ON THE MECHANISM OF SILYLFORMYLATION CATALYZED BY RH-CO MIXED-METAL COMPLEXES

Possible mechanisms for the silylformylation of 1-alkynes catalyzed by Rh2Co2(CO)(12) are investigated. Novel Rh-Co mixed metal complexes, ( PhMe2Si)(2)Rh(CO)(n)Co(CO)(4) (n=2 or 3) (3) and RhCo(HC=CBun)(CO)(5) (5), are found to play important roles in this catalysis. The reaction of 3 with 1-hexyne and HSiMe2Ph at ambient temperature and pressure o f CO gives n-BuC(CHO)=CHSiMe2Ph (1a, Z/E = 95/5), (PhMe2Si)(2)Rh(CO)(3 )Co(CO)(4) (3-B) and an Rh-Co mixed metal butterfly complex, Rh2Co2(HC =CBun)(CO)(10)(4). The reaction of 5 with 1-hexyne and HSiMe,Ph under the same ambient conditions affords la ( 100% Z) very cleanly as the s ole reaction product. The crossover experiments using RhCo(DC=CBun)(CO )(5) (5-d), 1-hexyne-1d and DSiMe2Ph strongly support the mixed metal bimetallic catalysis, and involvement of bis(alkyne)-Rh-Co species. Th e most plausible catalytic cycle of silylformylation which can accommo date all the observed results is proposed. (C) 1998 Elsevier Science S .A.