One-pot Synthesis for Osmium (II) Azavinylidene-carbyne and Azavinylidene-alkenylcarbyne Complexes Starting from an Osmium (II) Hydride-azavinylidene Compound

Autores: Ricardo Castarlenas, Miguel A. Esteruelas y Enrique Oñate Ref. revista: Organometallics, 20, 3283-3292, (2001)

Treatment at room temperature of the complex OsHCl2(dNdCMe2)(PiPr3)2 (1) with Ag-
[CF3SO3] and the subsequent stirring of the resulting solution under an acetylene atmosphere
gives the azavinylidene-carbyne derivative [OsCl(dNdCMe2)(tCCH3)(PiPr3)2][CF3SO3] (2).
The related complexes [OsCl(dNdCMe2)(tCCH2R)(PiPr3)2][CF3SO3] (R ) Cy (3), (CH2)2-
CH3 (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(dNdCMe2)(dCdCHR)(PiPr3)2 (R ) H (5), Cy (6), (CH2)2CH3 (7)), as a result of the deprotonation of the â-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)-CHdCHCy}Cl(dNdCMe2)(PiPr3)2][CF3SO3] (8), where the Hâ 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(dCdCHCy)(NHdCMe2)(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(dNdCMe2)(tCCHdCMe2)(Pi-Pr3)2][CF3SO3] (10), which by deprotonation with MeLi yields the azavinylidene-alkenylvinylidene OsCl(dNdCMe2){dCdCHC(Me)dCH2}(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)-CHdCHC(Me)dCMe2}Cl(dNdCMe2)(PiPr3)2][CF3SO3] (12), which in solution at room temperature evolves into 10. The complexes [OsCl(dNdCMe2)(tCCHdCPhR)(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(dNdCMe2){dCdCHC(Ph)dCH2}-
(PiPr3)2 (15).