Interaction of triphenyltin hydride and rhodium.: Structure of [Rh(NCBPh3)(H)(SnPh3)(PPh3)2] and NMR (1H,15N, 31P, 103Rh, 119Sn) study of pyridine-containing derivatives

The structure of [Rh(NCBPh3)(H)(SnPh3)(PPh3)(2)] (1) (formed from [Rh(NCBPh3)(PPh3)(3)] and Ph3SnH) was determined by a single-crystal X-ray diffraction study which shows the geometry to be equally well described as a distorted tetragonal pyramid with tin at the apex or a distorted trigonal bipyramid with a hydrogen of one of the phosphine phenyl groups occupying the sixth coordination site. The tin-hydride distance of 2.31(5) Angstrom is consistent with a weak interaction. Crystal data for 1: space group, P2(1)/c; a = 12.564(4), b = 26.942(4), c = 18.000(3) Angstrom; beta = 92.93(2)degrees; V = 6085(2) Angstrom(3); Z = 4; R = 0.050 for 5655 reflections with I greater than or equal to 2 sigma(I). Complex 1 reacts with pyridine and substituted pyridines L (L = pyridine (py) (a), 4-(dimethylamino)pyridine (4-Me(2)Npy) (b), and 4-carbomethoxypyridine (CMeO(2)Cpy) (c)) in dichloromethane at -25 degrees C to give trans-[Rh(NCBPh3)(H)(SnPh3)-(PPh3)(2)(L)] (2a-c). With L = 4-Me(2)Npy, the products cis-[Rh(NCBPh3)(H)(SnPh3)(PPh3)(2)(4-Me(2)Npy)] (3) and cis- and trans-[Rh(NCBPh3)(H)(SnPh3)(PPh3)(4-Me(2)Npy)(2)] (4 and 5, respectively) are also formed. At room temperature, [Rh(NCBPh3)(H)(SnPh3)(PPh3)(L)] (6a-c) is the final product, decomposing over a period of hours. The pyridine-containing complexes were not isolated and were characterized by NMR spectroscopy, which showed the magnitude of the spin coupling constant J(Sn-H) to increase by factors of up to 5.5 compared with the value of 29 Hz observed for 1. At 50 degrees C, 6 (in the presence of L and PPh3 originating from 1) undergoes reductive elimination of Ph3SnH to give cis-[Rh(NCBPh3)(PPh3)(2)(L)]; at this temperature 1 is stable, decomposing only at temperatures of 85 degrees C and above. A kinetic study of the dissociation of Ph3SnH from 6b (L = 4-Me(2)Npy) gave activation parameters Delta H double dagger = 97 +/- 6 kJ mol(-1) and Delta S double dagger = 1 +/- 20 J K-1 mol(-1). The weakened interaction between Ph3SnH and rhodium is accounted for in terms of a three-center "agostic" bond.