A Bowl-Shaped Phosphine as a Ligand in Rhodium-Catalyzed Hydrosilylation: Rate Enhancement by a Mono(phosphine) Rhodium Species

Bowl-shaped phosphine (BSP) ligands markedly accelerated the rhodium-catalyzed
hydrosilylation of ketones and ketimines as compared with the effect of conventional
phosphine ligands such as PPh3 and P(t-Bu)3. 31P NMR study of a mixture of [RhCl(C2H4)2]2
and phosphines at various P/Rh ratios revealed that coordination of BSP to the rhodium
metal was successfully regulated, and the resultant rhodium complex bearing only one
phosphine ligand (a mono(phosphine) rhodium species) was responsible for the acceleration.
Structural comparison between BSP and the conventional phosphines was carried out using
HF/6-31G(d)-CONFLEX/MM3-optimized structures. The mono(phosphine) rhodium complex
having 1,5-cyclooctadiene as a ligand was isolated, and its X-ray molecular structure was
determined.