1 = 2.1988(9) Å and Cu2–P2 = 2.2032(9) Å) for 11, while in 9, the two independent Cu–P distances are nearly the same (Cu1–P1 = 2.1748(5) Å and Cu2–P2 = 2.1740(5) Å). The X–Cu–X angles Cl1–Cu1–Cl2 = 100.55(3)° and Cl1–Cu2–Cl2 = 100.07(2)° for 9, Br1–Cu1–Br2 = 97.38(2)° and Br1–Cu2–Br2 = 97.95(2)° for 10 and I1–Cu1–I2 = 104.45(1)° and I1–Cu2–I2 = 104.37(2)° for 11 indicate the distorted tetrahedral environment around the copper centers. The angles around the halide atoms Cu1–Cl1–Cu2 = 66.70(2)° and Cu1–Cl2–Cu2 = 69.31(2)° for 9, Br1–Br1–Cu2 = 66.70(2)° and Br1–Br2–Cu2 = 69.31(2)° for 10 and Cu1–I1–Cu2 = 59.77(1)° and Cu1–I2–Cu2 = 61.34(1)° for 11 are quite small. The torsion angles observed between the phenylene spacer and the P–N–P plane are P1–N1 vs. C37– C39a = 96.17(19)° for 9, P1–N1 vs. C37–C38 = 92.80(4)° for 10 and P1–N1 vs. C37–C38 = 89.7(3)° for 11.

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Fig. 3 Molecular structure of [{Fe(η5-C5H5)(μ-CO)}4{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (4 & 4a). Symmetry operation i = −x, 1 − y, −z for 4 and symmetry operation i = 1 + x, y, z for 4a. All hydrogen atoms have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.

Fig. 4 Molecular structure of [{(Cu(µ-Cl)(NCCH3))2}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (9). Symmetry operation i = 2 − x, 1 − y, −z. All hydrogen atoms have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.

The molecular structure of 12 reveals the presence of a crystallographically-imposed two-fold rotation symmetry. The AuI centers adopt an approximately linear geometry with P–Au–Cl angles of 172.84(3)° and 174.05(3)°. The P–Au–Cl units are cis-oriented with the intramolecular Au⋯Au distance of 3.214 Å, which is well within the distance considered to represent an aurophilic interaction.29 The independent Au–P distances (Au1–P1 = 2.1979(6) Å and Au2–P2 = 2.1992(6) Å) and Au–Cl distances (Au1–Cl1 = 2.2674(6) Å and Au2–Cl2 = 2.2714(6) Å) are comparable though slightly different. The P1–N–P2 bond angle is 118.27(11)°. The torsion angles observed between the bridging phenylene ring and the P–N–P plane (P1–N1 vs. C37–C38) is 62.04°.

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Fig. 5 Molecular structure of [{(Cu(µ-Br)(NCCH3))2}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (10). Symmetry operation i = 1 − x, 1 − y, 2 − z. All hydrogen atoms have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.

Hydroformylation reactions The industrially important homogeneous catalytic process, hydroformylation, still needs expansion of its ligand library. While metal complexes of many short-bite bidentate ligands have shown very poor activity, some exceptional complexes coordinated to short-bite ligands such as bis(diphenylphosphino)methane (dppm) have shown better results.30 Complexes of several tetradentate phosphorus-based ligands have also been tested for hydroformylation and have shown good catalytic activity with excellent selectivity.31 The dinuclear rhodium complex 7 with short-bite angles was employed in the hydroformylation of styrenes. The results are summarized in Table 5. The conversion of styrene increases with pressure (entries 1–3). Hence the optimized conditions include 60 °C, 30 bar pressure with an S/C ratio of 10 000. A good selectivity


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of approximately 80% was achieved for styrene at 30 bar pressure and 60 °C but at 85 °C the performance was even better. Using these optimized conditions, the substrate scope has been explored with various styrene derivatives having different substituents. Satisfactory TONs of 9000 were achieved using complex 7. Earlier attempts to employ this type of bisphosphonite complexes in hydroformylation reactions have been unsuccessful.32 To the best of our knowledge, this is the first report where an amine-based bis(diphosphonite) complex has been employed in hydroformylation reactions with good catalytic efficiency. Suzuki–Miyaura reaction

Fig. 6 Molecular structure of [{(Cu(µ-I)(NCCH3))2}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (11). Symmetry operation i = −x, −y, −z. All hydrogen atoms have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.

Fig. 7 Molecular structure of [(AuCl)4{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (12). Symmetry operation i = 2 − x, 1 − y, 1 − z. All hydrogen atoms have been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.

