| Recent interest in strong metal support interactions (SMSI) and evidence for support participation in oxygenate-forming Fischer-Tropsch catalysis prompted our investigation of early/late heterobimetallic complexes, homogeneous models for such systems. Preliminary studies showed that the difunctional ligand, (hydroxymethyl)diphenylphosphine (HOCH{dollar}sb2{dollar}PPh{dollar}sb2{dollar}), could be used as an effective linking agent in the synthesis of heterobimetallic complexes. Inspection of molecular models suggested the ligand would hold metal centers at an appropriate distance for cooperative activation of small molecules. An X-ray crystal structure of Cp*Zr({dollar}mu{dollar}-OCH{dollar}sb2{dollar}Ph{dollar}sb2{dollar}P){dollar}sb3{dollar}NiCO confirmed this suggestion by revealing a non-bonded intermetallic distance of 4.049 A. A series of compounds containing rhodium or platinum and zirconium or tantalum, and having methyl groups on both metals, were also prepared.; Cooperative reactivity was found when the reaction of Cp*ZrMe(OCH{dollar}sb2{dollar}Ph{dollar}sb2{dollar}P){dollar}sb2{dollar} with 0.5 equivalents of ((OC){dollar}sb2{dollar}RhCl) {dollar}sb2{dollar} yielded the bridging acyl, Cp*Zr({dollar}mu{dollar}-Cl)({dollar}mu{dollar}-OCH{dollar}sb2{dollar}Ph{dollar}sb2{dollar}P){dollar}sb2(musp2:etasp2{dollar}-OC(CH{dollar}sb3{dollar}))RhCO, which upon treatment with HCl or MeI liberated the C{dollar}sb2{dollar}-oxygenate fragment as acetaldehyde or acetone, respectively. While attempting to probe earlier steps in oxygenate formation, novel Rh/Zr compounds bearing alkyl or hydride substituents were synthesized. An X-ray crystal structure of one of these complexes, formed by the reaction of Cp*ZrMe(OCH{dollar}sb2{dollar}Ph{dollar}sb2{dollar}P){dollar}sb2{dollar} and one equivalent of (Ph{dollar}sb3{dollar}P){dollar}sb3{dollar}RhMe, revealed that an oxidative addition of the Zr-Me moiety across the rhodium center had occurred, giving cis-Cp*Zr({dollar}mu{dollar}-OCH{dollar}sb2{dollar}Ph{dollar}sb2{dollar}P){dollar}sb2{dollar}RhMe{dollar}sb2{dollar}. The very short Rh-Zr distance (2.448 A) is indicative of extensive {dollar}pi{dollar}-character in the bonding. Various derivatives were prepared, and their small molecule reactivity was explored. |
