Cβ(sp²)−H Bond Activation of α,β-Unsaturated Ketones Promoted by a Hydride-Elongated Dihydrogen Complex: Formation of Osmafuran Derivatives with Carbene, Carbyne, and NH-Tautomerized α-Substituted Pyridine Ligands

Complex [ OsH(η 2 -H 2 )(η 2 -CH 2 ═CH- o -C 5 H 4 N)(P i Pr 3 ) 2 ]BF 4 ( 1 ) reacts with methyl vinyl ketone in the absence of solvent to give [ OsH{CHCHC( O)CH 3 } 2 (P i Pr 3 ) 2 ]BF 4 ( 2 ), which can be described as two osmafurans joined by a common [OsH(P i Pr 3 ) 2 ] + fragment. The hydride ligand of 2 is fairly acidic. Thus, its treatment with sodium methoxide produces the deprotonation of the metal center to give Os{CHCHC( O)CH 3 } 2 (P i Pr 3 ) 2 ( 3 ). The reaction is not reversible; the protonation of 3 with HBF 4 ·OEt 2 leads to [ Os{CHCHC( O)CH 3 }{═CHCH 2 C(═ O)CH 3 }(P i Pr 3 ) 2 ]BF 4 ( 4 ), which in dichloromethane is unstable and evolves into [ Os{CHCHC( O)CH 3 }Cl{≡CCH═C(CH 3 )OH}(P i Pr 3 ) 2 ]BF 4 ( 5 ), containing an enolcarbyne ligand. In the solid state the anion of 5 is associated with the OH-hydrogen of the enol, by means of an H···F hydrogen bond. In dichloromethane the H···F hydrogen bond is broken and DFT calculations suggest that the OH-hydrogen atom forms an H···Cl hydrogen bond with the chlorine ligand. In the absence of solvent, complex 1 reacts with benzylideneacetophenone and benzylideneacetone to give [ Os{C(Ph)CHC( O)R}(η 2 -H 2 ){κ-C-[HNC 5 H 3 Et]}(P i Pr 3 ) 2 ]BF 4 (R = Ph ( 6 ), CH 3 ( 10 )), containing a NH-tautomerized 2-ethylpyridine ligand. Complexes [ Os{C(Ph)CHC( O)R}(η 2 -H 2 ){(CH 3 CN)}(P i Pr 3 ) 2 ]BF 4 (R = Ph ( 8 ), CH 3 ( 11 )) and [ Os{C 6 H 4 C( O)CH═CHPh}(η 2 -H 2 ){(CH 3 CN)}(P i Pr 3 ) 2 ]BF 4 ( 9 ) have been also isolated and characterized. The X-ray structures of 2, 5, and 6 are reported.