CHEMICAL MECHANISM OF DIOXYGEN ACTIVATION BY MANGANESE(III) SCHIFF-BASE COMPOUND IN THE PRESENCE OF ALIPHATIC-ALDEHYDES

The manganese(III) complexes with tetradentate Schiff base [H-2(L)] de rived from salicylaldehyde and 2-amino-1-benzylamine [abbreviated as H -2(salabza)], ethylenedimaine and 2-hydroxybenzophenone [H-2(7-Phe-sal en)], ethylenediamine and 2-hydroxyacetophenone [H-2(7-Me-salen)] show ed much higher activity for degradation of tetraphenylcyclopentadienon e(TCPN) the singlet oxygen ((1) Delta(g)) scavenger, in the presence o f cyclohexanecarboxaldehyde than those of the compounds with H-2(salen ) and H-2(salphen), which are derived from salicyaldehyde and ethylene diamine, and o-phenylenediamine, respectively. X-ray crystal structura l determinations of the former three compounds and electrochemical dat a of all the compounds have given strong support for the conclusion th at the active species for degradation of TCPN is an acylperoxo Mn-III species coordinated by an aliphatic peracid chelate, which should be d erived from aliphatic aldehyde and dioxygen, where the geometry of the tetradentate Schiff base around the Mn-III ion is of cis-beta-configu ration. Under the same experimental conditions, the corresponding iron (III) compounds exhibited negligible activity towards the activation o f the dioxygen molecule. This was explained in terms of the difference in electronic structures between the two metal ions. (C) 1997 Elsevie r Science Ltd.