One-Pot Synthesis for Osmium(II) Azavinylidene−Carbyne and Azavinylidene−Alkenylcarbyne Complexes Starting from an Osmium(II) Hydride−Azavinylidene Compound

Abstract

Treatment at room temperature of the complex OsHCl2(NCMe2)(PiPr3)2 (1) with Ag[CF3SO3] and the subsequent stirring of the resulting solution under an acetylene atmosphere gives the azavinylidene−carbyne derivative [OsCl(NCMe2)(⋮CCH3)(PiPr3)2][CF3SO3] (2). The related complexes [OsCl(NCMe2)(⋮CCH2R)(PiPr3)2][CF3SO3] (R = Cy (3), (CH2)2CH3 (4)) have been prepared by reaction of 1 with Ag[CF3SO3] and cyclohexylacetylene or 1-pentyne. The structure of 2 in the solid state has been determined by an X-ray diffraction study. The geometry around the metal center could be described as a distorted trigonal bipyramid with apical phosphines and inequivalent angles within the Y-shaped equatorial plane. The azavinylidene coordinates in a bent fashion with an Os−N−C angle of 152.0(8)°. Complexes 2−4 react with MeLi to afford the five-coordinate azavinylidene−vinylidenes OsCl(NCMe2)(CCHR)(PiPr3)2 (R = H (5), Cy (6), (CH2)2CH3 (7)), as a result of the deprotonation of the β-CH2 group of the carbyne ligands in 2−4. The formation of 2−4 involves azavinylidene−alkenyl and imine−vinylidene intermediates. In agreement with this, it is also reported that, at −25 °C, the addition of cyclohexylacetylene to the solution resulting from the treatment of 1 with Ag[CF3SO3] affords [Os{(E)-CHCHCy}Cl(NCMe2)(PiPr3)2][CF3SO3] (8), where the Hβ atom of the alkenyl ligand interacts with the osmium atom to form an agostic bond. At −30 °C, the addition of NaCl to tetrahydrofuran solutions of 8 gives OsCl2(CCHCy)(NHCMe2)(PiPr3)2 (9), which evolves into 6 in solution at room temperature. Complex 1 also reacts with Ag[CF3SO3] and 2-methyl-1-buten-3-yne. The reaction leads to the azavinylidene−alkenylcarbyne [OsCl(NCMe2)(⋮CCHCMe2)(PiPr3)2][CF3SO3] (10), which by deprotonation with MeLi yields the azavinylidene−alkenylvinylidene OsCl(NCMe2){CCHC(Me)CH2}(PiPr3)2 (11). The formation of 10 proceeds similarly to those of 2−4. Thus, it has been observed that, at −25 °C, the addition of 2-methyl-1-buten-3-yne to the solution resulting from the treatment of 1 with Ag[CF3SO3] gives [Os{(E)-CHCHC(Me)CMe2}Cl(NCMe2)(PiPr3)2][CF3SO3] (12), which in solution at room temperature evolves into 10. The complexes [OsCl(NCMe2)(⋮CCHCPhR)(PiPr3)2][CF3SO3] (R = H (13), CH3 (14), Ph (15)) have been prepared by reaction of 1 with Ag[CF3SO3] and 1-phenyl-2-propyn-1-ol, 2-phenyl-3-butyn-2-ol, and 1,1-diphenyl-2-propyn-1-ol, respectively. The deprotonation of 14 with MeLi affords OsCl(NCMe2){CCHC(Ph)CH2}(PiPr3)2 (15).