Coordination and Rupture of Methyl C(sp³)−H Bonds in Osmium−Polyhydride Complexes with δ Agostic Interaction

The hexahydride complex OsH 6 (P i Pr 3 ) 2 ( 1 ) reacts with 8-methylquinoline and 2-(dimethylamino)pyridine to give ( 2 ) and ( 3 ), 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 Δ H ⧧ = 18.9 ± 0.1 kcal·mol -1 and Δ S ⧧ = 3 ± 2 eu. Treatment of 2 with HBF 4 affords the hydride-elongated dihydrogen derivative ( 6 ), with the methyl group of the quinoline ligand coordinated in a η 3 -H 2 C fashion. The X-ray structure of 6 and the DFT optimization of the structure of the model cation [OsH(η 2 -H 2 )(CH 4 )(NH 3 )(PMe 3 ) 2 ] + prove that the methyl coordination in the δ agostic complex is similar to the methane coordination in the model compound. The reaction of 3 with HBF 4 leads to the cyclic carbene derivative ( 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 DFT calculations.