The Ligation of Phosphine Derivatives and the Oxygen-binding Properties of the Cobalt Mesoporphyrin IX Dimethyl Ester in Toluene

Abstract

Abstract The coordination of phosphine derivatives and some other bases to the cobalt mesoporphyrin IX dimethyl ester in toluene has been spectrophotometrically investigated. The coordination equilibrium constants were determined for each base, and found to be of this sequence (25 °C) : P(C4H9)3>>P(OCH3)3>P(C6H5)3>S(CH3)2>As(C6H5)3. The reversible oxygenation of the penta-coordinate complexes formed as above was investigated at lower temperatures (−20–−80 °C): the corresponding equilibrium constants were found to be in the following sequence (−80 °C): P(C4H9)3>P(OCH3)3>S(CH3)2>P(C6H5)3>As(C6H5)3. These relations were discussed in terms of the σ-donating ability of a ligand coordinated trans to oxygen.