THE POLYOXOANION-SUPPORTED, ATOMICALLY DISPERSED TRANSITION-METAL PRECATALYST [(1,5-COD)IR.P2W15NB3O62]8- - DIRECT O-17 NMR EVIDENCE FOR IR-ONB2 BONDING AND FOR A C3V AVERAGE SYMMETRY, IRIDIUM-TO-POLYOXOANION SUPPORT INTERACTION

Selective enrichment with (OH2)-O-17 followed by O-17 NMR allows observation of just the Nb3O6 support site in the custom-designed polyoxoanion P2W15Nb3O529- and in the polyoxoanion-supported organometallic precatalyst [(n-C4H9)4N]5Na3[(1,5-COD)Ir.P2W15Nb3O62] (1) without interference from other O-17 NMR resonances. The O-17 NMR results provide direct evidence for Ir-ONb2 bonding between [(1,5-COD)Ir(I)]+ (1,5-COD = 1,5-cyclooctadiene) and P2W15Nb3O629- in solution, where catalysis beginning with 1 has been demonstrated. The O-17 NMR results are also definitive in demonstrating that [(1,5-COD)Ir(I)]+ is bound in overall average C3v (pseudo) symmetry to the Nb3O6 minisurface in 1 (pseudo due to the 2-fold axis in 1,5- COD and thus the local C(s) symmetry at Ir).