MU-3-ETA-2-ACYL AND MU-ALKYLIDENE COMPLEXES OF A MOLYBDENUM TRIOSMIUM CLUSTER - CRYSTAL-STRUCTURE OF CPMOOS3(CO)9(MU-H)(MU-O)(MU-CHCH2TOL)

Abstract

Initial decarbonylation of CpMoOs3(CO)11[mu3-eta2-C(O)CH2Tol] (4; Cp = eta5-C5H5, Tol = p-C6H4Me) with Me3No/MeCN followed by reaction with dihydrogen gives the dihydride complex CpMoOs3(CO)10(mu-H)2[mu3-eta2-C(O)CH2Tol] (5) in a quantitative yield. Thermolysis of 5 induces scission of the acyl C-O to afford the three isomeric hydrido-oxo-alkylidene compounds CpMoO3(CO)9(mu-H)(mu-O)(mu-CHCH2Tol) (6a-c). Complexes 6a,b are not chromatographically separable, and compound 6c is produced either by heating a mixture of 6a and 6b in toluene (100-degrees-C) or by treating with hydrochloric acid. Compounds 4, 5, and 6a-c have been isolated as crystalline solids and have been characterized by spectroscopic (infrared, mass, H-1 and C-13 NMR) data. The molecular structure of compound 6c has been determined by a single-crystal X-ray diffraction study. Complex 6c crystallizes in the orthorhombic space group Pmn2(1) with a = 12.438 (7) angstrom, b = 8.797 (2) angstrom, c = 11.846 (4)angstrom, V = 1296 (1) angstrom3, and D(calcd) = 2.87 g cm-3 for Z = 2 and molecular weight 1118.9. Diffraction data were collected on a CAD4 diffractometer, and the structure was refined to R(F) = 6.0% and R(W)(F) = 7.5% for 1236 data (Mo Kalpha radiation). The molecule is based upon a te MoOs3 core. Each osmium atom is coordinated to three terminal CO ligands, and the molybdenum atom is bonded to an eta5C5H5, ligand. The mu-oxo, mu-alkylidene, and mu-hydrido ligands bridge each edge of one of the Os-Os-Mo triangular faces. The mu-oxo and mu-alkylidene groups are disordered out of the crystallographic mirror plane which bisects the MoOs3 core. The mu-hydride ligand is believed to span the elongated Os-Os edge of the tetrahedron. The aryl moiety (CH2Tol) is disposed toward the mu-oxo ligand, which clearly indicates that 6c is formed from a mixture of 6a and 6b by an apparent rotation of the mu-alkylidene carbon.