Reactions of (CO)5MnSi(CH3)3 with organic carbonyl compounds

Article abstract of DOI:10.1021/ic50222a028

Reactions of (CO)₅MnSi(CH₃)₃ (1) with organic carbonyl compounds have been investigated as a means of developing new metal-carbon bond-forming reactions. Benzaldehyde and 1 react over 2 weeks at 5°C to give the silyloxyalkyl complex (CO)₅MnCH(C₆H₅)OSi(CH₃)₃ (2) in 65-90% yield, depending upon conditions. Complex 2 undergoes rapid homolysis at 80°C to [(CO)₅Mn]₂ and the diastereomeric pinacol ethers [-CH(C₆H₅)OSi(CH₃)₃]₂ (3a, 3b). Reactions of 1 with p-methoxybenzaldehyde and p-(dimethylamino)benzaldehyde are much faster but yield organometallic products which are much less stable toward homolysis. Compound 1 and butyraldehyde react to yield (CO)₅MnH and the E and Z isomers (3:2 ratio) of butyraldehyde trimethylsilyl enol ether (8, 9). The isolation of (CO)₅MnCOCH(n-C₃H₇)OSi(CH₃) ₃ (14) when this reaction is conducted under 10 atm of CO provides good evidence for the intermediacy of (CO)₅MnCH(n-C₃H₇)OSi(CH₃) ₃. Acetone, cyclohexanone, and 2-methylcyclohexanone similarly react with 1 to yield (CO)₅MnH and trimethylsilyl enol ethers. In the latter case, a mixture of regioisomers is formed which equilibrate due to the (CO)₅MnH present. These reactions are suggested to proceed via rate-determining formation of ion pairs (CO)₅Mn^-+CR(R′)OSi(CH₃)₃. The thermodynamics and relevance of these reactions to catalytic hydrosilylation processes are discussed.