The different kinetic and mechanistic behaviors of molybdenum and tungsten in the reduction of tris(benzene‐1,2‐dithiolato)Mo(VI) and W(VI) complexes by ascorbic acid in aqueous media

Abstract

The mono-electronic reduction of tris(benzene-1,2-dithiolato)Mo(VI) and W(VI) complexes (ML 3 : M = Mo, W; L = S 2 C 6 H 2− 4 , S 2 C 6 H 3 CH 2− 3 ) to their anionic forms ML − 3 by L(+)-ascorbic acid (H 2 A) has been studied in tetrahydrofurane (THF):water and THF:methanol by means of diode-array, stopped-flow, and mass spectrometry-electrospray ionization (MS-ESI) spectroscopy. The kinetic study in methanol demonstrates that the reaction is first order in each reactant, the electron transfer being rate limiting. This fact was assessed by the absence of a primary saline effect and by the correlation observed between the activation free enthalpy ( G = ) and the reduction potentials measured by cyclic voltamperometry. In aqueous media, Mo(VI)-tris(dithiolenes) also reduce to their Mo(V) anionic forms. The reaction obeys the rate law −d [ML 3 ]/dt = (k S + k A [H 2 A] T )[ML 3 ] (M = Mo), in agreement with a parallel kinetic scheme Correspondence to: Francisco Pérez-Pla; e-mail: francisco .perez@uv.es.Supporting Information is available in the online issue at wileyonlinelibrary.com.