Scope and Mechanism of the Intermolecular Addition of Aromatic Aldehydes to Olefins Catalyzed by Rh(I) Olefin Complexes

Rhodium (I) bis-olefin complexes Cp*Rh(VTMS)2 and Cp⧧Rh(VTMS)2 (Cp* = C5Me5, Cp⧧ = C5Me4CF3, VTMS = vinyl trimethylsilane) were found to catalyze the addition of aromatic aldehydes to olefins
to form ketones. Use of the more electron-deficient catalyst Cp⧧Rh(VTMS)2 results in faster reaction rates,
better selectivity for linear ketone products from α-olefins, and broader reaction scope. NMR studies of the
hydroacylation of vinyltrimethylsilane showed that the starting Rh(I) bis-olefin complexes and the
corresponding Cp*/⧧Rh(CH2CH2SiMe3)(CO)(Ar) complexes were catalyst resting states, with an equilibrium
established between them prior to turnover. Mechanistic studies suggested that Cp⧧Rh(VTMS)2 displayed
a faster turnover frequency (relative to Cp*Rh(VTMS)2) because of an increase in the rate of reductive
elimination, the turnover-limiting step, from the more electron-deficient metal center of Cp⧧Rh(VTMS)2.
Reaction of Cp*/⧧Rh(CH2CH2SiMe3)(CO)(Ar) with PMe3 yields acyl complexes Cp*/⧧Rh[C(O)CH2CH2SiMe3](PMe3)(Ar); measured first-order rates of reductive elimination of ketone from these Rh(III) complexes
established that the Cp⧧ ligand accelerates this process relative to the Cp* ligand.