OsH{sub 5}(PMe{sub 2}Ph){sub 3}{sup +}: Structure, reactivity, and its use as a catalyst precursor for olefin hydrogenation and hydroformylation
- Indiana Univ., Bloomington, IN (United States); and others
OsH{sub 5}L{sub 3}{sup +} (as its BF{sub 4}{sup {minus}} salt; L = PMe{sub 2}Ph) is characterized by neutron diffraction as a dodecahedral pentahydride. However, the H/H separations are as short as 1.49(4) {angstrom}. This cation exchanges OsH with D{sub 2} and is converted by CO to OsH(CO){sub 2}L{sub 3}{sup +}. This cation hydrogenated ethylene (<1 h) at 25 {degrees}C to generate cis mer-OsH(C{sub 2}H{sub 4}){sub 2}L{sub 3}{sup +}, which was characterized by variable-temperature {sup 31}P, {sup 1}H, and {sup 13}C NMR spectroscopy and X-ray diffraction. The orientation of the olefins in this compound is explained using extended Hueckel methods, as is the lack of a structural trans influence on Os-C bond lengths and the reversed kinetic trans effect. Studies with Os/D and C{sub 2}D{sub 4} labeling, as well as trapping of transients with CO and with 1,5-cyclooctadiene, serve to define a reaction mechanism for ethylene hydrogenation, and the pentahydride cation also hydrogenates cyclohexene. In spite of the mutual trans stereochemistry of hydride and ethylene in OsH-(CO)(C{sub 2}H{sub 4})L{sub 3}{sup +} and then more slowly to cis,mer-Os[C(O)Et](CO){sub 2}Lp{sub 3}{sup +}. A variety of isotopic labeling studies prove that the first of these reactions does not involve preequilibrium dissociation of CO, PMe{sub 2}Ph, or C{sub 2}H{sub 4}, nor does it involve bimolecular proton transfer to form the ethyl group. Intramolecular hydrogen migration to bring H cis to C{sub 2}H{sub 4} is consistent with all observations. The carbonyl ligands in OsH(CO){sub 2}L{sub 3}{sup +} are susceptible to nucleophilic attack by solvent in water, to effect the water gas shift reaction. In the presence of water and 1-hexene, Reppe hydroformylation (H{sub 2}O + 2CO + olefin {yields} aldehyde + CO{sub 2}) is catalyzed by OsH(CO)(L{prime})L{sub 3}{sup +} (L{prime} = CO or C{sub 2}H{sub 4}) and by Os(Et)(CO){sub 2}L{sub 3}{sup +}.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 420980
- Journal Information:
- Inorganic Chemistry, Vol. 33, Issue 22; Other Information: PBD: 26 Oct 1994
- Country of Publication:
- United States
- Language:
- English
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