Direct Observation of the Intermediates in the Photochemical Reaction of R3SiCo(CO)4 with R'3SiH and Establishment of the Mechanism for R'3SiCo(CO)4 Formation

Article abstract of DOI:10.1021/ja00316a030

Irradiation of R3SiCo(CO)4 in the presence of R'3SiH yields R'3SiCo(CO)4 and R3SiH at 298 K in an alkane solvent.The mechanism for this reaction has been established by irradiation at low temperature in alkane media.At 77 K in a rigid alkane medium, irradiation of R3SiCo(CO)4 (R = Me, Et, Ph) yields dissociative loss of CO to give a 16 e^- complex, R3SiCo(CO)3, as determined by infrared spectroscopy.If the matrix contains a sufficiently high concentration of R3SiH (R = Et) the light-induced loss of CO occurs, but the metal carbonyl product is (R3Si)(R'3Si)Co(CO)3H.This species can also be formed photochemically at 196 K in fluid solution.The (Et3Si)2Co(CO)3H is sufficiently inert that the Co-hydride resonance in the 1H NMR can be observed at δ 9.8.Warmup of the (R3Si)(R'3Si)Co(CO)3H to 298 K results in generation of both R3SiCo(CO)4 and R'3SiCo(CO)4.The low-temperature photochemistry thus provides direct evidence for both the 16 e^- primary photoproduct and the Co(III) oxidative addition product in the exchange mechanism.