1-octene hydrosilylation catalyzed by lanthanide and yttrium hydrides and hydrocarbyls: A mechanistic study and the role of catalyst association

Dimeric lanthanide (Tb, Yb, Lu) and yttrium hydrides, {Cp ' (2)Ln(mu -H)}(2), where Cp ' = t-BUC5H4, and hydrocarbyls {Cp ' (2)Ln(mu -Me)}(2), as well as compounds with different bridging, Cp ' (2)Ln(mu -H)(mu -Me)LnCp ' (2), are efficient and selective catalysts of 1-octene hydrosilylation. Binuclear complexes with Ln(mu -H)(2)Ln and Ln(mu -H)(mu -Alkyl)Ln bridging fragments were found to be the key intermediates in 1-octene hydrosilylation catalyzed by both the hydrides {Cp ' ,Ln(mu -H)}(2) (Ln = Y, Tb, Yb, Lu) and the mixed compounds Cp ' (2)Ln(mu -H)(mu -Me)LnCp '2 (Ln = Y, Lu) in benzene at 75 degrees. Therefore, in this case, the dissociation of the starting dimeric organolanthanide into monomeric species is not required for the catalytic reaction to proceed. Under the conditions employed, the rate law for the hydrosilylation of 1-octene with PhMeSiH2 is V-HS similar to [lanthanide](1)[olefin](1)[silane](0), suggesting rapid hydride transfer from silane to Ln and the rate-limiting addition of Ln-H to olefin. The hydrosilylation of 1-octene with n-Bu2SiH2 is accompanied by olefin dimerization. In the presence of Ph3SiH, Ph2MeSiH, PhMe2SiH, Et3SiH, and Et3GeH, only the dimerization of 1-octene was observed. Alternatively, the lanthanide and yttrium hydrocarbyls {Cp ' (2)Ln(mu -Me)}(2) (Ln = Y, Tb, Yb, Lu) exhibit higher catalytic activity even at room temperature.The initial rate of the 1-octene hydrosilylation with PhMeSiH2 was found to be V-0 similar to [lanthanide](1/2)[olefin](1)[silane](0). In this case, the hydrosilylation seems to involve the formation of highly active monomeric species Cp ' (2)LnH. After several minutes, the hydrosilylation rate sharply decreased because of association of the catalyst.