Stoichiometric and catalytic activation of Si-H bonds by a triruthenium carbonyl cluster, (μ₃,η²:η³:η ⁵-acenaphthylene)Ru₃(CO)₇: Isolation of the oxidative adducts, catalytic hydrosilylation of aldehydes, ketones, and acetals, and catalytic polymerization of cyclic ethers

Treatment of the ruthenium cluster (μ₃,η²:η³:η ⁵-acenaphthylene)Ru₃(CO)₇ (1) with stoichiometric amounts of trialkylsilanes results in liberation of a CO ligand followed by oxidative addition of a Si-H bond. The trinuclear silyl complexes (μ₃,η²:η³:η ⁵-acenaphthylene)-Ru₃(H)(SiR₃)(CO)₆ (2) were isolated in good yield. They were characterized by NMR spectroscopy and X-ray crystallography. Compound 1 catalyzes the hydrosilylation of olefins, acetylenes, ketones, and aldehydes. In particular, the reactions of aldehydes and ketones proceed at room temperature to form the corresponding silyl ethers in good yield; the catalytic activities are superior to those with RhCl(PPh₃)₃. The RhCl(PPh₃)₃-catalyzed hydrosilylation of ketones with Me₂(H)SiCH₂CH₂Si(H)Me₂ results in selective reaction of only one Si-H terminus, while similar reactions, when catalyzed by 1, allow utilization of both Si-H groups. Significantly different regio- and stereoselectivities, compared with those obtained in reactions catalyzed by RhCl(PPh₃)₃, also were observed in the hydrosilylation of α,β-unsaturated carbonyl compounds and 4-tert-butylcyclohexanone, respectively. The reactions with acetals and cyclic ethers also take place under similar conditions. The reaction of trialkylsilanes with an excess of a cyclic ether resulted in ring-opening polymerization. Polymerization of THF was investigated as a representative example. Treatment of trialkylsilanes with an excess of THF (10-10² equiv with respect to silanes) in the presence of a catalytic amount of 1 resulted in production of polytetrahydrofuran with M_n = 1000-200 000 and M_w/M_n = 1.3-2.0. Changing the ratio of THF to HSiR₃ can control the molecular weight. NMR studies suggested that the structure of the polymer is R₃SiO-[(CH₂)₄O]_n-CH ₂CH₂CH₂CH₃. Mechanistic considerations based on differences in the catalytic activities between the catalysts 1 and 2 are discussed.