C(sp2)-H activation of RCH=E-py (E = CH, N) and RCH=CHC(O)R′ substrates promoted by a highly unsaturated osmium-monohydride complex

The 14-valence-electron monohydride OsH(SnPh2Cl)(PiPr(3))(2) (a), generated from OsH3(SnPh2Cl){eta(2) -CH2=C(CH3)(PPr2)-Pr-i}((PPr3)-Pr-i) (1), activates a C(sp(2))-H bond of 2-vinylpyridine, (E)-N(phenylmethylene)-2-pyridinamine, and alpha,beta-unsaturated ketones. The activation of 2-vinylpyridine affords the elongated dihydrogen (d(H-H) = 1.41 angstrom) derivative Os(SnPh2Cl)(NC5H4-o-CH= CH)(eta(2)-H-2)(PiPr(3))(2) (2) in equilibrium (Delta H degrees = -2.5 +/- 0.2 kcal mol(-1) and Delta S degrees = -14.8 +/- 1.0 cal mol(-1) K-1) with the tautomer OsH(NC5H4-o-CH=CH)(HSnPh2Cl)((PPr3)-Pr-i)(2) (3), where the stannane is bonded to the transition metal by an Os-H-Sn three-center bond (J(H-Sn) = 183 Hz). The activation of (E)-N-(phenylmethylene)-2-pyrid inamine gives rise to Os(SnPh2Cl)(NC5H4-o-NCPh)(eta(2)-H-2)((PPr3)-Pr-i)(2) (4; d(H-H) = 1.32 angstrom), whereas the treatment of 1 with methyl vinyl ketone and benzylidenacetone leads to Os(SnPh2Cl){C(R)CHC(O)CH3}(eta(2)-H-2)(eta(2)-H-2)(PiPr(3))(2) (R = H (5), Ph (6)), which show blocked rotation of the dihydrogen ligand (d(H-H) = 1.45 (5), d(H-H) = 1.42 (6) angstrom) on the NMR time scale (Delta H+ = 11.7 +/- 0.4 kcal mol(-1) and Delta S+ = -1 +/- 1 cal mol(-1) K-1 (5), Delta H+ = 10.8 +/- 0.5 kcal mol(-1) and Delta S+ = 0.4 +/- 1 cal mol(-1) K-1 (6)). Complex also reacts with benzylidenacetophenone. The reaction initially gives Os(SnPh2Cl){C(Ph) I CHC(O)Ph}(q(2)-H-2)(PiPr(3))(2) (7), which isomerizes into Os(SnPh2Cl){C6H4C(O)CH=CHPh}(eta(2)-H2)(PiPr3)2 (8), resulting from the o-CH activation of the PhCO aryl group. Complex 8 is other example of blocked rotation of the dihydrogen ligand (dH-H = 1.45 angstrom) on the NMR time scale (Delta H+ = 10.6 +/- 0.6 kcal mol(-1) and Delta S+ = -6.3 +/- 1.5 cal mol(-1) K-1). The structures of 2 and 5 have been determined by X-ray diffraction analysis.