The catalytic potential of carbon nucleophiles has seldom been disclosed due to their reactivity toward carbon electrophiles to form stable carbon-carbon bonds,which are too strong to be cleaved for the expected catalytic cycles. We have developed an efficient catalytic cyanosilylation of carbonyl compounds with an in situ generated alkene/phosphine adduct,which is tuned not to couple with a carbonyl compound or an electron-deficient alkene under the reaction conditions when its nucleophilicity is trans-lated into catalytic activity. In the presence of 3 mol% of methyl acrylate and 3 mol% of triphenylphosphine,a broad range of alkyl,alkenyl,and aryl ketones and aldehydes undergo cyanosilylation reaction with trimethylsilyl cyanide at room temperature to yield structurally diversified cyanohydrin silyl ethers in excellent yields. By using methyl acrylate/triphenylphosphine as a highly effective nucleophilic catalyst system for the cyanosilylation of carbonyl compounds,this study demonstrates a new concept for the development of useful organocatalysis utilizing the nucleophilicity of alkene/phosphine adducts generated in situ. The catalytic potential of carbon nucleophiles has seldom been due due to their reactivity toward carbon electrophiles to form stable carbon-carbon bonds, which are too strong to be cleaved for the expected catalytic cycles. We have developed an efficient catalytic cyanosilylation of carbonyl compounds with an in situ generated alkene / phosphine adduct, which is tuned not to couple with a carbonyl compound or an electron-deficient alkene under the reaction conditions when its nucleophilicity is trans-lated into catalytic activity. In the presence of 3 mol% of methyl acrylate and 3 mol% of triphenylphosphine, a broad range of alkyl, alkenyl, and aryl ketones and aldehydes undergo cyanosilylation reaction with trimethylsilyl cyanide at room temperature to yield structurally diversified cyanohydrin silyl ethers in excellent yields. By using methyl acrylate / triphenylphosphine as a highly effective nucleophilic catalyst system for the cyanosilylation of carbonyl compounds, this study demonst rates a new concept for the development of useful organocatalysis utilizing the nucleophilicity of alkene / phosphine adducts generated in situ.