Formation of Imine-vinylidene-osmium(II) Derivatives by Hydrogen Transfer from Alkenyl Ligands to Azavinylidene Groups in Alkenyl-Azavinylidene-Osmium(IV) Complexes

Autores: Ricardo Castarlenas, Miguel A. Esteruelas y Enrique Oñate Ref. revista: Organometallics, 19, 5454-5463, (2000)

Treatment at room temperature of the hydride-azavinylidene complexes OsHCl2(dNdCR2)-(PiPr3)2 [CR2 ) CMe2 (1), C(CH2)4CH2 (2)] with Ag[CF3SO3] and the subsequent addition at -25 °C of phenylacetylene to the resulting solutions affords the alkenyl-azavinylidene derivatives [Os{(E)-CHdCHPh}Cl(dNdCR2)(PiPr3)2][CF3SO3] [CR2 ) CMe2 (3), C(CH2)4CH2(4)], where the Hâ atoms of the alkenyl ligands interact with the osmium atoms to form agostic bonds. The addition at -30 °C 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)-CHdCHPh}Cl2(dNdCR2)(PiPr3)2 [CR2 ) CMe2(5), C(CH2)4CH2 (6)]. In dichloromethane at room temperature complexes 5 and 6 evolve into the imine-vinylidene derivatives OsCl2(dCdCHPh)(NHdCR2)(PiPr3)2 [CR2 ) CMe2 (7), C(CH2)4CH2) (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 ClââââH separation of 2.366 Å and a Cl-Os-N angle of 77.34(18)°, largely deviated from the ideal value of 90°. Complexes 3 and 4 also react with water at -20 °C to give the cationic imine-vinylidene derivatives [OsCl(dCdCHPh)(NHdCR2)(H2O)(PiPr3)2][CF3SO3] [CR2 ) CMe2 (9), C(CH2)4CH2 (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-HâââO hydrogen bond is manifested by an OâââH separation of 2.36 Å and a N-Os-O angle of 78.3(2)°. The formation of 9 and 10 proceeds via the cationic six-coordinate alkenyl-azavinylidene-osmium(IV) intermediates [Os{(E)-CHdCHPh}Cl(dNdCR2 (H2O)(PiPr3)2][CF3SO3] [CR2 ) CMe2 (11), C- (CH2)4CH2 (12)], which have been characterized in solution at -90 °C by 1H and 31P{1H} NMR spectroscopy. Complexes 3 and 4 react with acetonitrile to give [OsCl(dCdCHPh)-(NHdCR2)(CH3CN (PiPr3)2][CF3SO3] [CR2 ) CMe2 (13), C(CH2)4CH2 (14)] via the intermediates [Os{(E)-CHdCHPh}Cl(dNdCR2)(CH3CN)(PiPr3)2[CF3SO3] [CR2 ) CMe2 (15), C-(CH2)4CH2 (16)].