SILYLFORMYLATION OF 1-HEXYNE CATALYZED BY RHODIUM-COBALT MIXED-METAL CARBONYL CLUSTERS

Reactions of hydrosilanes with 1-hexyne catalyzed by Co2Rh2(CO)12 and Rh4(CO)12 at 25-degrees-C and atmospheric pressure-150 psi of carbon monoxide give (Z)-1-silyl-2-formyl-1-hexenes (1), which are the products of "silylformylation", and/or (E)-1-silyl-1-hexenes (2). The ratio of silylformylation vs hydrosilylation products depends on the electronic nature of hydrosilane used. Depending on the conditions, the reaction gives 2,4-di-n-butyl-3-silylcyclopent-2-en-1-one (3) as a major side product, which is a unique carbometalation-cyclization product. The novel Rh-Co mixed-metal complexes (PhMe2Si)2Rh-(CO)nCO(CO)4 (n = 2, 3); 6a and RhCo(n-BuC = CH)(CO)5 (7) are found to be important catalyst species for silylformylation catalyzed by Co2Rh2(CO)12. Possible catalytic cycles of silylformylation that can accommodate the observed results are proposed.