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

Abstract

The hexahydride complex OsH6(PiPr3)2 (1) reacts with 8-methylquinoline and 2-(dimethylamino)pyridine to give OsH3(CH2C9H6N)(PiPr3)2 (2) and OsH3{CH2N(CH3)-o-C5H4N}(PiPr3)2 (3), respectively, as a result of the release of two hydrogen molecules of 1 and the C(sp3)-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 ¢Hq ) 18.9 ( 0.1 kcalâmol-1 and ¢Sq ) 3 ( 2 eu. Treatment of 2 with HBF4 affords the hydride-elongated dihydrogen derivative [OsH(è2-H2)(CH3C9H6N)(PiPr3)2]BF4 (6), with the methyl group of the quinoline ligand coordinated in a è3-H2C fashion. The X-ray structure of 6 and the DFT optimization of the structure of the model cation [OsH(è2-H2)(CH4)(NH3)(PMe3)2]+ prove that the methyl coordination in the ä agostic complex is similar to the methane coordination in the model compound. The reaction of 3 with HBF4 leads to the cyclic carbene derivative [OsH3{dCHN(CH3)-o-C5H4N}(PiPr3)2]BF4 (7), as a result of the release of a hydrogen molecule and a C(sp3)-H bond activation on the methylene group of 3. The formation of 2, 3, 6, and 7 has been analyzed by DFT calculations.