Stoichiometric and Catalytic Activation of Si−H Bonds by a Triruthenium Carbonyl Cluster, (μ3,η2:η3:η5-acenaphthylene)Ru3(CO)7: Isolation of the Oxidative Adducts, Catalytic Hydrosilylation of Aldehydes, Ketones, and Acetals, and Catalytic Polymerization of Cyclic Ethers

Abstract

Treatment of the ruthenium cluster (μ3,η2:η3:η5-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:η5-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 Mn = 1000−200 000 and Mw/Mn = 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−CH2CH2CH2CH3. Mechanistic considerations based on differences in the catalytic activities between the catalysts 1 and 2 are discussed.