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Relevant academic research and scientific papers

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

Silylation of ethylene by the chlorosilanes HSiMe2Cl and HSiMeCl2 was catalysed by the bis(dihydrogen) complex RuH 2(η2-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 RuH2(η2-H2)(η2- HSiMe2Cl)(PCy3)2 (2Me2Cl), RuH 2(η2-HSiMe2Cl)2(PCy 3)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-H 2)(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 3MeCl 2 and 4MeCl2 were detected as well as traces of 2MeCl 2. 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)(SiMe 3-nCln)2(PCy3) (6Me 3-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(SiMe 2Cl)(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), C2H3SiMe 2Cl 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.

Activation of chlorosilanes at ruthenium: A route to silyl σ-dihydrogen complexes

The hydrido σ-dihydrogen complex RuClH(η2-H 2)(PCy3)2 (2) reacts with the chlorosilanes HSiMe3-nCln (n = 1-3) to form the corresponding silyl σ-dihydrogen complexes RuCl(SiMe3-nCln) (η2-H2)(PCy3)2 (3Me 3-nCln). These complexes display a 16-electron configuration, as shown by NMR, by X-ray data in the case of 3MeCl2, and by theoretical calculations. The σ-H2 ligand in 3MeCl 2 has been located by X-ray diffraction, and the H-H distance of 1.05(3) A compares well with the value obtained by DFT/ B3PW91 (1.073 A) as well as with the value of 1.08 ± 0.01 A derived from the measurement of the JHD coupling constant of 17.5 Hz for the deuterated isotopomer RuCl(SiMeCl2)(η2-HD)(PCy 3)2. The series of model complexes RuCl(SiMe 3-nCln)(η2-H2)(PMe 3)2 (S3Me3-nCln) was investigated by DFT at the B3PW91 level. The most stable isomers have a structure that resembles the X-ray structure of 3MeCl2: i.e., a silyl σ-dihydrogen formulation. In the case of S3Me2Cl and S3MeCl2 a second minimum very close in energy was optimized and formulated as a hydrido σ-silane species. The influence of the number of Cl substituents on Si and their location have been analyzed. The difference between 3Me2Cl on one side and 3MeCl2 and 3Cl3 on the other side is highlighted both by NMR and DFT data and by their reactivity toward ethylene. No reaction was observed for the latter complexes, whereas reaction with 3Me2Cl produces the hydrido η2-ethylene complex RuClH(C2H4)(PCy 3)2 (4). In the case of styrene, the arene complex RuCl(SiMe2Cl)(η6-C8H10)(PCy 3) (5) was isolated.