Table 1

One of the simplest and best ways of aryl–aryl bond formation is the Suzuki–Miyaura cross-coupling reaction which uses aryl boronic acids (less toxic and thus easy to handle) and has found vast applications in fine chemical syntheses used in optical materials and medicine. Excellent catalytic activity observed with complexes containing bisphosphonite ligands23d,33 prompted us to investigate the catalytic potential of the dipalladium(II) complex 8. In recent years, microwave irradiation has become a very popular method since it presents a faster, cleaner and high-yielding technology for catalysis.34 This is the first report where a dipalladium(II) complex containing a bis(diphosphonite) ligand is employed in the Suzuki–Miyaura cross-coupling reaction under microwave irradiation. Among the various solvents and bases tested, the best results were obtained from methanol and K2CO3. With a catalyst load of 0.05 mol%, 1.2 equivalents of boronic acid and 1.5 equivalents of base in 5 min under microwave irradiation of 60 W, an excellent TOF of 22 800 was achieved with bromotoluene (Table 6, entry 1). Even for electron-donating groups such as methyl, methoxy and NMe2 which are deactivating, very good TOFs were observed (entries 2–8). Aryl halides having ortho substituents are sterically hindered and as a result are poor substrates for cross-coupling reactions. However, complex 8 was able to catalyze the coupling of these aryl bromides with phenylboronic acid which resulted in enhanced TOFs (entries 5–7 & 12–14) of 24 000 for acyl and formyl substituents. Heteroaromatic bromides which require

Selected bond distances and bond angles of complexes 2 and 3

Compound 2

Compound 3

Bond length (Å) Mo1–P1 Mo1–P1a P1–N1 Mo1–C21 Mo1–C22 Mo1–C21a Mo1–C22a P1–O1 P1–O2 O3–C21 O4–C22

Bond angle (°) 2.4422(8) 2.4422(8) 1.699(2) 2.052(3) 2.018(3) 2.052(3) 2.018(3) 1.617(2) 1.614(2) 1.138(4) 1.142(4)

P1–N1–P1a P1–Mo1–P1a P1–Mo1–C21 P1–Mo1–C22 P1–Mo1–C21a P1–Mo1–C22a P1a–Mo1–C21 P1a–Mo1–C22 P1a–Mo1–C21a P1a–Mo1–C22a Mo1–P1–N1


Bond length (Å) 100.87(16) 64.86(3) 93.07(9) 164.96(9) 95.61(9) 100.29(9) 95.61(9 100.29(9) 93.07(9) 164.96(9) 97.14(9)

W1–P1 W1–P1a P1–N1 W1–C21 W1–C22 W1–C21a W1–C22a P1–O1 P1–O2 O3–C21 O4–C22

Bond angle (°) 2.4352(6) 2.4352(6) 1.6976(17) 2.044(3) 2.016(3) 2.044(3) 2.016(3) 1.6160(18) 1.6131(18) 1.138(4) 2.4352(6)

P1–N1–P1a P1–W1–P1a P1–W1–C21 P1–W1–C22 P1–W1–C21a P1–W1–C22a P1a–W1–C21 P1a–W1–C22 P1a–W1–C21a P1a–W1–C22a

100.33(13) 64.73(2) 93.21(8) 164.50(8) 95.94(8) 100.00(8) 95.94(8) 100.00(8) 93.21(8) 164.50(8)

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Dalton Transactions Selected bond distances and bond angles of complexes 4 and 4a

Compound 4

Compound 4a


Bond length (Å) Fe1–Fe2 Fe1–P1 Fe2–P2 P1–N1 P2–N1 P3–N2 P4–N2 Fe3–P3 Fe4–P4 Fe3–Fe4

Table 3 X = I)

Bond angle (°) 2.515(4) 2.115(5) 2.110(5) 1.692(12) 1.710(12) 1.684(13) 1.716(12) 2.110(5) 2.109(5) 2.515(3)

P1–N1–P2 P3–N2–P4 Fe2–Fe1–P1 Fe1–Fe2–P2 Fe4–Fe3–P3 Fe3–Fe4–P4 Fe1–P1–N1 Fe2–P2–N1 Fe3–P3–N2 Fe4–P4–N2

Bond length (Å) 117.6(6) 118.2(6) 95.12(14) 94.60(14) 95.27(15) 94.87(14) 115.3(4) 115.1(4) 115.23(4) 114.7(4)

Fe1–Fe2 Fe1–P1 Fe2–P2 P1–N1 P2–N1 P3–N2 P4 –N2 Fe3–P3 Fe4–P4 Fe3–Fe4

Bond angle (°) 2.5182(10) 2.1192(13) 2.1097(13) 1.700(3) 1.701(3) 1.697(3) 1.698(3) 2.1147(13) 2.1178(13) 2.5221(10)

P1–N1–P2 P3–N2–P4 Fe2–Fe1–P1 Fe1–Fe2–P2 Fe4–Fe3–P3 Fe3–Fe4–P4 Fe1–P1–N1 Fe2–P2–N1 Fe3–P3–N2 Fe4–P4–N2

117.9(2) 118.5(2) 95.18(4) 94.76(4) 95.02(4) 94.72(4) 114.98(12) 115.43(12) 114.93(4) 114.62(12)

Selected bond distances and bond angles of complexes, [{(Cu(µ-X)(NCCH3))2}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (9, X = Cl; 10, X = Br; 11,

Bond length (Å)

Bond angle (°)

Compound

9

10

11

Compound

9

10

11

P1–N1 P2–N1 P1–O1 P1–O2 P2–O3 P2–O4 Cu1–X1 Cu1–X2 Cu2–X1 Cu2–X2 Cu1–P1 Cu2–P2 Cu1–N2 Cu2–N3 Cu1–Cu2

