Dehydrogenation versus oxygenation in two-electron and four-electron reduction of dioxygen by 9-alkyl-10-methyl-9,10-dihydroacridines catalyzed by monomeric cobalt porphyrins and cofacial dicobalt porphyrins in the presence of perchloric acid

Dehydrogenation of 10-methyl-9,10-dihydroacridine (AcrH(2)) by dioxygen (O-2) proceeds accompanied by the two-electron and four-electron reduction of O-2 to produce H2O2, and H2O, which are effectively catalyzed by monomeric cobalt porphyrins and cofacial dicobalt porphyrins in the presence of perchloric acid (HCIO4) in acetonitrile (MeCN) and benzonitrile (PhCN), respectively. The cobalt porphyrin catalyzed two-electron reduction Of 02 also occurs efficiently by 9-alkyl-10-methyl-9,10-dihydroacridines; (AcrHR; R Me, Et, and CH2COOEt) to yield 9-alkyl-10-methylacridinium ion (AcrR(-)) and H2O2. In the case of R Bu' and CMe2COOMe, however, the catalytic two-election and four-electron reduction of O-2, by AcrHR results in oxygenation of the alkyl group of AcrHR rather than dehydrogenation to yield 10-methylacriclinium ion (AcrH(+)) and the oxygenated products of the alkyl groups. i.e.. the corresponding hydroperoxides (ROOH) and the alcohol (ROH), respectively. The Catalytic mechanisms of the dehydrogenation vs the oxygenation of AcrHR in the two-electron and four-electron reduction of O-2, Gatallyzed by monomeric cobalt porphyrins and cofacial dicobalt porphyrins, respectively, are discussed in relation to the C(9)-H or C(9)-C bond cleavage of AcrHR radical cations produced in the electron-transfer oxidation of AcrHR.