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Acceptor Pincer Chemistry of Osmium: Catalytic Alkane Dehydrogenation by (CF3PCP)Os(cod)(H)

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posted on 11.11.2013, 00:00 by Brian C. Gruver, Jeramie J. Adams, Navamoney Arulsamy, Dean M. Roddick
Syntheses of osmium analogues of acceptor pincer (CF3PCP)­Ru­(II) systems are reported. Treatment of [Et4N]2OsCl6 with CF3PCPH at 130 °C in ethanol in the presence of Et3N gave the coordinatively saturated anionic carbonyl complex HNEt3+[(CF3PCP)­Os­(CO)­Cl2], which subsequently may be converted to cis-(CF3PCP)­Os­(CO)2Cl or cis-(CF3PCP)­Os­(CO)2H by reaction with Me3SiOTf or (Et3Si)2(μ-H)+B­(C6F5)4, respectively. (CF3PCP)­Os­(cod)H was obtained in modest yields by thermolysis of Os­(cod)­(η3-2-methylallyl)2 with CF3PCPH in neat cod under 3 atm of H2 at 130 °C. The alkane dehydrogenation activity of (CF3PCP)­Os­(cod)H was examined: under identical conditions to previously studied (CF3PCP)­Ru­(cod)­H (1:1 cyclooctane/tert-butylethylene, 200 °C), the initial turnover rate for cyclooctene production was 1520 h–1, 75% the rate observed for the ruthenium analogue, but with significantly enhanced catalyst lifetime. Acceptorless cyclodecane dehydrogenation under reflux conditions gave 125 turnovers of cyclodecenes in one hour. Spectroscopic evidence on the nature of the catalyst resting state and catalyst thermal and air stability is presented.