Polyoxoanion-supported, atomically dispersed transition-metal precatalyst [(1,5-COD)Ir.cntdot.P2W15Nb3O62]8-: direct oxygen-17 NMR evidence for Ir-ONb2 bonding and for a C3v average symmetry, iridium-to-polyoxoanion support interaction

Selective enrichment with [sup 17]OH[sub 2] followed by [sup 17]O NMR allows observation of just the Nb[sub 3]O[sub 6] support site in the custom-designed polyoxoanion P[sub 2]W[sub 15]Nb[sub 3]O[sub 6][sup 9[minus]] and in the polyoxoanion-supported organometallic precatalyst [(n-C[sub 4]H[sub 9])[sub 4]N][sub 5]Na[sub 3][(1,5-COD)Ir-P[sub 2]W[sub 15]Nb[sub 3]O[sub 62]] (1) without interference from other [sup 17]O NMR resonances. The [sup 17]O NMR results provide direct evidence for Ir-ONb[sub 2] bonding between (1,5-COD)Ir[sub 1][sup +] (1,5-COD = 1,5-cyclooctadiene) and P[sub 2]W[sub 15]Nb[sub 3]O[sub 62][sup 9[minus]] in solution, where catalysis beginning with 1 has been demonstrated. The [sup 17]O NMR results are also definitive in demonstrating that [(1,5-COD)Ir[sup 1]][sup +] is bound in overall average C[sub 3[upsilon]] (pseudo) symmetry to the Nb[sub 3]O[sub 6] minisurface in 1 (pseudo due to the 2-fold axis in 1,5-COD and thus the local C[sub s] symmetry at Ir). 15 refs., 3 figs., 1 tab.