Oxidative addition of PhMe2SiH to di- and triruthenium carbonyl clusters bearing 4,6,8-trimethylazulene as the bridging ligand was studied in relation to mechanisms of hydrosilylation of ketones catalyzed by these complexes. Reaction of PhMe2SiH with (μ3,η5:η5-4,6,8-trimethylazulene)Ru 3(CO)7 (3) resulted in liberation of a CO ligand, oxidative addition of the Si-H bond, and hydrogenation of one carbon-carbon double bond in the azulene ligand to form a novel 46-electron cluster, (μ2,η3:η5-4,5-dihydro-4,6,8-trimethy lazulene)Ru3(H)(SiMe2Ph)(CO)6 (6). In contrast, (μ2,η3:η5-4,6,8-trimethylazulene)Ru 2(CO)5 (4) reacted with HMe2SiPh to give (μ2,η3:η5-4,5-dihydro-4,6,8-trimethy lazulene)Ru2(CO)5(SiMe2Ph)2 (7), which has a unique Ru→Ru dative bond, by way of oxidative addition of two molecules of PhMe2SiH to the starting diruthenium complex followed by hydrogenation of a carbon-carbon double bond in the azulene ligand. In contrast to the fact that the diruthenium complexes 4 and 7 are not catalytically active, the triruthenium clusters 3 and 6 are catalysts for the hydrosilylation of acetophenone with moderate catalytic activity. NMR observation of intermediates in the catalytic hydrosilylation of acetophenone using 6 as catalyst suggests the existence of a reaction pathway without a cluster fragmentation, in which the triruthenium cluster is involved in the catalytic cycle.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry