SYNTHESES, SPECTROSCOPIC CHARACTERIZATIONS, AND X-RAY STRUCTURES OF NEW OS(ETA(2)-H-2) COMPOUNDS CONTAINING AZOLE LIGANDS

The dihydrido-dichloro complex OsH2Cl2(P-i-Pr3)2 (1) reacts with 2,2'-biimidazole (H2bim) to give the dihydrogen derivative [OsCl(eta2-H-2)(H2bim)(P-i-Pr3)2]Cl (2). The molecular structure of 2 has been determined by X-ray investigation. 2 crystallizes with a dichloromethane molecule in the triclinic space group P1BAR with a = 12.133(1) angstrom, b = 16.034(1) angstrom, c = 18.321(1) angstrom, alpha = 105.10(1)degrees, beta = 90.01(1)degrees, gamma = 93.87(1)degrees, and Z = 4. The coordination geometry around the osmium center can be rationalized as a distorted octahedron with the two phosphine ligands disposed mutually trans. The remaining coordination sites of the octahedron are occupied by the dihydrogen ligand, the chloride atom, and by two nitrogen atoms of the chelate 2,2-biimidazole ligand. One of the two acidic NH groups of the 2,2'-biimidazole ligand of 2 can be deprotonated by NaBH4 to give [OsCl(eta2-H-2)(Hbim)(P-i-Pr3)2] (3). Similarly the 2,2'-biimidazole ligand of 2 is deprotonated by dimers of the type [M(mu-OMe)(diolefin)]2 to form the heterobimetallic compounds [(P-i-Pr3)2(eta2-H-2)ClOs(mu-Hbim)RhCl(COD)] (COD = 1,5-cyclooctadiene, 4), [(P-i-Pr3)2 (eta2-H-2)ClOs(mu-Hbim)IrCl(COD)] (5), and [(P-i-Pr3)2(eta2-H-2)ClOs(mu-Hbim)IrCl(TFB)] (TFB = tetrafluorobenzobarrelene, 6). The addition of pyrazole to 1 leads to the complex trans-dichloro-[OsCl2(eta2-H-2)-(Hpz)(P-i-Pr3)2] (7), which is transformed into its isomer cis-dichloro-[OsCl2(eta2-H-2)(Hpz)(P-i-Pr3)2] (8) by stirring in hexane at 60-degrees-C. The molecular structure of 8 has also been determinated. 8 crystallizes with a pyrazole molecule in the monoclinic space group C2/c (No. 15) with a = 21.575(3) angstrom, b = 8.743(1) angstrom, c = 31.341(9) angstrom, beta = 90.98(2)degrees, and Z = 8. The coordination geometry around the osmium center could be described as based on a distorted octahedron with the two phosphine ligands occuping the apical positions. The equatorial plane is formed by the dihydrogen and the pyrazole ligands mutually cis-disposed and the two chloride atoms are also cis-disposed.