METHYLENE CHAIN-LENGTH AND COORDINATION GEOMETRY IN TRIOSMIUM CLUSTERS CONTAINING DIPHOSPHINE LIGANDS - X-RAY CRYSTAL-STRUCTURES OF [OS-3(CO)(10)(MU-PH(2)P(CH2)(N)PPH(2))] (N=4 OR 5) AND [OS-3(CO)(8)(MU-PH(2)PCH(2)PPH(2))(2)]

The bis-acetonitrile compounds [Os-3(CO)(10)(MeCN)(2)] and the butadie ne compound [Os-3(CO)(10)(eta(4)-cis-C4H6)] react with dppp {dppp = Ph (2)P(CH2)(5)PPh(2)} to give only [Os-3(CO)(10)(mu-dppp)] (1). Protonat ion of 1 with trifluoroacetic acid leads to [(mu-H)Os-3(CO)(10)(mu-dpp p)](+) (2) with the hydride bridging the same osmium atoms as the dppp . The bridging dppp compound [Os-3(CO)(10)(mu-dppp)] (1) reacts with d ppp at 110 degrees C to give [Os-3(CO)(9)(eta(1)-dppp)(mu-dppp)] (4) w hereas [Os-3(CO)(10)(mu-dppm)] under the same conditions reacts with d ppm (dppm = Ph(2)PCH(2)PPh(2)) to give [Os-3(CO)(8)(mu-dppm)(2)] (5). Protonation of 5 with trifluoroacetic acid gives [(mu-H)Os-3(CO)(8)(mu -dppm)(2)](+) (6) with the hydride bridging the unsubstituted Os - Os edge. The monoacetonitrile compounds [Os-3(CO)(11)(MeCN)] reacts with dppp at 0 degrees C to give two compounds: [Os-3(CO)(11)(eta(1)-dppp)] (7) containing one coordinated and one free phosphorus atom and [{Os- 3(CO)(11)}(2)(mu-dppp)] (8) with one dppp ligand bridging two Os-3(CO) (11) moieties. Solid-state structures for 1, 5 and the previously repo rted cluster [Os-3(CO)(10)(mu-dppb)] (3) {dppb = Ph(2)P(CH2)(4)PPh(2)} are reported. Compound 1 crystallizes in the space group P2(1)2(1)2(1 ) with unit cell parameters a = 11.770(2) Angstrom, b = 16.957(3) Angs trom, c = 21.681(5) Angstrom, V = 4327(2) Angstrom(3) and Z = 4. Least -squares refinement of 6118 reflections gave a final agreement factor of R = 0.077 (R(w) = 0.087). Compound 3 crystallizes in the space grou p P2(1)/c with unit cell parameters a = 12.361(2) Angstrom, b = 16.804 (2) Angstrom, c = 20.935(2) Angstrom, beta = 116.66(1)degrees, V = 388 6(2) Angstrom(3) and Z = 4. Least-squares refinement of 2284 reflectio ns gave a final agreement factor of R = 0.028 (R(w) = 0.032). Compound 5 crystallizes in the space group Pca2(1) with unit cell parameters a = 21.398(3) Angstrom, b = 15.684(4) Angstrom, c = 18.219(4) Angstrom, V = 6115(4) Angstrom(3) and Z = 4. Least-squares refinement of 5376 r eflections gave a final agreement factor of R = 0.060 (R(w) = 0.062).