1.6938(15) 1.6919(15) 1.6227(15) 1.6277(15) 1.6243(15) 1.6300(15) 2.4451(7) 2.3763(7) 2.4469(7) 2.3530(8) 2.1748(5) 2.1740(5) 1.971(2) 1.9704(19) 2.6983(4)

1.691(3) 1.696(3) 1.626(3) 1.631(3) 1.622(3) 1.625(3) 2.4620(7) 2.5659(7) 2.5077(7) 2.5383(7) 2.1804(11) 2.1763(11) 1.974(3) 1.966(9) 2.7177(8)

1.694(3) 1.701(3) 1.630(2) 1.625(2) 1.632(2) 1.630(2) 2.6739(7) 2.7257(7) 2.6620(7) 2.6123(7) 2.1988(9) 2.2032(9) 1.984(3) 1.986(3) 2.6906(8)

P1–N1–P2 X1–Cu1–X2 X1–Cu2–X2 Cu1–X1–Cu2 Cu1–X2–Cu2 X1–Cu1–P1 X2–Cu1–P1 X1–Cu2–P2 X2–Cu2–P2 X1–Cu1–N2 X1–Cu2–N3 X2–Cu1–N2 X2–Cu2–N3 P1–Cu1–N2 P2–Cu2–N3

117.58(8) 97.38(2) 97.95(2) 66.70(2) 69.31(2) 106.25(2) 116.98(2) 107.49(2) 116.63(2) 108.95(6) 103.83(6) 100.43(6) 107.18(6) 123.70(6) 120.55(6)

118.31(17) 100.55(3) 100.07(2) 66.30(2) 64.34(2) 114.76(3) 108.23(3) 115.86(3) 107.47(3) 107.28(10) 97.6(11) 102.15(10) 110.8(10) 121.17(10) 122.6(11)

117.93(14) 104.45(1) 104.37(2) 59.77(1) 61.34(1) 107.12(3) 117.47(3) 110.79(3) 111.75(3) 110.36(9) 100.68(9) 105.61(9) 106.07(9) 116.11(9) 117.29(9)

Table 4 Selected bond distances and bond angles of complex 12

[(AuCl)4{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (12) Bond length (Å) P1–N1 P2–N1 P1–O1 P1–O2 P2–O3 P2–O4 Au1–P1 Au2–P2 Au1–Cl1 Au2–Cl2

Bond angle (°) 1.688(2) 1.685(2) 1.5874(19) 1.5871(18) 1.5992(18) 1.5961(18) 2.1979(6) 2.1992(6) 2.2673(6) 2.2714(8)

P1–N1–P2 Au1–P1–N1 Au2–P2–N1 Au1–P1–O1 Au1–P1–O2 Au2–P2–O3 Au2–P2–O4 Cl1–Au1–P1 Cl2–Au2–P2

118.27(11) 113.62(7) 116.36(7) 116.19(7) 118.68(7) 117.41(7) 114.29(7) 172.84(3) 174.05(3)

expected, complex 8 could catalyze methyl and methoxy substituted boronic acids efficiently (Table 7, entries 21–23). With electron withdrawing substituents, which deactivate the phenyl boronic acid, complex 8 performed reasonably well (entries 24–30) with a TOF of 23 520 for 4-fluorobenzene boronic acid. These results clearly indicate that complex 8 is a highly promising and successful catalyst for Suzuki–Miyaura cross-coupling reactions and the possibility for extension to other coupling reactions. However, the catalytic efficiency of complex 8 towards aryl chlorides was not satisfactory.

Conclusions harsh conditions for coupling reactions were also coupled efficiently with phenyl boronic acid with TOFs of 18 000–24 000 (entries 16–19). In order to establish the efficiency and versatility of the precatalyst 8, different aryl boronic acids have been tested and the results are summarized in Table 6. It is well known that boronic acids with electron donating substituents are more nucleophilic than electron withdrawing ones and perform better in the coupling reaction as compared to the latter. As

1088 | Dalton Trans., 2014, 43, 1082–1095

The short bite bis(diphosphonite) ligand 1 exhibits both chelating as well as bridging bidentate modes of coordination. Ligand 1 on treatment with molybdenum and tungsten carbonyl derivatives afforded bis-chelated complexes, whereas with [Fe(η5-C5H5)(CO)2]2 yielded the tetranuclear complex, [{Fe(η5C5H5)(μ-CO)}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (4), which crystallized in two different crystal systems with different unit cell parameters. Reaction of 1 with Fe(CO)5 afforded a chelate complex, [{Fe(CO)3}2{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (5). The


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Dalton Transactions Table 5


Entry 1 2 3 4 5 6 7 8

Paper

Hydroformylation of styrenes using complex 7

Substrate Styrene Styrene Styrene Styrene 4-Me styrene 4-tBu styrene 4-Cl-styrene 4-Br-styrene

P (Bar) 20 30 40 30 30 30 30 30

Time (h) 2 2 2 4 4 4 4 4

Conversion (%) a

61 73a 76a 100b 97b 94b 89b 88b

Branched : linear

TON

57 : 43 78 : 22 47 : 53 62 : 38 69 : 31 48 : 52 61 : 39 50 : 50

6100 7300 7600 10 000 9700 9400 8900 8800

Substrate/catalyst ratio: 10 000; temperature: a 60 °C. b 85 °C.

