| The reaction of the tri-niobium substituted polyoxometalate ({dollar}(n{dollar}-{dollar}rm Csb4Hsb9)sb4Nrbracksb9Psb2Wsb{lcub}15{rcub}Nbsb3Osb{lcub}62{rcub}{dollar} with equimolar amounts of (M(1,5-COD)(CH{dollar}rmsb3CN)sb2rbrack BFsb4{dollar} (M = Ir, Rh; 1,5-COD = 1,5-cyclooctadiene) leads to the formation of the air-sensitive polyoxometalate-supported organometallic complexes ((1,5-COD)M{dollar}cdotrm Psb2Wsb{lcub}15{rcub}Nbsb3Osb{lcub}62{rcub}rbracksp{lcub}8-{rcub}{dollar} (M = Ir, Rh). These complexes were isolated as their mixed 5 ({dollar}(n{dollar}-{dollar}rm Csb4Hsb9)sb4Nrbracksp+/3Nasp+{dollar} salts, and have been characterized by {dollar}sp1{dollar}H, {dollar}sp{lcub}13{rcub}{dollar}C, {dollar}sp{lcub}31{rcub}{dollar}P, and {dollar}sp{lcub}183{rcub}{dollar}W NMR spectroscopy, IR, molecular-weight measurements and complete elemental analyses. Additional data in form of {dollar}sp{lcub}17{rcub}{dollar}O NMR studies for ((1,5-COD)Ir{dollar}cdotrm Psb2Wsb{lcub}15{rcub}Nbsb3Osb{lcub}62{rcub}rbracksp{lcub}8-{rcub}{dollar} demonstrates that iridium binds in overall average C{dollar}rmsb{lcub}3v{rcub}{dollar} (pseudo) symmetry to the "Nb{dollar}rmsb3Osb9sp{lcub}3-{rcub}{dollar}" minisurface in solution, where catalysis beginning with ((1,5-COD)Ir{dollar}cdotrm Psb2Wsb{lcub}15{rcub}Nbsb3Osb{lcub}62{rcub}rbracksp{lcub}8-{rcub}{dollar} as the precatalyst has previously been demonstrated.; The heteropolyoxoanion-supported complexes ({dollar}rm(Csb5Mesb5){lcub}Rhcdot P{rcub}sb2Wsb{lcub}15{rcub}Nbsb3Osb{lcub}62{rcub}rbracksp{lcub}7-{rcub}{dollar} and ({dollar}rm(Csb6Hsb6){lcub}Rucdot P{rcub}sb2Wsb{lcub}15{rcub}Nbsb3Osb{lcub}62{rcub}rbracksp{lcub}7-{rcub}{dollar} have been prepared by addition of {dollar}rm(Csb5Mesb5)Rhsp{lcub}2+{rcub}{dollar} or {dollar}rm(Csb6Hsb6)Rusp{lcub}2+{rcub},{dollar} respectively, to a solution of {dollar}rm Psb2Wsb{lcub}15{rcub}Nbsb3Osb{lcub}62{rcub}sp{lcub}9-{rcub}{dollar} in acetonitrile. Isolation of these complexes as homogeneous, yellow solids with mixed ({dollar}(n{dollar}-C{dollar}rmsb4Hsb9)sb4Nrbracksp+/Nasp+{dollar} cation composition was accomplished by repeated reprecipitation from acetonitrile with ethyl acetate. Molecular formulas were established by complete elemental analyses and molecular-weight measurements. The solution NMR data is in accord with {dollar}rm(Csb5Mesb5)Rhsp{lcub}2+{rcub}{dollar} and {dollar}rm(Csb6Hsb6)Rusp{lcub}2+{rcub}{dollar} being supported on three niobium-bridging oxygens on the "Nb{dollar}rmsb3Osb9sp{lcub}3-{rcub}{dollar}" surface of the heteropolyoxoanion. The structural characterization of ({dollar}rm(Csb5Mesb5){lcub}Rhcdot P{rcub}sb2Wsb{lcub}15{rcub}Nbsb3Osb{lcub}62{rcub}rbracksp{lcub}7-{rcub}{dollar} in the solid state was accomplished by a single crystal X-ray structural analysis: P6{dollar}sb3{dollar}/m, a = 20.544(5), b = 20.544(5), c = 34.648(6) A, Z = 2, R = 0.096 for 3023 observed independent reflections. This analysis, though limited by severe disorder, reveals that the Rh atom is on or very close to the crystal three-fold axis and bonded (Rh-ONb{dollar}sb2{dollar}, 2.06 A) to the three oxygen atoms each of which bridges a pair of Nb atoms in a cap of the Dawson unit. These results provide for the first solid-state structure of a Dawson-type heteropolyoxoanion supported-organometallic complex. |
