Different reaction behaviour of molybdenum and tungsten – Reactions of the dichloro dioxo dimethyl-bispyridine complexes with thiophenolate

The reaction of the metal complexes MO2Cl2(mebipy) (M = Mo, W) with two equivalents thiophenol by the exact same procedure leads to two different products for molybdenum [Mo2O4(SPh)2(mebipy)2] and tungsten [WO2(SPh)2(mebipy)]. To understand why this is the case the redox potentials of the starting materials were measured showing that the redox potential for thiophenol is lower than the redox potentials (MV ↔ MVI) for both of the metal precursors. A reduction of the metal and oxidation of the sulfur should be possible for both reactions but occurs only for the molybdenum compound. Theoretical calculations show that different metal–sulfur bond strengths are as well and equally responsible for the differing reaction behaviour as are the redox potentials.