reaction of 1 with [(η6-cymene)Ru(Cl)2]2 yields a trichlorobridged complex. The coordination of one of the dangling olefins was observed only in the case of the rhodium complex. With copper(I) halides, tetranuclear complexes were isolated in which the Cu2X2 core adopts a butterfly shape with the halide atoms at the wingtips. The tetranuclear gold(I) complex 12 showed a short Au⋯Au contact of 3.214 Å. Complex 7 is moderately active in catalyzing hydroformylation of styrenes and the palladium complex 8 is found to be an efficient catalyst under microwave irradiation for Suzuki–Miyaura coupling reaction with excellent TOFs for a variety of aryl bromides and aryl boronic acid derivatives.

Experimental section Reagents and methods All experimental manipulations were performed under an inert atmosphere of dry nitrogen or argon using standard Schlenk techniques. All the solvents were purified by conventional procedures and distilled prior to use. M(CO)4(HNC5H10) (M = Mo or W),35 [Ru-(η6-p-cymene)Cl2],36 [Rh(COD)Cl]2,37 CuCl, CuBr38 and [AuCl(SMe2)]39 were prepared according to the published procedures. Copper(I) iodide, Fe(CO)5 and [Fe(Cp)(CO)2]2 were purchased from Aldrich Chemicals and used as received. Other reagents were obtained from commercial sources and used after purification. The 1H and 31P{1H} NMR (δ in ppm) spectra were obtained using a Varian VRX 400 spectrometer operating at frequencies of 400 and 162 MHz, respectively. The spectra were recorded in CDCl3 (or DMSO-d6) solutions with CDCl3 (or DMSO-d6) as an internal lock; TMS and 85% H3PO4 were used as internal and external standards for 1H and 31P{1H}NMR, respectively. Positive values indicate downfield shifts. Microanalyses were carried out using a Carlo Erba (model 1106) elemental analyzer. Melting points of all compounds were determined using a Veego melting point apparatus and are uncorrected. Hydroformylation reactions were performed in a custom made high pressure autoclave of 100 mL capacity manufactured by M/s Amar Equipments


Private Ltd, Mumbai, India. Microwave experiments were carried out using a CEM Discover Labmate microwave apparatus. GC analyses were conducted using an Agilent Gas Chromatograph 6890 Series, Hewlett Packard, equipped with an HP5-MS capillary column (30 m × 0.25 mm × 0.25 μm) and an FID detector. Synthesis of p-C6H4{N{P(OC6H4C3H5-o)2}2}2 (1). To the solution of p-C6H4{N(PCl2)2}2 (1.1275 g, 2.0 mmol) in 20 mL of diethyl ether was added a mixture of o-allyl phenol (2.39 g, 17.8 mmol) and triethylamine (1.87 g, 17.8 mmol) also in 15 mL diethyl ether dropwise at 0 °C. The reaction mixture was warmed to room temperature and stirred overnight. The triethylamine hydrochloride formed was filtered through a frit containing a celite bed. All the solvent was evaporated under vacuum and the resulting mixture was washed several times with petroleum ether and dried to get a colourless oily product. Yield: 85% (2.418 g). Anal. calcd for C78H76N2O8P4: C, 72.42; H, 5.93; N, 2.17%. Found: C, 71.87; H, 5.85; N, 2.05%. MS (EI): m/z = 1293.45 (M + 1). 31P{1H} NMR (CDCl3) δ: 126.4 (s). 1H NMR (CDCl3) δ: 3.15 (d, CH2, 16H, 3JHH = 6.4 Hz), 5.056 (m, CH2, 16H), 5.88–5.96 (m, CH, 8H), 6.6–7.57 (m, ArH, 36H). MS (EI): m/z = 1293.45 (M + 1). Synthesis of cis-[{Mo(CO)4}2{p-C6H4{N{P(OC6H4C3H5o)2}2}2}] (2). A solution of [Mo(CO)4(HNC5H10)2] (0.020 g, 0.0538 mmol) in dichloromethane (5 mL) was added dropwise to the solution of 1 (0.035 g, 0.0269 mmol) in dichloromethane (5 mL) and the reaction mixture was stirred at room temperature for 12 h. All the solvent was evaporated to get a pale yellow colour solid product. It was washed with petroleum ether (7 mL) and dried under vacuum to get an analytically pure product of 2 as a pale yellow colour solid. Yield: 43% (0.019 g). MP: 198–200 °C. Anal. calcd for C86H76N2O16P4Mo2: C, 60.43; H, 4.48; N, 1.64%. Found: C, 60.35; H, 4.33; N, 1.68%. 31P{1H} NMR (CDCl3) δ: 138.9 (s). 1H NMR (CDCl3) δ: 3.21 (d, CH2, 16H, 3JHH = 6.4 Hz), 4.73–4.85 (m, CH2, 16H), 5.64–5.73 (m, CH, 8H), 7.04–7.96 (m, ArH, 36H). IR (νCO) (KBr disk): 1920, 1948 (br), 1983, 2038 cm−1. Synthesis of cis-[{W(CO)4}2{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (3). It was prepared analogous to 2 using [W(CO)4(HNC5H10)2]

Dalton Trans., 2014, 43, 1082–1095 | 1089

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Dalton Transactions

Table 6 Suzuki–Miyaura reaction of phenylboronic acid with various aryl bromidesa


b

Entry

Aryl halide

Product

Conv. (%)

TOF (h−1)

1

95

22 800

2

92

22 080

3

96

23 040

4

97

23 280

5

82

19 680

6

65

15 600

7

96

23 040

8

99

23 760

9

97

23 280

10

100

24 000

11

99

23 760

12

100

24 000

13

14

100

92

Table 6

(Contd.)

