OXIDATION REACTIONS OF A MACROCYCLIC DINUCLEAR COPPER(I) DIOXYGEN COMPLEX AND A DINUCLEAR COPPER(II) COMPLEX

Recently a solution phase copper(I) dinuclear complex of the ligand 11 1,14]-octacosa-1(26),2,9,11,13,15,22,24-octaene, (FD)2(DIEN)2 (1), and its dioxygen adduct were spectroscopically characterized. In this rep ort, the use of the dinuclear complex in performing oxidation reaction s with hydroquinones, phenols, catechols, ascorbic acid, and 3,4-dimet hylaniline in a 3:1 mixture of methanol and acetonitrile is described. It has been determined that the copper(I) dioxygen complex of (FD) 2( DIEN)2 (3) catalytically converts hydroquinones to the corresponding b enzoquinones, ascorbic acid to dehydroascorbic acid, and phenols to th eir 1,4-benzoquinones and diphenoquinones, in the presence of excess d ioxygen. Turnover numbers range between 5 and 20 h-1. Under the same c onditions 4-tert-butylcatechol (4-TBC) was transformed to the gamma-la ctone of the corresponding muconic acid ester, 3,5-di-tert-butylcatech ol (3,5-DTBC) was oxidized to the corresponding 1,2-benzoquinone, and 3,4-dimethylaniline (3,4-DMA) was converted to 3,4-nitrosobenzene, all with turnover numbers of less than 1. These reactions were found to o ccur under stoichiometric conditions as well. Hydroquinones, phenols a nd ascorbic acid, but not catechols and 3,4-DMA, were also found to be oxidized, under stoichiometric conditions, by a dinuclear copper(II) complex 5, prepared from the 2:1 stoichiometric reaction between CuCl2 and 1 in methanol. The rates for the stoichiometric oxidations were d etermined to be 5 to 100 times greater for copper(I)-dioxygen oxidatio ns than for corresponding copper(II) oxidations. On the basis of these observations, a catalytic scheme based on the copper(I) complex as th e initial active species is proposed. The following steps are suggeste d: (i) formation of a dinuclear copper(I)-dioxygen adduct, (ii) oxidat ion of the substrate by the dioxygen adduct with simultaneous formatio n of a Cu(II) dinuclear complex, and (iii) oxidation of the substrate by the copper(II) complex to produce a copper(I) dinuclear complex and the oxidation product of the substrate.