The nickel-catalyzed reactions of 1,2-bis(dimethylsilyl)carborane 1 with aldehydes such as isobutyraldehyde, trimethylacetaldehyde, hexanal, and benzaldehyde afforded 5,6carboranylene-2-oxa-1,4-disilacyclohexanes. The dehydrogenative 1,4-double silylation of methacrolein and trans-4-phenyl-3-buten-2-one in the presence of a catalytic amount of Ni-(PEt 3 ) 4 took place under similar conditions. In contrast, the reaction of 1 with R-methyltrans-cinnamaldehyde and trans-cinnamaldehyde under the same reaction conditions yielded the insertion compounds formed via insertion of a carbonyl group into each of the C-Si bonds of 1. The reaction of 1 with diphenylketene gave the 1,2-adduct across the carbonyl group. The structures of compounds 8, 11, and 14 were determined by single-crystal X-ray crystallography.
Recently, Tanaka and co-workers 8 reported that a metal complex catalyzed double silylation of transcinnamaldehyde with o-bis(dimethylsilyl)benzene afforded 1,2 and 1,4 adducts C. The peculiar behavior of the 1,2-bis(dimethylsilyl)carborane 1 has allowed novel transformations of some carbonyl compounds. The double silylation of the carbonyl by the cyclic bis(silyl)platinum complex was a stoichiometric process and thus was limited. Accordingly, we have started a systematic study of the double silylation of carbonyl compounds catalyzed by a nickel complex. Here we report the double silylation reactions of carbonyl compounds such as aldehydes, R,ฮฒ-unsaturated aldehydes, R,ฮฒ-unsaturated ketones, and a ketene with 1,2-bis(dimethylsilyl)carborane.
Results and Discussion
Nickel-Catalyzed Reactions with Aldehydes. Although the platinum complex (C 2 H 4 )Pt(PPh 3 ) 2 is not a catalyst for the 1,2-double silylation of aldehydes when 1,2-bis(dimethylsilyl)carborane 1 is used, due to its