title: Interaction of Triphenyltin Hydride and Rhodium. Structure of [Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(2)] and NMR ((1)H, (15)N, (31)P, (103)Rh, (119)Sn) Study of Pyridine-Containing Derivatives.
abstract: The structure of [Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(2)] (1) (formed from [Rh(NCBPh(3))(PPh(3))(3)] and Ph(3)SnH) 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) Å 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) Å; beta = 92.93(2) degrees; V = 6085(2) Å(3); Z = 4; R = 0.050 for 5655 reflections with I >/= 2sigma(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 (4-MeO(2)Cpy) (c)) in dichloromethane at -25 degrees C to give trans-[Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(2)(L)] (2a-c). With L = 4-Me(2)Npy, the products cis-[Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(2)(4-Me(2)Npy)] (3) and cis- and trans-[Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(4-Me(2)Npy)(2)] (4 and 5, respectively) are also formed. At room temperature, [Rh(NCBPh(3))(H)(SnPh(3))(PPh(3))(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 PPh(3) originating from 1) undergoes reductive elimination of Ph(3)SnH to give cis-[Rh(NCBPh(3))(PPh(3))(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 Ph(3)SnH from 6b (L = 4-Me(2)Npy) gave activation parameters DeltaH() = 97 +/- 6 kJ mol(-)(1) and DeltaS() = 1 +/- 20 J K(-)(1) mol(-)(1). The weakened interaction between Ph(3)SnH and rhodium is accounted for in terms of a three-center "agostic" bond.
authors.affiliation: Centre for Molecular Design, Department of Chemistry, University of the Witwatersrand, Johannesburg, Republic of South Africa.
authors.forename: Laurence
authors.initials: L
authors.lastname: Carlton
authors.forename: Rosemarie
authors.initials: R
authors.lastname: Weber
authors.forename: Demetrius C.
authors.initials: DC
authors.lastname: Levendis