Iron and cobalt complexes of 4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dioxime ligand: Synthesis, characterization and reactivity studies

Abstract

Two oximate bridged dinuclear complexes [Co\(^{\rm{II}}_{2}\)(HL)2](ClO4)2 (1) and [Fe\(^{\rm{II}}_{2}\)(HL)2](ClO4)2 (2), and a biomimetic iron(III)-catecholate complex [FeIII(HL)(DBC)] (3) of a dioxime ligand (H2L = 4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dioxime and DBCH2 = 3,5-di-tert-butylcatechol) were synthesized and characterized. X-ray single-crystal structures of both the dinuclear complexes exhibit an out-of-plane oximate bridge where the six-membered M2(NO)2 ring adopt a boat conformation with the metal ions in a five-coordinate distorted trigonal bipyramidal geometry. Complexes 1 and 2 react with dioxygen at ambient condition to form the corresponding hydroxo- or oxo-bridged dinuclear cobalt(III) or iron(III) complexes. On the other hand, the iron(III)-catecholate complex (3) activate dioxygen to undergo oxidative C–C bond cleavage of catechol. The selective formation of extradiol catechol cleavage products in the reaction of 3 with dioxygen mimics the functional aspect of extradiol-cleaving catechol dioxygenases. The flexibility of ligand backbone is proposed to control the dioxygen reactivity of metal complexes. Dinuclear cobalt(II) and iron(II) complexes of 4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dioxime ligand exhibit out-of-plane oximate bridge with the M2(NO)2 ring in a boat conformation. An iron(III)-catecholate complex of the dioxime ligand reacts with dioxygen to afford C–C bond cleavage products of catechol.