KINETIC-STUDIES OF REACTIONS OF DIOXYGEN WITH CARBOXYLATE-BRIDGED DIIRON(II) COMPLEXES LEADING TO THE FORMATION OF (MU-OXO)DIIRON(III) COMPLEXES

Stopped-flow kinetic studies of the reactions of [Fe-2(BIPhMe)(2)(O2CH )(4)] (1a), where BIPhMe = 2,2'-bis(1-methylimidazolyl)phenylmethoxyme thane, and [Fe-2(OH)(Me(3)TACN)(2)(OAc)(2)](+) (2a), where TACN = 1,4, 7-trimethyl-1,4,7-triazacyclononane, with O-2 are presented. In CHCl3 both reactions are first-order in [O-2] and secondorder in diiron(II) complex concentration. Mechanisms consistent with the kinetic data are proposed. The main feature of these schemes is a bimolecular pathway involving a tetranuclear (mu(4)-peroxo)diiron(II)diiron(III) species i n the transition state. Evidence for carboxylate shifts in the oxidati on mechanisms is presented, offering one possible way in which this cl ass of structural equilibria might control the chemistry at related no n-heme diiron centers in metalloproteins.