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Manganese- and Rhodium-Catalyzed Phenylsilane Hydrosilation−Deoxygenation of Iron Acyl Complexes Cp(L)(CO)FeC(O)R (L = CO, PPh3, P(OMe)3, P(OPh)3; R = CH3, Ph, CHMe2, CMe3)

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journal contribution
posted on 17.04.1998, 00:00 by Zhibiao Mao, Brian T. Gregg, Alan R. Cutler
The manganese carbonyl acyl complexes L(CO)4MnC(O)R (L = CO, R = CH3 (2a); L = CO, R = Ph (2b); L = PPh3, R = CH3 (2c)) are precatalysts for the PhSiH3 hydrosilation−deoxygenation of Cp(CO)2FeC(O)CH3 (1a) to Cp(CO)2FeCH2CH3 (6a). Thus, 2a (4%) and 1.1 equiv of PhSiH3 reduce 1a initially to a mixture of [Cp(CO)2FeCH(CH3)O]3-xHxSiPh (x = 2 (3b), 1 (4b), and 0 (5b)) (7−8 h), which transforms to a mixture of 5b (62%) and 6a (35%) (12 h). Similarly, 2b and PhSiH3 transform 1a to a mixture containing 4% 3b, 22% 4b, 72% 5b, and 2% 6a (30 min), then up to 15−20% 6a (12 h). Use of 2c as the precatalyst selectively yields 71% 4b and 10% 6a (30 min), then up to 19% 6a (5 h). Both 4b and 5b were isolated by size-exclusion chromatography and characterized as mixtures of four stereoisomers, 4b as a pair of enantiomers having a prochiral center and two meso diastereoisomers with pseudoasymmetric centers and 5b as a diastereomeric pair of enantiomers. The PhSiH3 (1.6 equiv)/RhCl(PPh3)3 (3%) system conveniently transforms Cp(L)(CO)FeC(O)R to their alkyl derivatives Cp(L)(CO)FeCH2R. Seven iron acyl complexes were studied (Cp(CO)2FeC(O)R, R = Me, Ph, iPr, tBu; Cp(L)(CO)FeC(O)CH3, L = PPh3, P(OMe)3, and P(OPh)3), which gave 49−87% isolated yields of Cp(L)(CO)FeCH2R. Their modest yields correspond to the presence of byproducts, Cp(CO)2FeCHCH2 (32%) and 4b (14%) with 1a and 10−15% of the vinyl complexes with L = PPh3 and P(OPh)3.