Iron(II)-catecholate complexes of a monoanionic facial <i style="">N₃</i> ligand: Structural and functional models of the extradiol cleaving catechol dioxygenases

Abstract

Two biomimetic iron(II)-catecholate complexes, [(Tp^Ph2)Fe^II(CatH)] (<b style="">1</b>) and [(Tp^Ph2)Fe^II(DBCH)] <b>(2)</b> (where Tp^Ph2 = hydrotris(3,5-diphenylpyrazole-1-yl)borate, CatH = monoanionic pyrocatecholate and DBCH = monoanionic 3,5-di-<i style="">tert</i>-butyl catecholate), have been isolated and characterized to study their reactivity towards dioxygen. The single-crystal X-ray structure of <b style="">(1)</b> reveals a high-spin iron(II) center ligated by the monoanionic facial <i style="">N</i><i style="">₃</i> ligand and a monoanionic catecholate, giving rise to a trigonal bipyramidal coordination geometry. Complex <b style="">(1)</b> represents the first structurally characterized five-coordinate iron(II)-catecholate complex with an asymmetric bidentate binding motif of monoanionic catecholate. While <b style="">(1)</b> reacts with dioxygen to form the corresponding iron(III)-catecholate, <b style="">(2)</b> reacts with dioxygen to give 75 % extradiol and 25 % intradiol cleavage products via an iron(III)-catecholate intermediate species. Complex <b style="">(2)</b> is a potential functional model of extradiol cleaving catechol dioxygenases.