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 CpRh(VTMS)(2) (Cp* = C(5)Me(5), Cp = C(5)Me(4)CF(3), VTMS = vinyl trimethylsilane) were found to catalyze the addition of aromatic aldehydes to olefins to form ketones. Use of the more electron-deficient catalyst CpRh(VTMS)(2) results in faster reaction rates, better selectivity for linear ketone products from alpha-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(CH(2)CH(2)SiMe(3))(CO)(Ar) complexes were catalyst resting states, with an equilibrium established between them prior to turnover. Mechanistic studies suggested that CpRh(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 CpRh(VTMS)(2). Reaction of Cp*/Rh(CH(2)CH(2)SiMe(3))(CO)(Ar) with PMe(3) yields acyl complexes Cp*/Rh[C(O)CH(2)CH(2)SiMe(3)](PMe(3))(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.
Roy
Amy H
AH
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, USA.
Lenges
Christian P
CP
Brookhart
Maurice
M
D000215:Acylation; D000447:Aldehydes / Q000737:chemistry*; D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D007659:Ketones / Q000138:chemical synthesis*; D009942:Organometallic Compounds / Q000737:chemistry; D012238:Rhodium / Q000737:chemistry*
D000447:Aldehydes; D000475:Alkenes; D007659:Ketones; D009942:Organometallic Compounds; D012238:Rhodium