CLUSTER SYNTHESIS .38. FORMATION OF HIGH-NUCLEARITY PLATINUM OSMIUM CLUSTER COMPLEXES - SYNTHESIS, STRUCTURAL CHARACTERIZATIONS, AND INTERRELATIONSHIPS OF PT4OS6(CO)22(COD), PT5OS6(CO)21(COD)2, PT4OS6(CO)19(COD)2, AND PT7OS6(CO)21(COD)2 (COD = CYCLOOCTA-1,5-DIENE)

Three new high-nuclearity platinum-osmium carbonyl cluster complexes Pt4Os6(CO)22(COD) (2), Pt5Os6(CO)21(COD)2 (3), and Pt4Os6(CO)19(COD)2 (4) were obtained in 17%, 13%, and 9% yields, respectively, from the pyrolysis Of Pt2Os3(CO)10(COD)2 (1) under a CO atmosphere at 128-degrees-C. Compounds 2-4 were characterized by IR, H-1 NMR, and single-crystal X-ray diffraction analyses. Compound 2 consists of two Pt3Os3 octahedra sharing a Pt3 triangular face. A Pt(COD) group caps one of the Os3 triangular faces. Compound 3 is structurally similar to compound 2 but has an additional Pt(COD) group capping one of the PtOs2 triangular faces. The cluster of compound 4 can be viewed as a meta-bicapped Pt2Os4 octahedron with an additional Pt(COD) group capping a PtOs2 triangle to one of the capping groups on the octahedron and a Pt(COD) group bridging the Pt-Pt edge of the octahedron. Compound 2 was converted to 4 in 65% yield, when it was irradiated in the presence of COD. When compound 2 was treated with 1 equiv of trimethylamine N-oxide and 2 equiv of Pt(COD)2, compound 3 and a new higher nuclearity platinum-osmium carbonyl complex Pt7Os6(CO)21(COD)2 (5; 8% yield) were obtained. Compound 5 was characterized by a single-crystal X-ray diffraction analysis. It was formed by the loss of one CO from 2 and the addition of three Pt atoms and one COD ligand. The structure consists of layers of metal atoms. A platinum-capped Os3 triangle sits next to a planar Pt4 layer, which in tum lies next to a planar five atom layer consisting of three osmium and two platinum atoms. Compound 2 was converted to the known compound Pt4Os6(CO)21(COD)(mu-H)2 (6) in good yield (79%) by reacting with trimethylamine N-oxide and hydrogen. Crystal data: for 2, space group P2(1)/n, a = 20.404 (6) angstrom, b = 9.607 (5) angstrom, c = 24.171 (8) angstrom, beta = 90.512 (3)-degrees, Z = 4, and R = 0.040 for 2847 reflections; for 3, space group P2,/m, a = 12.023 (8) angstrom, b = 16.010 (9) angstrom, c = 13.902 (7) angstrom, beta = 103.79 (5)-degrees, Z = 2, and R = 0.037 for 2428 reflections; for 4, space group C2/c, a = 45.67 (1) angstrom, b = 11.836 (4) angstrom, c = 17.444 (4) angstrom, beta = 99.04 (2)-degrees, and R = 0.034 for 3295 reflections; for 5, space group P2(1)/n, a = 21.061 (6) angstrom, b = 12.086 (3) angstrom, c = 21.348 (6) angstrom, beta = 92.06 (2)-degrees, and R = 0.039 for 3134 reflections.