Entry

Aryl halide

Conv.b (%)

TOF (h−1)

18

100

24 000

19

23

5520

20

100

24 000

a Reaction performed in a sealed tube, using 0.242 mmol aryl bromides, 0.29 mmol (1.2 eq.) aryl boronic acid, 0.363 mmol (1.5 eq.) base with 0.05 mol% Pd complex in 3 mL solvent. An initial microwave power of 60 W is applied to reach 85 °C temperature. b Conversion based on aryl bromides determined by GC using dodecane as an internal standard.

Table 7 Suzuki–Miyaura reaction of 4-bromotoluene with various arylboronic acid derivativesa

Entry Aryl boronic acid

Product

Conv.b TOF (%) (h−1)

21

99

23 760

22

98

23 520

23

96

23 040

24

92

22 080

25

98

23 520

26

89

21 360

27

91

21 840

28

86

20 640

29

98

23 520

30

84

20 160

24 000

22 080

15

100

24 000

16

75

18 000

17

100

24 000

a and b

1090 | Dalton Trans., 2014, 43, 1082–1095

Product

are described in Table 6.


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Dalton Transactions

(0.022 g, 0.047 mmol) and ligand 1 (0.030 g, 0.0235 mmol). Yield: 42% (0.018 g). MP: >185 °C (decomp.). Anal. calcd for C86H76N2O16P4W2: C, 54.79; H, 4.06; N, 1.48%. Found: C, 54.63; H, 4.38; N, 1.66%. 31P{1H} NMR (CDCl3) δ: 115.1 (s, 1JWP = 167.4 Hz). 1H NMR (CDCl3) δ: 3.21 (d, CH2, 16H, 3JHH = 6.4 Hz), 4.73–4.85 (m, CH2, 16H), 5.64–5.73 (m, CH, 8H), 7.04–7.96 (m, ArH, 36H). IR (νCO) (KBr disk): 1939 (br), 1974, 2035 cm−1. Synthesis of [{Fe(η5-C5H5)(μ-CO)}4{p-C6H4{N{P(OC6H4C3H5o)2}2}2}] (4). A mixture of ligand 1 (0.075 g, 0.0583 mmol) and [Fe(η5-C5H5)(CO)2]2 (0.041 g, 0.1166 mmol) in toluene (15 mL) was refluxed for 24 h to get a dark green colour solution. The solution was dried under vacuum to get a pasty residue which was washed with petroleum ether and dried under reduced pressure to get an analytically pure product of 4 as a dark green crystalline solid. Yield: 88% (0.097 g). MP: >200 °C (decomp.). Anal. calcd for C102H96Fe4N2O12P4: C, 64.85; H, 5.12; N, 1.48%. Found: C, 64.65; H, 5.33; N, 1.78%. 31P{1H} NMR (CDCl3) δ: 172.8 (s). 1H NMR (CDCl3) δ: 3.04–3.15 (m, CH2, 16H), 4.19 (s, C5H5, 20H), 4.81–4.98 (m, CH2, 16H), 5.71–5.81 (m, CH, 8H), 6.86–7.52 (m, ArH, 36H). IR (νCO) (KBr disk): 1697 cm−1. Synthesis of [{Fe(CO)3}2{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (5). A mixture of 1 (0.104 g, 0.0804 mmol) and Fe(CO)5 (0.031 g, 0.1608 mmol) in petroleum ether (20 mL) was exposed to UV light (150 W) for 6 h with constant stirring during which time the yellow coloured solution turned slightly brown. The reaction mixture was filtered through a frit and the solution was concentrated under vacuum to get an analytically pure product of 5 as a yellowish brown solid. Yield: 87% (0.108 g). MP: 98–100 °C. Anal. calcd for C84H76N2O14P4Fe2: C, 64.13; H, 4.87; N, 1.78%. Found: C, 64.25; H, 4.63; N, 1.54%. 31 1 P{ H} NMR (CDCl3) δ: 141.4 (s). IR (νCO) (KBr disk): 1940, 1989, 2020 cm−1. Synthesis of [{(η6-p-cymene)Ru(μ-Cl)3RuCl}2{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (6). A mixture of 1 (0.048 g, 0.0375 mmol) and [Ru(η6-p-cymene)(Cl)2]2 (0.046 g, 0.075 mmol) in THF (15 mL) was refluxed at 60 °C for 6 h. The reddish colored reaction mixture obtained was cooled to room temperature and the solvent was removed under vacuum to get a yellow coloured solid product. The residue was dissolved in dichloromethane and layered with petroleum ether and stored at room temperature to give X-ray quality product of 6 as red crystals. Yield: 77% (0.065 g). MP: >170 °C (decomp.). Anal. calcd for C98H104N2O8P4Ru4Cl8: C, 52.32; H, 4.66; N, 1.24%. Found: C, 52.62; H, 4.56; N, 1.34%. 31P{1H} NMR (CDCl3) δ: 95.4 (s). 1H NMR (CDCl3) δ: 1.24 (d, CH3, 12H, 3JHH = 6.7 Hz), 2.32 (s, CH3, 6H), 2.8 (sept, CH, 2H), 3.26 (br s, CH2, 16H), 4.74–4.99 (m, CH2, 16H), 5.72–5.81 (m, CH, 8H), 5.31, 5.48 (2d, C6H4, 8H, 3JHH = 5.6 Hz), 6.87–7.17 (m, ArH, 36H). Synthesis of [{RhCl}2{p-C6H4{N(P(OC6H4C3H5-o)2)2}2}] (7). A dichloromethane (5 mL) solution of [Rh(COD)Cl]2 (0.015 g, 0.031 mmol) was added to the solution of ligand 1 (0.04 g, 0.031 mmol) also in dichloromethane (5 mL) at room temperature with constant stirring. The reaction mixture was stirred for 4 h and the solvent was concentrated under vacuum to 2 mL, petroleum ether (3 mL) was added to get an analytically


