Synthesis, spectroscopic characterization, and reactivity of the unusual five-coordinate hydrido-vinylidene complex OsHCl(C=CHPh) (PiPr(3))(2): Precursor for dioxygen activation

The hydrido-carbyne complex OsHCl2(CCH(2)Ph)(PiPr(3))(2) (1) reacts with sodium methoxide in 1:1 molar ratio to give the five-coordinate hydrido-vinylidene OsHCl(C=CHPh)(PiPr(3))(2) (2), which affords [OsHCl(CCH(2)Ph)(H2O)(PiPr(3))(2)]BF4 (3) by reaction with HBF4 . H2O. The spectroscopic data obtained for 2 indicate that in solution, it is a mixture of two conformers in equilibrium. The thermodynamic magnitudes involved in the equilibrium as well as the activation parameters for the conversion between them were determined by H-1 NMR spectroscopy in toluene-d(8). The values obtained were Delta H degrees = -0.7 (+/-0.1) kcal mol(-1), Delta S degrees = -2.3 (+/-0.6) cal K-1 mol(-1), Delta H-double dagger = 11.0 (+/-0.2) kcal mol(-1) and Delta S-double dagger = 3.2 (+/-0.6) cal K-1 mol(-1). room temperature under argon, complex 2 is stable in the solid state and in solution. However in the presence of air, it activates molecular oxygen to give the dioxo-styryl compound OsCl{(E)-CH=CHPh}(O)(2)(PiPr(3))(2) (4), which has been characterized by X-ray diffraction analysis. The geometry around of the osmium atom can be described as a distorted octahedron with the two oxygen atoms occupying two relative trans positions (O(1)-Os-O(2) = 179.5(5)degrees). Complex 2 also reacts with trimethylphosphite, sodium acetylacetonato (acetylacetonato = acac), and sodium acetato to give the six-coordinate hydrido-vinylidene derivatives OsHCl(C=CHPh){(P(OMe)(3)}(PiPr(3))(2) (8), OSH(acac)(C=CHPh)(PiPr(3))(2) (9), and OsH(eta(2)-O2CCH3)(C=CHPh)(PiPr(3))(2) (10), respectively. Complex 10 can also be prepared by treatment of OsH3(eta(2)-O2CCH3)(PiPr(3))(2) (11) with phenylacetylene. Similarly, the reactions of 11 with 1,1-diphenyl-2-propyn-1-ol and 1-ethynyl-1-cyclohexanol lead to OsH(eta(2)-O2CCH3)-{C=CHC(oH)Ph(2)}(PiPr(3))(2) (12) and OsH(eta(2)-O2CCH3){C=CHC=CH(CH2)(3)CH2}(PiPr(3))(2) (13), respectively.