Rhodium-hydrogen-tin three-center bonds.: NMR (1H, 31P, 103Rh, 119Sn) study of [Rh(Cl)(H)(SnPh3)(PPh3)(py)] and related compounds

The complex trans- [Rh(NCBPh3)(H)(SnPh3) (PPh3)(2)] (1) reacts with pyridine and substituted pyridines (L) in dichloromethane at 22 degrees C to give [Rh(NCBPh3)(H)(SnPh3)(PPh3)(L)] (2a) and at -25 degrees C to give trans-[Rh(NCBPh3)(H)(SnPh3)(PPh3)(2)(L)] (3a). These complexes and numerous analogues can be prepared (the majority in solution only) by the reactions of [Rh(X)(PPh3)(3)] (X = NCBPh3 (a), N(CN)(2) (b), NCS (c), N-3 (d), NCO (e), O2CCF3 (f), Cl (g)) with Ph3SnH in solutions containing pyridines (4-Rpy; R = CO2Me, H, NMe2), 1-methylimidazole (1-Meim), and benzonitriles (4-RC6H4CN; R = COMe, H, NMe2) (L). NMR data for the series of complexes 2 in which ligands X, L, and, for X = Cl, the phosphine P(4-C6H4R)(3) (R = F, H, Me) were varied independently show systematic changes in the parameters delta(Sn-119), delta(Rh-103), J(Sn-119-H-1), and J(Rh-103-Sn-119, which are related to the electron-donating properties of X, L, and the phosphine. Plots of J(Sn-119-H-1) against delta(Sn-119), delta(Rh-103), and J(Rh-103-Sn-119) are approximately linear and show delta(Rh-103) and J(Rh-103-Sn-119) increasing with J(Sn-119-H-1) and delta(Sn-119) decreasing. Complexes 3 give higher values of J(Sn-119-H-1) and lower values of delta(Sn-119) than found for the less electron-rich 2, with data for 3 continuing the trends in J(Sn-119-H-1) and delta(Sn-119) observed for 2. Values of delta(Rh-103) and J(Rh-103-Sn-119) for 3 do not match the pattern found for 2; nor do data for an isomeric form of 3, cis-[Rh(Cl)(H)(SnPh3)(PR3)(2)(L)] (L = benzonitriles) (4). The plot of J(Sn-119-H-1)/delta(Sn-119) for 3 shows discontinuities at high values of J(Sn-119-H-1), with the trend in delta(Sn-119) toward more negative values las the ligands become more nucleophilic) being transformed into an increase and changes in J(Sn-119-H-1) becoming smaller. These patterns of NMR data are interpreted in terms of the weakening of an Rh-(H-Sn) three-center interaction and changes in the coordination geometry of tin as the electron density on rhodium is increased.