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(=N=CMe2)(PiPr3)2 (1) with Ag-[CF3SO3] and the subsequeny stirring of the resulting solution under an acetylene atmosphere gives the azavinylidene-carbyne derivative [OsCl(=N=CMe2)(≡CCH3)PiPr3] [CF3SO3] (2). The related complexes [OsCl(=N=CMe2)(≡CCH2R)(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(=N=CMe2)(=C=CHR)(PiPr3)2 (R = H (5), Cy (6), (CH2)2CH3 (7)), as result of the deprotonation of the βCH2 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)-CH=CHCy}Cl(=N=CMe2)(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(=C=CHCy)(NH=CMe2)Pi Pr3)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(=N=CMe2)(≡CCH=CMe2)(i- Pr3)2][CF3SO3] (10), which by deprotonation with MeLi yields the azavinylidene-alkenylvinylidene OsCl(=N=CMe2){=C=CHC(Me)=CH2=CH2}(Pi Pr3)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)-CH=CHC(Me)=CMe2}Cl(=N=CMe2)(PiPr3 )2][CF3SO3] (12), which in solution at room temperature evolves into 10. The complexes [OsCl(=N=CMe2)(≡CCH=CPhR)(Pi Pr3)2] [CF3-SO3] (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(=N=CMe2){=C=CHC(Ph)=CH2}-(Pi Pr3)2 (15).