Solid-state synthesis of molybdenum and tungsten porphyrins and aerial oxidation of coordinated benzenethiolate to benzenesulfonate

Abstract

A new route is developed for the synthesis of molybdenum and tungsten porphyrins using [M(NO)₂py₂Cl₂] (M = Mo, W) as the metal source and TPP (dianion of 5,10,15,20-meso-tetraphenylporphyrin) in the benzoic acid melt. Complexes [Mo^VO(TPP)(OOCPh)] (1) and [W^VO(TPP)(OOCPh)] (2) are isolated in almost quantitative yield. These are characterized by single-crystal X-ray structure analysis, electron paramagnetic resonance, electronic and IR spectroscopy, and magnetic moment measurements. Benzenethiol substitutes for PhCOO^– in 1, forming an intermediate thiolato complex that responds to the intramolecular redox reaction across the Mo^V–SPh bond to yield [Mo^IVO(TPP)] (3). Under an excess of benzenethiol, PhS^– is coordinated to the vacant site in 3, which under aerial oxidation is oxidized to benzenesulfonate to form [Mo^VO(TPP)(O₃SPh)] (4). 2 undergoes similar aerial oxidation chemistry albeit slowly.