Paper

pure product of 7 as a yellowish-orange solid. Yield: 79% (0.038 g). MP: >180 °C (decomp.). Anal. calcd for C78H76N2P4Rh2Cl2O8.CH2Cl2: C, 55.22; H, 4.63; N, 1.61%. Found: C, 55.45; H, 4.68; N, 1.89%. 31P{1H} NMR (CDCl3) δ: 91.0 (dd, 1JRhP = 225.8 Hz, 2JPP = 69.6 Hz), 87.2 (dd, 1JRhP = 238.7 Hz, 2JPP = 69.6 Hz). 1H NMR (CDCl3) δ: 3.22–3.39 (br m, CH2, 8H) 4.02 (d, CH2, trans-H, 2H, 3JHH = 15.99 Hz), 4.49 (d, CH2, cis-H, 2H, 3JHH = 7.99 Hz), 4.89 (d, CH2, trans-H, 2H, 3 JHH = 15.99 Hz), 4.95 (d, CH2, cis-H, 2H, 3JHH = 7.99 Hz), 5.71–5.86 (m, CH, 8H), 7.01–7.81 (m, ArH, 21H). Synthesis of [{PdCl2}2{C6H5N{P(OC6H4C3H5-o)2}2}] (8). A solution of Pd(COD)Cl2 (0.024 g, 0.086 mmol) in dichloromethane (5 mL) was added dropwise to the solution of 1 (0.059 g, 0.086 mmol) also in dichloromethane (5 mL) and the reaction mixture was stirred at room temperature for 4 h. The solvent was evaporated under reduced pressure to get a pale yellow colored oily product. It was washed with petroleum ether (7 mL) and dried under vacuum to get analytically pure product of 8 as a pale yellow solid. Yield: 79% (0.059 g). MP: 110–111 °C. Anal. calcd for C42H41NO4P2PdCl2: C, 58.75; H, 5.16; N, 1.59%. Found: C, 59.15; H, 4.93; N, 1.78%. 31P{1H} NMR (CDCl3) δ: 61.2 (s). 1H NMR (CDCl3) δ: 3.26 (d, CH2, 8H, 3 JHH = 4 Hz), 4.83–4.91 (m, CH2, 8H), 5.69–5.77 (m, CH, 4H), 6.60–7.57 (m, ArH, 21H). MS (EI): m/z = 1533.20 (M − Cl)+. Synthesis of [{Cu(µ-Cl)(NCCH3)}4{p-C6H4{N{P(OC6H4C3H5o)2}2}2}] (9). To a solution of cuprous chloride (0.014 g, 0.15 mmol) in acetonitrile (5 mL) was added dropwise a solution of 1 (0.047 g, 0. 0366 mmol) in acetonitrile (5 mL) and the reaction mixture was stirred at room temperature for 4 h. The solvent was evaporated under reduced pressure to get a colourless oily product. It was washed with petroleum ether (7 mL) and dried under vacuum to get a white solid. The product was recrystallized from a mixture of dichloromethane and petroleum ether by slow evaporation to get X-ray quality crystals of 9 as a colourless crystalline solid. Yield: 89% (0.0604 g). MP: >230 °C. Anal. calcd for C86H88Cl4Cu4N6O8P4: C, 55.72; H, 4.78; N, 4.53%. Found: C, 55.68; H, 4.63; N, 4.78%. 31P{1H} NMR (DMSO-d6) δ: 98.5 (br s). 1H NMR (DMSO-d6) δ: 2.43 (s, CH3, 12H), 2.87 (br s, CH2, 16H), 4.69–4.8 (m, CH2, 16H), 5.57 (m, CH, 8H), 7.07–7.65 (m, ArH, 36H). Synthesis of [{Cu(µ-Br)(NCCH3)}4{p-C6H4{N{P(OC6H4C3H5o)2}2}2}] (10). Compound 10 was synthesized by a procedure similar to that of 9 using cuprous bromide (0.023 g, 0.1636 mmol) and 1 (0.053 g, 0.0409 mmol). Yield: 91% (0.0714 g). MP: >230 °C. Anal. calcd for C86H88Br4Cu4N6O8P4: C, 50.84; H, 4.36; N, 4.14%. Found: C, 50.45; H, 4.13; N, 4.32%. 31P{1H} NMR (DMSO-d6) δ: 98.2 (br s). 1H NMR (DMSOd6) δ: 2.58 (s, CH3, 12H), 2.98 (d, CH2, 16H, 3JHH = 6.4 Hz), 4.57–4.66 (m, CH2, 16H), 5.51–5.55 (m, CH, 8H), 7.09–7.72 (m, ArH, 36H). Synthesis of [{Cu(µ-I)(NCCH3)}4{p-C6H4{N{P(OC6H4C3H5o)2}2}2}] (11). Compound 11 was synthesized by a procedure similar to that of 9 using cuprous iodide (0.031 g, 0.1636 mmol) and ligand 1 (0.053 g, 0.0409 mmol). Yield: 93% (0.084 g). MP: >230 °C. Anal. calcd for C86H88I4Cu4N6O8P4: C, 46.54; H, 3.99; N, 3.78%. Found: C, 46.34; H, 3.74; N, 3.70%.

