REACTIVITY OF OSH4(CO)(PIPR3)2 TOWARD TERMINAL ALKYNES - SYNTHESIS AND REACTIONS OF THE ALKYNYL-DIHYDROGEN COMPLEXES OSH(C2R)(ETA-2-H2)(CO)(PIPR3)2 (R = PH, SIME3)

The tetrahychido OsH4(CO)(PiPr3)2 (1) reacts with the stoichiometric amount of phenylacetylene under hydrogen atmosphere to give OsH(C2Ph)(eta2-H-2)(CO)(PiPr3)2(2). After several hours, under hydrogen atmosphere, 2 is converted into OsH2(eta2-H2C=CHPh)(CO)(PiPr3)2 (4), which subsequent evolves to 1 and styrene. 4 and acetone are produced from the reaction of 2 with 2-propanol. The dihydrogen ligand of 2 is easily displaced by neutral ligands such as CO, P(OMe)3, and Hpz to give the complexes OsH(C2Ph)(CO)L(PiPr3)2 (5-7). The reaction of 2 with phenylacetylene affords OS(C2Ph)2(CO)(PiPr3)2 (8), which reacts with hydrogen to give 2 and styrene. The reaction of 8 with pyrazole gives rise to Os(C2Ph)2(CO)(Hpz)(PiPr3)2 (9). The complexes OsH(C2SiMe3)(eta2-H-2)(CO)(PiPr3)2 (10), OsH(C2SiMe3)(CO)L(PiPr3)2 (L = P(OMe)3 (11), Hpz (12)), Os(C2SiMe3)2(CO)(PiPr3)2 (13), and Os(C2SiMe3)2(CO)L(PiPr3)2 (L = P(OMe)3 (14), Hpz (15)) were prepared similarly to the related 2-9 starting from 1 and (trimethylsilyl)acetylene. The reaction of 1 with methylpropiolate gives Os(C2CO2Me)(CH=C-(H)C(OMe)=O)(CO)(PiPr3)2(16). The molecular structure of complex 16 has been determined. Crystals of 16 are orthorhombic, space group Pna2(1), with unit cell dimensions a = 14.9009 (6) angstrom, b = 14.6152 (5) angstrom, and c = 14.0339 (6) angstrom. The structure was solved and refined to the following R and Rw values: 0.022 and 0.022 on 4589 observed (F greater-than-or-equal-to 5.0s(F)) data. The molecular structure determination has confirmed the sigma-alkynyl coordination of a sigma-C=CCO2Me ligand, together with the reduction of a second alkyne molecule to give the corresponding vinylic ligand, which is bonded as a chelate group through the terminal vinylic carbon and the ketonic oxygen, generating a five-membered metallacycle ring. Two triisopropylphosphine molecules coordinated in relative trans positions and a carbonyl ligand, trans to the vinylic carbon, complete the osmium coordination sphere.