Coordination and rupture of methyl C(sp3)-H bonds in osmium-polyhydride complexes with δ agostic interaction

The hexahydride complex OsH6((PPr3)-Pr-i)(2) (1) reacts with 8-methylquinoline and 2-(dimethylamino)pyridine to give [GRAPHICS] (2) and [GRAPHICS] respectively, as a result of the release of two hydrogen molecules of 1 and the C(sp(3))-H bond activation of a methyl group of the organic substrates. In solution the hydride ligands and the hydrogen atoms of the methylene group of 2 exchange their positions. The activation parameters for the process are Delta H-double dagger = 18.9 +/- 0.1 kcal.mol(-1) and Delta S-double dagger = 3 +/- 2 eu. Treatment of 2 with HBF4 affords the hydride-elongated dihydrogen derivative [GRAPHICS] (6), with the methyl group of the quinoline ligand coordinated in a eta(3)-H2C fashion. The X-ray structure of 6 and the DFT optimization of the structure of the model cation [OsH(eta(2)-H-2)(CH4)(NH3)(PMe3)(2)](+) prove that the methyl coordination in the delta agostic complex is similar to the methane coordination in the model compound. The reaction of 3 with HBF4 leads to the cyclic carbene derivative [GRAPHICS] (7), as a result of the release of a hydrogen molecule and a C(sp(3))-H bond activation on the methylene group of 3. The formation of 2, 3, 6, and 7 has been analyzed by DFF calculations.