CATALYTIC SELECTIVE OXIDATION cyclooctene epoxidation

Gold-catalyzed oxidation of styrene was firstly reported by Choudhary and coworkers for Au NPs supported on metal oxides in the presence of an excess amount of radical initiator, t-butyl hydroperoxide (TBHP), to afford styrene oxide, while benzaldehyde and benzoic acid were formed in the presence of supports without Au NPs [199]. Subsequently, Hutchings and coworkers demonstrated the selective oxidation of cyclohexene over Au/C with a catalytic amount of TBHP to yield cyclohexene oxide with a selectivity of 50% and cyclohexenone (26%) as a by-product [2]. Product selectivity was significantly changed by solvents. Cyclohexene oxide was obtained as a major product with a selectivity of 50% in 1,2,3,5-tetramethylbenzene while cyclohexenone and cyclohexenol were formed with selectivities of 35 and 25%, respectively, in toluene. A promoting effect of Bi addition to Au was also reported for the epoxidation of cyclooctene under solvent-free conditions. 

Work in this laboratory has shown also that the Ru(poip)(0)2 complexes (porp = TMP, TDCPP, and TDCPP-Clg) are practically inactive for thermal 02-oxygenation of saturated hydrocarbons . Some activity data for 0.2 mM Ru solutions in benzene under air at 25°C for optimum substrates such as adamantane and triphenylmethane at 6 mM did show selective formation of 1-adamantol and trityl alcohol, respectively, but with turnover numbers of only -0.2 per day the maximum turnover realized was -15 after 40 days for the TDCPP system Nevertheless, this was a non-radical catalytic processes there was < 10% decomposition of the Ru(TDCPP)(0)2, and a genuine O-atom transfer process was envisaged . Quite remarkably (and as mentioned briefly in Section 3.3), at the much lower concentration of 0.05 mM, Ru(TDCPP-Clg)(0)2 in neat cyclooctene gave effective oxidation. For example, at 90°C under 1 atm O2, an essentially linear oxidation rate over 55 h gave about -70% conversion of the olefin with - 80% selectivity to the epoxide however, the system was completely bleached after - 20 h and, as the activity was completely inhibited by addition of the radical inhibitor BHT, the catalysis is operating by a radical process, but in any case the conversion corresponds to a turnover of 110,000 As in related Fe(porp) systems (Section 3.3, ref. 121), the Ru(porp) species are considered to be very effective catalysts for the decomposition of hydroperoxides (eqs. 

Both 0-atoms of Ru(TMP)(0)2 can be transferred to an olefin in a stoichiometric reaction to generate 2 moles of epoxide, and the species also catalyzes O -oxidation of olefins at ambient conditions in benzene with high selectivity and > 90% yields with norbomene the order of olefin reactivity is norbomene > c/s-p-methylstyrene > cyclooctene > (ra s-p-methylstyrenc, while epoxidation of cis- and /ra s-P-methylstyrene proceeds with retention of configuration . The suggested catalytic cycle shown in Figure 6 implies the key disproportionation of a Ru(IV)=0 intermediate to the Ru(VI)(0)2 and Ru(II) species (see also Section 2, eq. 16, and Section 3.1, eq. 25) ,... 

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