I. Gridnev, Natsuka Higashi, A. K. Asakura
Jul 18, 2000
Citations
0
Influential Citations
141
Citations
Quality indicators
Journal
Journal of the American Chemical Society
Abstract
The mechanism of asymmetric hydrogenation catalyzed by a new effective catalyst, viz., a rhodium complex of (S,S)-1,2-bis(tert-butylmethylphosphino)ethane (BisP*), has been studied by multinuclear NMR. Hydrogenation of the precatalyst [Rh(BisP*)(nbd)]BF4 (8) at −20 °C in deuteriomethanol affords solvate complex [Rh(BisP*)(CD3OD)2]BF4 (9), which is, in turn, hydrogenated at −90 °C producing equilibrium amounts (20% at −95 °C) of [RhH2(BisP*)(CD3OD)2] (10)the first observable dihydride of a Rh(I) complex with a diphosphine ligand. Dihydride 10 is in equilibrium with 9 and dihydrogen, which was studied in the temperature interval from −100 to −50 °C, yielding thermodynamic parameters ΔH = −6.3 ± 0.2 kcal M-1 and ΔS = −23.7 ± 0.7 cal M-1 K-1. The hydrogenation of 9 is stereoselective: two isomers 10a and 10b are produced in a ratio 10:1. Use of HD for the hydrogenation of 9 yields the isomers with deuterium cis and trans to the phosphine in a ratio 1.3 (±0.1):1. The thermodynamic parameters of the equilibriu...