- Cross-Metathesis of Vinylsilanes with Styrene Catalyzed by Ruthenium-Carbene Complexes
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The cross-metathesis of styrene with various vinylsilanes, H2C=C(H)SiR3, catalyzed by [Cl2(PCy3)2Ru=CHPh] (1) to give (E)-silylstyrene, (E)-Ph(H)C=C(H)SiR3, and ethylene is reported. The reaction proceeds even at room temperature and is highly selective. Very high conversions are observed when R = OEt, OSiMe3 (≥95%, 6 h, 2 mol % of 1). The conversion significantly decreases with increasing substitution of Me for OR′. The metathesis is reversible. Therefore, removal of ethylene is critical for achieving high conversions. From the study of stoichiometric reactions of 1 with vinylsilanes it follows that in the series SiR3 = Si(OEt)3, SiMe(OEt)2, SiMe2OEt, SiMe3 and SiR3 = Si(OSiMe3)3, SiMe(OSiMe3)2, SiMe2-(OSiMe3), SiMe3 the conversion rate increases, but simultaneously the selectivity of the metathesis decreases. The decreasing selectivity readily accounts for the decreasing efficiency in the catalytic metathesis. The product distribution of reactions of styrene-d8 with H2C= C(H)SiR3 (R = OEt, OSiMe3) in the presence of 1 provides evidence for a metallacarbene mechanism involving [Ru]=CHPh and [Ru]=CH2 species.
- Pietraszuk, Cezary,Marciniec, Bogdan,Fischer, Helmut
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- METAL COMPLEXES FOR USE IN OLEFIN METATHESIS AND ATOM GROUP TRANSFER REACTIONS
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Improved catalysts useful in a number of organic synthesis reactions such as olefin metathesis and atom or group transfer reactions are made by bringing into contact amulti-coordinated metal complex comprising a multidentate Schiff base ligand, and one or more other ligands, with an acid under conditions such that said acid is able to at least partly cleave a bond between the metal and the multidentate Schiff base ligand of said metal complex, optionally through intermediate protonation of said Schiff base ligand.
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