Polyoxoanion-supported, atomically dispersed transition metals: The catalytic oxidation of cyclohexene with dioxygen by the catalyst precursors ((n-C sub 4 H sub 9 ) sub 4 N) sub 5 Na sub 3 ((1,5-COD)Irter dot P sub 2 W sub 15 Nb sub 3 O sub 62 ), ((n-C sub 4 H sub 9 ) sub 4 N) sub 5 Na sub 3 ((1,5-COD)Rhter dot P sub 2 W sub 15 Nb sub 3 O sub 62 ), and ((n-C sub 4 H sub 9 ) sub 4 N) sub 4. 5 Na sub 2. 5 ((C sub 6 H sub 6 )Ruter dot P sub 2 W sub 15 Nb sub 3 O sub 62 )

((n-C{sub 4}H{sub 9}){sub 4}N){sub 5}Na{sub 3}((1,5-COD)Ir{center dot}P{sub 2}W{sub 15}Nb{sub 3}O{sub 62}), 1, ((n-C{sub 4}H{sub 9}){sub 4}N){sub 5}Na{sub 3}((1,5-COD)Rh{center dot}P{sub 2}W{sub 15}Nb{sub 3}O{sub 62}), and ((n-C{sub 4}H{sub 9}){sub 4}N){sub 4.5}Na{sub 2.5}((C{sub 6}H{sub 6})Ru{center dot}P{sub 2}W{sub 15}Nb{sub 3}O{sub 62}) have been shown to catalyze the oxygenation of cyclohexene with molecular oxygen. The polyoxoanion-supported iridium (I) complex, 1, shows the highest activity of this group with a turnover frequency of 2.9 h{sup {minus}1} at 38{degree}C in CH{sub 2}Cl{sub 2} (540 total turnovers), which is 100-fold greater than its parent iridium compound, ((1,5-COD)IrCl){sub 2}. Additional experiments using H{sub 2}/O{sub 2} mixtures and H{sub 2}O{sub 2} are also discussed. The apparent rate law for the oxidation of cyclohexene by O{sub 2} by 1 is -d(cyclohexene)/dt = k{sub 2} obsd {center dot} (1){sup 1}(cyclohexene){sup 1}P(O{sub 2}){sup 1{yields}0}. These compounds constitute the first examples of oxygenation catalysis using molecular oxygen and a polyoxoanion-supported transition-metal precatalyst.