Octahedral [TpRu(PMe3)(2)OR](n+) complexes (Tp = hydridotris(pyrazolyl) borate; R = H or Ph; n=0 or 1): Reactions at Ru(II) and Ru(III) oxidation states with substrates that possess carbon-hydrogen bonds

摘要

The Ru(II) complexes TpRu(PMe3)(2)OR (R) H or Ph) react with excess phenylacetylene at elevated temperatures to produce the phenylacetylide complex TpRu(PMe3)(2)(C CPh). Kinetic studies indicate that the reaction of TpRu(PMe3)(2)OH and phenylacetylene likely proceeds through a pathway that involves TpRu(PMe3)(2)OTf as a catalyst. The reaction of TpRu(PMe3)(2)OH with 1,4-cyclohexadiene at elevated temperature forms benzene and TpRu(PMe3)(2)H, while TpRu(PMe3)(2)OPh does not react with 1,4-cyclohexadiene even after 20 days at 85 degrees C. The paramagnetic Ru(III) complex [TpRu(PMe3)(2)OH][OTf] is formed upon single-electron oxidation of TpRu(PMe3)(2)OH with AgOTf. Reactivity studies suggest that [TpRu( PMe3)(2)OH][OTf] initiates reactions, including hydrogen atom abstraction, with C-H bonds that have bond dissociation energy < 80 kcal/mol. Experimentally, the O-H bond strength of the Ru(II) cation [TpRu(PMe3)(2)(OH2)][OTf] is estimated to be between 82 and 85 kcal/mol, while computational studies yield a BDE of 84 kcal/ mol, which are in reasonable agreement with the observed reactivity of [TpRu( PMe3)(2)OH](+).