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Highly Selective Dehydrogenative Silylation of Alkenes Catalyzed by Rhenium Complexes
Author(s) -
Jiang Yanfeng,
Blacque Olivier,
Fox Thomas,
Frech Christian M.,
Berke Heinz
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200802019
Subject(s) - rhenium , silylation , chemistry , phosphine , hydride , hydrosilylation , medicinal chemistry , catalysis , substituent , stereochemistry , ethylene , organic chemistry , metal
Choosy chemicals : Rhenium(I) complexes of type [ReBr 2 (L)(NO)(PR 3 ) 2 ] (L=H 2 ( 1 ), CH 3 CN ( 2 ), ethylene ( 3 ); R= i Pr ( a ), cyclohexyl ( b )) proved to be suitable catalyst precursors for the highly selective dehydrogenative silylation of alkenes. Two types of rhenium(I) hydride species, [ReBrH(NO)(PR 3 ) 2 ] ( 4 ) and [ReBr(η 2 ‐CH 2 CHR 1 )H(NO)(PR 3 ) 2 ] ( 5 ), were found in the [ReBr 2 (L)(NO)(PR 3 ) 2 ]‐catalyzed dehydrogenative silylation of alkenes.Rhenium(I) complexes of type [ReBr 2 (L)(NO)(PR 3 ) 2 ] (L=H 2 ( 1 ), CH 3 CN ( 2 ), and ethylene ( 3 ); R= i Pr ( a ) and cyclohexyl (Cy; b )) catalyze dehydrogenative silylation of alkenes in a highly selective manner to yield silyl alkenes and the corresponding alkanes. Hydrosilylation products appear only rarely depending on the type of olefinic substituent, and if they do appear then it is in very minor amounts. Mechanistic studies showed that two rhenium(I) hydride species of type [ReBrH(NO)(PR 3 ) 2 ] (R= i Pr ( 4 a ) and Cy ( 4 b )) and [ReBr(η 2 ‐CH 2 CHR 1 )H(NO)(PR 3 ) 2 ] (R 1 = p ‐CH 3 C 6 H 4 , R= i Pr ( 5 a ), Cy ( 5 b ); R 1 =H, R= i Pr ( 5 a′ ), Cy ( 5 b′ )) are involved in the initiation pathway of the catalysis. The rate‐determining steps of the catalytic cycle are the phosphine dissociation from complexes of type 5 and the reductive eliminations to form the alkane components. The catalytic cycle implies that the given rhenium systems have the ability to activate CH and SiH bonds through the aid of a facile redox interplay of Re I and Re III species. The molecular structures of 4 b and 5 a were established by means of X‐ray diffraction studies.