Transition metal ions bound to organic radicals have been recognized as important species in chemical and enzymatic catalysis. For example, in the catalytic cycle of extradiol catechol dioxygenases, M(II) (M = Fe, Mn, Co) semiquinonate motifs are proposed to be involved as key intermediates. However, synthetic compounds showing catechol dioxygenase reactivities are almost exclusively iron(III) catecholate, which is proposed to be in resonance with iron(II) semiquinonate. Meanwhile, well characterized cobalt and manganese model complexes showing extradiol or intradiol catechol dioxygenase reactivities are very limited.Given the ability of tris(thioether)borate (phenyltris((tert-butylthio)methyl)borate, PhTtt-Bu) to provide a tridentate coordination environment and relatively weak ligand field, we reasoned that the M(II) monoanionic radical resonance form maybe be favored over the M(III) dianion description when PhTtt-Bu is used as the ancillary ligand. Thus, PhTtt-Bu supported iron and cobalt complexes with a series of redox-active ligands were synthesized. While a-diiminato p-radical and 9,10-phenanthrenesemiquinone are the redox forms found in their corresponding iron(II) and/or cobalt(II) complexes, both semiquinone and catecholate characters seem to exist in CoII/III(3,5-di-tert-butyl-benzosemiquinone/catecholate) complex, whose electronic structure and magnetic properties are of interest. Furthermore, upon addition of O2 to CoII/III(3,5-di-tert-butyl-benzosemiquinone/catecholate) complex, intradiol catechol dioxygenase reactivity was observed based on the exact match of the 1H NMR and CI�MS sepctra.

Tris(thioether)borate supported iron and cobalt complexes with redox�active ligands

246th National Meeting (2013)

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