NOVEL REACTION OF SILYL CARBONYL-COMPLEXES WITH HYDRIDE-TRANSFER REAGENTS - REDUCTION OF A CARBONYL LIGAND AND COUPLING WITH A SILYL GROUP

Treatment of CpFe(CO)(2)SiR3 (Cp = eta(5)-C5H5; R-3 = (p)Tol(2)Cl, (p) Tol(2)H, (p)Tol(2)Me, MePh (1-Nap), and (n-C5H11)(2)H; 1-Nap = 1-napht hyl) with LiAlH4 in ether or THF at room temperature gave CH3SiR3 as t he major product in moderate to high yield together with HSiR3. Reacti on of CpFe(CO)(2)SiMes(2)H with LiAlH4 afforded only H(2)SiMes(2). Lab eling experiments using LiAlD4 gave the deuterated methylsilanes. Thes e results proved that the hydrogen source for the methyl group is LiAl H4. Furthermore, the reduction of CpFe(CO)(2)Si(p)Tol(2)R' (*C = C-13 enriched; R' = H,Me) produced CH(3)Si(p)Tol(2)R' where the methyl gr oup introduced on Si was C-13-enriched. These experimental results sug gested that the carbonyl ligand was reduced by LiAlH4 and coupled with the silyl group to give the methylsilane. CpFe(CO)(2)Si(p)Tol(2)H (C p = eta(5)-C5Me5), having a Cp* ligand which is bulkier and more elec tron-donating than a Cp ligand, did not react with LiAlH4 at room temp erature, but it did so at 50 degrees C to give CH(3)Si(p)Tol(2)H and H Si(p)Tol(2)H, probably because nucleophilic attack of LiAlH4 at a carb onyl ligand was retarded both sterically and electronically by the Cp ligand. When the :reactions were performed in sealed NMR tubes and mo nitored by NMR spectroscopy, the signals due to the anionic complexes Li+[CpFe(CO)(CH3)Si(p)Tol(2)R'](-) were observed in addition to those of silane products. These anionic complexes are considered not to be i ntermediates but to be byproducts because the anionic complexes did no t change to methylsilanes on heating. The anionic complexes reacted wi th MeOH and Mel to give hydrosilanes HSi(p)Tol(2)R' and methylsilanes CH(3)Si(p)Tol(2)R', respectively.