Acceptor Pincer Chemistry of Ruthenium: Catalytic Alkane Dehydrogenation by (^CF^₃PCP)Ru(cod)(H)

Abstract

The synthesis and reactivity of a series of Ru(II) complexes based on the strongly π-accepting pincer ligand 1,3-C6H3(CH2P(CF3)2)2 (CF3PCP) is reported. Thermolysis of [Ru(cod)(η3-2-methylallyl)2] with CF3PCPH under H2 affords a mixture of the three complexes (μ-CF3PCPH)Ru(H)(μ-H)(μ-η6,κ3-CF3PCP)Ru(H), [(CF3PCP)Ru(H)]2(μ-CF3PCPH)2, and (CF3PCP)Ru(cod)H, which were structurally characterized and individually prepared in moderate yields. (CF3PCP)Ru(cod)H reacts with (C2F5)2PCH2CH2P(C2F5)2 (dfepe) to give (CF3PCP)Ru(dfepe)H. (CF3PCP)Ru(cod)H is moderately active as an alkane dehydrogenation catalyst. Thermolysis in 1:1 mixtures of cyclooctane and tert-butylethylene at 150 and 200 °C resulted in initial rates of 180 and 1000 turnovers h–1 of cyclooctene, respectively. Acceptorless dehydrogenation of cyclooctane also occurs, with an initial rate of 14 turnovers h–1. The decrease of catalyst activity over time was found to be due to thermal catalyst decomposition rather than product inhibition by cyclooctene.