Dalton Trans., 2014, 43, 1082–1095 | 1091

1092 | Dalton Trans., 2014, 43, 1082–1095

a

C78H76Au4Cl4N2O8P4

12

R1 = ∑||Fo| − |Fc|/∑|Fo|; wR2 = {[∑w(|Fo|2|Fc|2)2]/[∑w(|Fo|2)2]}1/2.

4178 [Rint = 0.0696] 0.1177 0.1936 0.936

1960 100 1.0, 25.0 15 591 11 945 [Rint = 0.0937] 0.0650 0.1362 1.020

3928 100 1.21, 27.5 20 295

15 088 [Rint = 0.0355] 0.0417 0.1001 1.019

954 100 2.1, 28.5 19 122

6342 [Rint = 0.0435] 0.0420 0.1002 1.056

1026 100 1.33, 25.75 8129

10 156 [Rint = 0.0356] 0.0364 0.0987 1.054

1142 100 2.09, 28.12 11 466

9896 [Rint = 0.041] 0.0187 0.0393 1.04

4445 [Rint = 0.0435] 0.0270 0.0595 1.029

11

9334 [Rint = 0.0622] 0.0476 0.1101 1.712

10

2132 100 2.0, 28.5 68 946

9

3768 100 2.5, 29.2 5271

4a

3528 100 1.5, 27.9 12 904

4

2222.95 Monoclinic P21/c 14.1051(8) 15.3140(8) 18.5847(10) 90 102.948(1) 90 3912.3(4) 2 1.887 7.750

3

C43H40NO8P2Mo C43H38NO8P2W C102H94Fe4N2O12P4 C102H96Fe4N2O12P4 C86H88Cl4Cu4N6O8P4 C86H88Br4Cu4N6O8P4 C86H88Cu4I4N6O8P4.2 (C2H3N) 856.64 945.54 1887.07 1889.09 1853.46 2031.30 2301.37 Tetragonal Tetragonal Triclinic Monoclinic Triclinic Triclinic Triclinic ˉ ˉ ˉ ˉ I41/a P1 P21/c P1 P1 P1 I41/a 21.060(2) 21.0377(17) 15.222(5) 15.694(4) 10.1635(8) 10.2115(19) 10.583(2) 21.060(2) 21.0377(17) 15.757(6) 24.793(6) 14.0031(10) 13.988(3) 14.336(3) 17.7326(19) 17.7433(15) 20.793(8) 24.102(6) 16.8906(13) 16.974(4) 17.250(3) 90 90 93.652(6) 90.0 69.067(1) 68.746(3) 100.788(2) 90 90 98.092(6) 108.831(3) 73.043(1) 73.126(2) 104.252(2) 90 90 115.125(5) 90.0 82.968(1) 82.826(2) 104.309(2) 7864.8(14) 7852.9(11) 4428(3) 8876(4) 2147.2(3) 2161.8(7) 2370.7(8) 8 8 2 4 1 1 1 1.447 1.594 1.415 1.414 1.433 1.560 1.612 0.470 3.078 0.780 0.778 1.234 2.950 2.311

2

Crystallographic information for compounds 2–4 and 9–12a

FW Crystal system Space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z ρcalc. (g cm−3) µ (MoKα), (mm−1) F(000) T (K) θ Range (°) Total no. of reflns No. of indep. reflns R1 wR2 S

