Synthesis, characterization, and theoretical study of stable hydride-azavinylidene osmium(IV) complexes

摘要

The dihydride-dichloro complex OsH2Cl2(PiPr3)2 (1) reacts with cyclohexanone oxime in toluene under reflux to give after 12 h OsHCl2{N=C(CH2)4CH2}(P iPr3)2 (2), which can be also obtained by reaction of the oximate compound, OsH2Cl{κ-N,κ-O[ON=C(CH2)4CH 2]}(PiPr3)2 (3) with HCl. Complex OsHCl2{N=C(CH3)2}(PiPr 3)2 (4) has been similarly prepared by treatment of compound OsH2Cl{κ-N,κ-O[ON=C(CH3)2]}(P iPr3)2 (5) with HCl. When the reaction of 1 and cyclohexanone oxime, in toluene under reflux, was quenched after 1 h, a mixture of 1, 2, 3, and the trichloroazavinylidene OsCl3{N=C(CH2)4CH2}(P iPr3)2 (6) was obtained. The structures in the solid state of 2 and 6 have been determined by X-ray diffraction studies. In both cases, the geometry around the metal center can be described as a distorted octahedron with the phosphorus atoms of the phosphines occupying trans positions and the C=N group and the carbon atoms bonded to this group lying in a plane that is parallel to the Cl-Os-Cl plane. CCSD(T)//B3LYP calculations on the model complexes OsXCl2(N=CH2)(PH3)2 [X = H (2t), X = Cl (6t)] state that the above-mentioned conformation is 15.3 (2t) or 12.1 (6t) kcal mol-1 more stable than that with the azavinylidene ligand parallel to the P-Os-P plane. In solution the azavinylidene ligands of 2 and 4 rotate around the Os-N-C axis. The activation parameters of the process are ΔH = 14.4 ± 0.8 kcal mol-1 and ΔS = -1.1 ± 1.3 cal mol-1 K-1 for 2 and ΔH = 13.1 ± 0.8 kcal mol-1 and ΔS = 0.0 ± 2.8 cal mol-1 K-1 for 4. © 2000 American Chemical Society.