Oxygenated Cobalt Complexes with Simple Tetraazamacrocyclic Ligands

Abstract

Binuclear oxygenated cobalt complexes with 5,7,12,14-tetramethy I-1,4,8,II-tetraazacyclotetradeca-4,II -diene (Me₄14]dieneN₄) and 5,7,7,12,14,14-hexamethyl-1,4,8,11 -tetraazacyclotetradeca-4,11 -diene (Me₆14]dieneN₄) with axial ligands (NCO^?, NCS^?, NCSe^?, N^? ₃, OH^?, NO^? ₂, ON-C(CN)₂ ^?, Im) have been isolated and characterised by physical and chemical methods, including derivatography, electronic, IR and X-ray photoelectron spectroscopy, magnetic measurements and EPR. The electronic structure of the cobalt ion-dioxygen fragment conforms to the scheme Co(III)-O₂-Co(III). The coordinated dioxygen species is activated owing to the transfer of an appreciable electron density to it. Irreversible oxidation in aqueous solution is illustrated by μO₂{Co(Me₄14]dieneN₄)(H₂O)}₂](CIO₄)₄. Activation parameters for this process are E* = 54 ± 4 kJ mol^?1 and ΔS* = -140 ± 16 J mol K^?1. A possible mechanism is proposed.