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Keywords:

  • copolymerization;
  • heterogeneous catalysis;
  • homogeneous catalysis;
  • hydrosilylation;
  • mesoporous materials;
  • rhodium

Abstract

The preparation of 1-(3-triisopropoxysilylpropyl)-3-(2-methoxyethyl)-imidazolium bromide or chloride salts and their reaction with [Rh(COD)(μ-OMe)]2 (COD=1,5-cyclooctadiene) to afford the corresponding [Rh(COD)(NHC)X] (X=Br, Cl; NHC=1-(3-triisopropoxysilylpropyl)-3-(2-methoxyethyl)-2-ilydene-imidazol) species is described. These new compounds were used as catalyst precursors for acetophenone hydrosilylation. The higher activity of the rhodium-chlorido complex evidences a clear halide effect in the activation of the catalyst. Immobilization of the catalytic precursor [Rh(COD)(NHC)Cl] on mobile crystalline material 41 (MCM-41) allows for the preparation of the corresponding heterogeneous catalyst. Reduction of acetophenone to PhMeCH-O-SiMe(OSiMe3)2 by hydrosilylation with 1,1,1,3,5,5,5-heptamethyltrisiloxane is effectively catalyzed by both the homogeneous and the heterogeneous catalysts, in which the homogeneous system is the more active. Interestingly, the heterogeneous catalyst is reusable. Both homo- and heterogeneous catalysts are also effective for the copolymerization of terephthalaldehyde and 1,1,3,3,5,5-hexamethyltrisiloxane, which affords the corresponding poly(silyl ether). The catalyst yields the heterogeneous system polymers with higher molecular weights (Mw=94 000 g mol−1) and a narrow molecular weight distribution (PDI=1.5–1.7).