Formation of imine-vinylidene-osmium(II) derivatives by hydrogen transfer from alkenyl ligands to azavinylidene groups in alkenyl-azavinylidene-osmium(IV) complexes

Treatment at room temperature of the hydride-azavinylidene complexes OsHCl2(=N=CR2)((PPr3)-Pr-i)(2) [CR2 = CMe2 (1), C(CH2)(4)CH2 (2)] with Ag[CF3SO3] and the subsequent addition at -25 degreesC of phenylacetylene to the resulting solutions affords the alkenyl-azavinylidene derivatives [Os{(E)-CH=CHPh}Cl(=N=CR2)((PPr3)-Pr-i)(2)][CF3SO3] [CR2 = CMe2 (3), C(CH2)(4)CH2 (4)], where the H-beta atoms of the alkenyl ligands interact with the osmium atoms to form agostic bonds. The addition at -30 degreesC of NaCl to tetrahydrofuran solutions of 3 and 4 produces the split of the agostic interactions and the formation of the neutral six-coordinate alkenyl-azavinylidene compounds Os{(E)-CH=CHPh}Cl-2(=N=CR2)((PPr3)-Pr-i)(2) [CR2 = CMe2 (5), C(CH2)(4)CH2 (6)]. In dichloromethane at room temperature complexes 5 and 6 evolve into the imine-vinylidene derivatives OsCl2(=C=CHPh)(NH=CR2)((PPr3)-Pr-i)(2) [CR2 = CMe2 (7), C(CH2)(4)CH2) (8)], as a result of the hydrogen transfer from the styryl ligands to the azavinylidene groups. The structure of 7 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 octahedron with the imine group disposed trans to a chlorine atom and cis to the other one. The N-H hydrogen atom of the imine interacts with the latter to form an intramolecular N-H ... Cl hydrogen bond, which is manifested by a short Cl ... H separation of 2.366 Angstrom and a Cl-Os-N angle of 77.34(18)degrees, largely deviated from the ideal value of 90 degrees. Complexes 3 and 4 also react with water at -20 DC to give the cationic imine-vinylidene derivatives [OsCl(=C=CHPh)(NH=CR2)(H2O)((PPr3)-Pr-i)(2)][CF3SO3] [CR2 = CMe2 (9), C(CH2)(4)CH2 (10)]. The structure of 9 in the solid state has been also determined by an X-ray diffraction study. The geometry around the metal center is octahedral with the imine group disposed trans to chlorine atom and cis to the water molecule. In this case the N-H hydrogen atom of the imine interacts with the oxygen atom of water molecule. The N-H ... O hydrogen bond is manifested by an O H separation of 2.36 Angstrom and a N-Os-O angle of 78.3(2)degrees. The formation of 9 and 10 proceeds via the cationic six-coordinate alkenyl-azavinylidene-osmium(IV) intermediates [Os{(E)-CH=CHPh}Cl(=N=CR2)(H2O)((PPr3)-Pr-i)(2)][CF3SO3] [CR2 = CMe2 (11), C(CH2)(4)CH2 (12)], which have been characterized in solution at -90 degreesC by H-1 and P-31{H-1} NMR spectroscopy. Complexes 3 and 4 react with acetonitrile to give [OsCl(=C=CHPh)-(NH= CR2)(CH3CN)((PPr3)-Pr-i)(2)][CF3SO3] [CR2 = CMe2 (13), C(CH2)(4)CH2 (14)] via the intermediates [Os{(E)-CH=CHPh}Cl(=N=CR2)(CH3CN)((PPr3)-Pr-i)(2)[CF3SO3] [CR2 = CMe2 (15), C-(CH2)(4)CH2 (16)].