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 OsHCl 2 ( N CR 2 )(P i Pr 3 ) 2 [CR 2 = CMe 2 ( 1 ), ( 2 )] with Ag[CF 3 SO 3 ] and the subsequent addition at −25 °C of phenylacetylene to the resulting solutions affords the alkenyl−azavinylidene derivatives [Os{( E )-CH CHPh}Cl( N CR 2 )(P i Pr 3 ) 2 ][CF 3 SO 3 ] [CR 2 = CMe 2 ( 3 ), ( 4 )], where the H β 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 )-CH CHPh}Cl 2 ( N CR 2 )(P i Pr 3 ) 2 [CR 2 = CMe 2 ( 5 ), ( 6 )]. In dichloromethane at room temperature complexes 5 and 6 evolve into the imine−vinylidene derivatives OsCl 2 ( C CHPh)(NH CR 2 )(P i Pr 3 ) 2 [CR 2 = CMe 2 ( 7 ), ( 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 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( C CHPh)(NH CR 2 )(H 2 O)(P i Pr 3 ) 2 ][CF 3 SO 3 ] [CR 2 = CMe 2 ( 9 ), ( 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 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 )-CH CHPh}Cl( N CR 2 )(H 2 O)(P i Pr 3 ) 2 ][CF 3 SO 3 ] [CR 2 = CMe 2 ( 11 ), ( 12 )], which have been characterized in solution at −90 °C by 1 H and 31 P{ 1 H} NMR spectroscopy. Complexes 3 and 4 react with acetonitrile to give [OsCl( C CHPh)(NH CR 2 )(CH 3 CN)(P i Pr 3 ) 2 ][CF 3 SO 3 ] [CR 2 = CMe 2 ( 13 ), ( 14 )] via the intermediates [Os{( E )-CH CHPh}Cl( N CR 2 )(CH 3 CN)(P i Pr 3 ) 2 [CF 3 SO 3 ] [CR 2 = CMe 2 ( 15 ), ( 16 )].