Formula

Table 8


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Dalton Transactions

P{1H} NMR (DMSO-d6) δ: 97.1 (br s). 1H NMR (DMSO-d6) δ: 2.53 (s, CH3, 12H), 2.91 (br s, CH2, 16H), 4.52–4.61 (m, CH2, 16H), 5.43–5.52 (m, CH, 8H), 7.04–7.65 (m, C6H5, 36H). Synthesis of [(AuCl)4{p-C6H4{N{P(OC6H4C3H5-o)2}2}2}] (12). A solution of [AuCl(SMe2)] (0.078 g, 0.264 mmol) in dichloromethane (5 mL) was added dropwise to the solution of 1 (0.046 g, 0.066 mmol) also in dichloromethane (5 mL) at room temperature with constant stirring. The reaction mixture was stirred for 4 h. The solvent was removed under reduced pressure to get a colourless oily product. The oily product was dissolved in dichloromethane, layered with petroleum ether and kept for slow evaporation to get colourless crystals of 12. Yield: 76% (0.11 g). MP: 169–172 °C. Anal. calcd for C78H76Au4Cl4N2O8P4: C, 42.14; H, 3.45; N, 1.26%. Found: C, 42.46; H, 3.21; N, 1.53%. 31P{1H} NMR (DMSO-d6) δ: 107.0 ppm (s). 1H NMR (DMSO-d6) δ: 3.16 (br s, CH2, 16H), 4.77 (d, trans-H, 8H, 3JHH = 16.8 Hz), 4.95 (d, cis-H, 8H, 3JHH = 10.4 Hz), 5.64–5.70 (m, CH, 8H), 7.21–7.74 (m, ArH, 36H).


31

General procedure for hydroformylation reactions In a typical hydroformylation reaction, to a high pressure reactor of 60 mL capacity, 0.002 g (1.27 × 10−6 mmol) of complex 8, 1.326 g (1.27 mmol) of styrene and 20 mL of toluene were added. The reactor was flushed with synthesis gas (1 : 1 mixture of H2 and CO gas) followed by charging to the desired pressure at room temperature. The reactor was heated to the desired temperature with a stirring speed of 350 rpm. After completion of reaction, the reactor was cooled to room temperature in an ice-water bath and the remaining synthesis gas was carefully released in a well ventilated fume hood. Quantitative estimation of the composition of the reaction mixture was analyzed by gas chromatography and further confirmed by GC-MS. General procedure for the cross-coupling reaction A mixture of 4-bromotoluene (0.0410 g, 0.242 mmol, 1 eq.) and phenylboronic acid (0.0354 g, 0.29 mmol, 1.2 eq.), 0.2 mL of a stock solution prepared from dissolving palladium complex 1 (0.002 g, 0.05 mol%) in 2 mL CH3CN, K2CO3 (0.050 g, 0.363 mmol, 1.5 eq.) and methanol (3 mL) was heated under microwave irradiation at 85 °C and 60 watts for 5 minutes to give 4-methyl-1,1′-biphenyl. The substrate scope with different aryl bromides and different boronic acids was tested using the same procedure as above. The molar ratio of the reaction components in all cases were aryl halide, aryl boronic acid, K2CO3, precatalyst and methanol 1/1.2/1.5/0.0005/3 mL. The conversion based on aryl bromides was determined by GC using dodecane as an internal standard and products were confirmed by GC-MS. X-ray crystallography A crystal of each of the compounds in the present work suitable for X-ray crystal analysis was mounted on a Cryoloop™ with a drop of Paratone oil and placed in the cold nitrogen stream of the Kryoflex™ attachment of the Bruker APEX CCD diffractometer. Full spheres of data were collected using a


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combination of three sets of 400 scans in ω (0.5° per scan) at φ = 0, 90 and 180° plus two sets of 800 scans in φ (0.45° per scan) at ω = −30 and 210° under the control of the APEX2 program suite.40 The raw data were reduced to F2 values using the SAINT+ software41 and global refinements of unit cell parameters using ca. 9000 reflections chosen from the full data sets were performed. Multiple measurements of equivalent reflections provided the basis for empirical absorption corrections as well as corrections for any crystal deterioration during the data collection for 2, 4, 9 and 10 while numerical (Gaussian integration) absorption corrections were performed on 3, 4a, 11 and 12 (SADABS42 and TWINABS43). The structures 2, 3, 4 and 4a were solved by direct methods, while 9–12 were solved by Patterson methods and refined by full-matrix leastsquares procedures using the SHELXTL program package.44,45 Hydrogen atoms were placed in calculated positions and included as riding contributions with isotropic displacement parameters tied to those of the attached non-hydrogen atoms. Crystal data and refine parameters are shown in Table 8. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC 955814–955821.

Acknowledgements We are grateful to the Department of Science and Technology (DST), New Delhi, for financial support of this work through grant no. SR/S1/IC-17/2010. We thank UGC and CSIR New Delhi for a Senior Research Fellowship (SRF). We also thank SAIF and Department of Chemistry, Indian Institute of Technology Bombay, Mumbai for instrumentation facilities as well as spectral and analytical data. J.T.M. thanks the Louisiana Board of Regents for purchasing the CCD diffractometer and the Chemistry Department of Tulane University for support of the X-ray laboratory. We thank Shoeb R. Khan for useful discussions during hydroformylation reactions. We thank the referees for their comments and suggestions. The reviewer’s suggestions at the revision stage were very helpful.

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