COOXIDATIVE EPOXIDATION OF CYCLOHEXENE WITH MOLECULAR-OXYGEN, ISOBUTYRALDEHYDE REDUCTANT, AND THE POLYOXOANION-SUPPORTED CATALYST PRECURSOR9)(4)N](5)NA-3[(1,5-COD)IR-CENTER-DOT-P2W15NB3O62] - THE IMPORTANCE OF KEY CONTROL EXPERIMENTS INCLUDING OMITTING THE CATALYST AND ADDING RADICAL-CHAIN INITIATORS

To reveal the underlying problems and misleading results that can be o btained from uninitiated O-2/aldehyde/olefin co-oxidative epoxidations that proceed by a radical-chain mechanism, a series of nearly identic al experiments were set up at the University of Tokyo and Colorado Sta te University. The main catalyst precursor studied is the oxidatively resistant, polyoxoanion-supported organometallic complex [(n-C4H9)(4)N ]Na-5(3)[(1,5-COD)Ir . P2W15Nb3O62], 1. Three other L(n)M . P2W15Nb3O6 2n- complexes were also examined [L(n)M=Re(CO)(3)(+), Ru(C6H6)(2+), an d Rh(1,5-COD)(+)], as well as the framework-incorporated cobalt(II) co mplex, [(n-C4H9)(4)N]H-4[(PW11CoO393-)-O-II]. Several types of importa nt but often omitted control reactions were also performed, again to e xpose the pitfalls in studies of O-2/aldehyde/olefin co-oxidative epox idations, specifically: (i) the control of leaving out the catalyst co mpletely, (ii) controls for O-2-mass-transfer limitations, (iii) contr ols examining a range of different solvents (CH3CN, CH2Cl2, ClCH2CH2Cl , and Cl2CHCHCl2), and (iv) controls comparing uninitiated versus deli berately peroxide-initiated reactions. The resultant reproducibilities , product conversions, selectivities, and yields are presented and dis cussed, as are stereochemical results using cis- and hans-stilbene. Se veral important insights are generated for the area of co-oxidative ep oxidations proceeding by a radical-chain mechanism, most notably that the catalyzed results are inferior to ROOH-initiated, uncatalyzed co-o xidative epoxidations examined under otherwise identical conditions.