ChemInform Abstract: Oxidative Addition of Quinones to Planar Cobalt(II) Dithiolato, Dithioacetylacetonato and Schiff-base Complexes.

ChemInform Abstract

The reactivity of the o- and p-quinones (II) and(IV) with various four-coordinated planar Co(II) complexes (I) is investigated by means of ESR and UV/VIS absorption spectroscopy. The 0-quinones add oxidatively producing Co(III) complexes (III) containing chelated o-semiquinone radical-anions. NO coordination of the fifth ligand in. the axial position is involved in thesereactions. All obser?ed oxidative additions are reversible; the position of the equili-brium depends strongly on the nature of the equatorial ligand. The extent of radicaladduct formation decreases in the order: dithioacetylacetonate > Schiff bases >dithiolates. When redox potentials of the reacting species are changed in a way thatmakes simple electron transfer between Co(II) complexes and quinones thermody-namically possible, the reduction of quinones to free semiquinone radical-anionsbecomes competitive with the oxidative addition. In the case of p-quinones, onlyelectron transfer is observed if the thermodynamic conditions are met. The structu-ral factors determining quinone reactivity are briefly discussed.