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Issue 36, 2010
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Silyl and σ-silane ruthenium complexes: Chloride substituent effects on the catalysed silylation of ethylene

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Abstract

Silylation of ethylene by the chlorosilanes HSiMe2Cl and HSiMeCl2 was catalysed by the bis(dihydrogen) complex RuH22-H2)2(PCy3)2 (1). Dehydrogenative silylation leading to the formation of the corresponding vinylsilanes was in competition with hydrosilylation. The rate and selectivity of the reactions were influenced by the number of chloro substituents and the ethylene pressure. A comparative mechanistic study was performed in toluene-d8 with the two chlorosilanes. Reaction of 1 with an excess of HSiMe2Cl (10 equiv.) produced the σ-silane complexes RuH22-H2)(η2-HSiMe2Cl)(PCy3)2 (2Me2Cl), RuH22-HSiMe2Cl)2(PCy3)2 (3Me2Cl) and the silyl complex RuCl(SiMe2Cl)(η2-H2)(PCy3)2 (4Me2Cl), all characterised by multinuclear NMR spectroscopy. Complexes 2Me2Cl and 3Me2Cl adopt a cis configuration for the two bulky phosphine ligands as a result of stabilising SISHA (Secondary Interactions between Silicon and Hydrogen Atoms) interactions. Complex 4Me2Cl resulted from the stoichiometric reaction of HSiMe2Cl with 1 producing RuHCl(η2-H2)(PCy3)2in situ which further reacted with evolution of H2 and formation of 4Me2Cl. When reacting 1 with 10 equiv. of HSiMeCl2, the corresponding complexes 3MeCl2 and 4MeCl2 were detected as well as traces of 2MeCl2. The reactivity toward ethylene was then examined. Under catalytic conditions (excess silane in toluene-d8, ethylene atmosphere) only two compounds could be characterised: free PCy3 and the new (η6-aryl)(disilyl) complexes of the general formula Ru(η6-C6D5CD3)(SiMe3−nCln)2(PCy3) (6Me3−nCln-d8, n = 1,2). The X-ray structure of 6MeCl2 was obtained on a single-crystal at 160 K. When only 2 equiv. of HSiMe2Cl were added, the ethylene(silyl) complex RuH(SiMe2Cl)(C2H4)(PCy3)2 (7Me2Cl) was obtained in addition to the organic products resulting from catalytic hydrogenation, hydrosilylation and dehydrogenative silylation, i.e. C2H6 (major one), C2H3SiMe2Cl and C2H5SiMe2Cl. In the case of 2 equiv. of HSiMeCl2, upon ethylene addition, 7MeCl2 was formed in minority compared to a new disilyl complex Ru(SiMeCl2)2(PCy3)2 (8MeCl2) characterised by NMR spectroscopy and X-ray diffraction on a single crystal at 160 K. In 8MeCl2, a formal 14-electron species, stabilisation through two agostic C–H bonds of the cyclohexyl groups was ascertained by DFT calculations.

Graphical abstract: Silyl and σ-silane ruthenium complexes: Chloride substituent effects on the catalysed silylation of ethylene

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Publication details

The article was received on 03 Mar 2010, accepted on 01 Jun 2010 and first published on 09 Jul 2010


Article type: Paper
DOI: 10.1039/C0DT00065E
Citation: Dalton Trans., 2010,39, 8492-8500
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    Silyl and σ-silane ruthenium complexes: Chloride substituent effects on the catalysed silylation of ethylene

    S. Lachaize, L. Vendier and S. Sabo-Etienne, Dalton Trans., 2010, 39, 8492
    DOI: 10.1039/C0DT00065E

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