PHOTOCHEMICAL-SYNTHESIS OF TRINUCLEAR CLUSTER COMPOUNDS OF OSMIUM AND A GROUP-6 METAL ATOM - STRUCTURES OF (OC)5M[OS(CO)3(PME3)]2 (M = CR, W), (OC)5MO(OS(CO)3[P(OME)3])2/[(MEO)3P](OC)4OSMO(CO)5 (1/1), AND (OC)4W[(MU-H)OS(CO)3(PME3)]2

Clusters of the type (OC)5M[Os(CO)3(PR3)]2 (M = Cr, Mo, W; R = Me, OMe; R3 = (OCH2)3CMe) have been obtained (30-40% yield) by ultraviolet irradiation of (R3P)(OC)4OsM(CO)5 complexes in C6F6. The crystal structures of (OC)5Cr[Os(CO)3(PMe3)12 (1), (OC)5Mo{Os(CO)3[P(OMe)3]}2 (2) cocrystallized in a 1:1 ratio with [(MeO)3P](OC)4OsMo(CO)5, and (OC)5W[Os(CO)3(PMe3)]2 (3) have been determined by X-ray crystallography. Compound 1 crystallizes in the space group P1bar with a = 9.331 (1) angstrom, b = 12.013 (1) angstrom, c = 12.357 (1) angstrom, a = 87.36 (1)-degrees, beta = 85.94 (1)-degrees, gamma = 68.81 (1)-degrees, and Z = 2, R = 0.039 for 3660 reflections (I greater-than-or-equal-to 2.5sigma(I)) Compounds 2 and [(MeO)3P](OC)4OsMo(CO)5 cocrystallize in the space group P1bar with a = 8.788 (1) angstrom, b = 16.901 (2) angstrom, c = 18.456 (2) angstrom, a = 68.88 (1)-degrees, beta = 81.75 (1)-degrees, gamma = 77.01 (1)-degrees, and Z = 2; R = 0.037 for 2886 reflections. Compound 3 crystallizes in the space group P1bar with a = 9.540 (2) angstrom, b = 12.119 (2) angstrom, c = 12.278 (2) angstrom, a = 86.69 (1)-degrees, beta = 88.74 (1)-degrees, gamma = 67.56 (1)-degrees, and Z = 2; R = 0.028 for 3437 reflections. Each cluster consists of a triangular MOs2 unit with one phosphorus ligand trans to the Os-Os bond and the other cis to this bond; there are no bridging carbonyls. The radial carbonyls on the M(CO)5 unit adopt a staggered arrangement with respect to the carbonyls on the osmium atoms. The C-13 NMR spectra of the (OC)5M[Os(CO)3(PR3)]2 Clusters in solution at low temperature were consistent with the presence of two isomers, one with the structure found in the solid state, the other with both phosphorus ligands trans to the Os-Os bond. In all molecules the radial carbonyls of the M(CO)5 group were chemically equivalent, but not equivalent to the axial carbonyl This behavior is interpreted in terms of free rotation of the M(CO)5, group about an axis that passes through M and the midpoint of the Os-Os vector. The phosphite derivative [ax-(MeO)3P](OC)4W[Os(CO)3(PMe3)]2, (4) was prepared by heating 3 with P(OMe)3 in hexane at 50-degrees-C. The C-13 NMR spectrum of 4 indicated that, once again, the radial carbonyls on the W atom in each isomer were equivalent. The hydrido cluster (OC)4 W[mu-H)Os(CO)3(PMe3)]2 (5) was synthesized from 3 and hydrogen at 50-degrees-C; its structure was determined by X-ray crystallography. Compound 5 crystallizes in the space group Pbca with a = 15.339 (4) angstrom, b = 16.785 (3) angstrom, c = 20.633 (6) angstrom, and Z = 8; R = 0.055 for 1591 observed reflections. The structure consists of a triangular array of metal atoms (Os-W = 3.154 (2) and 3.156 (3) angstrom, Os-Os = 2.964 (3) angstrom) with each PMe3 ligand trans to the Os-Os bond. The spectroscopic evidence is consistent with a hydride ligand bridging each OsW vector. The C-13 NMR spectrum indicates that in solution 5 has the same structure as found in the solid state and the molecule is stereochemically rigid.