Molybdenum(VI)-dioxo complexes with sterically bulky thiocarboxylate ligands. Reactions with aliphatic thiols and electrochemical properties

Abstract

Under acid conditions, the reaction of (Bu n 4N)2[Mo VIO 2(O 2CC(S)Ph 2) 2] with aliphatic thiols yields the monomeric [Mo VO(O 2CC(S)Ph 2) 2] − as unique complex product. The experimental pseudo-first order rate constant with respect to the Mo(VI) complex was found to be K=6.1 × 10 −5 s −1. At neutral pH, however, an unstable Mo(IV) species was formed which was also electrochemically detected in a reversible Mo(V,IV) couple. [Mo VO(O 2CC(S)Ph 2) 2] − appears to be obtained by the reaction of [Mo IVO(O 2CC(S)Ph 2) 2] 2− with unreacted [Mo VIO 2(O 2CC(S)Ph 2) 2] 2−. Steric features on the ligand (gemdiphenyl groups) explain that the latter reaction does not lead to the expected formation of μ-oxo Mo(V) dimers. [Mo VO(O 2CC(S)Ph 2) 2]− undergoes a one-electron reversible reduction on the cyclic voltammogram time scale, being also oxidized by nitrate ions to the starting Mo(VI) complex. The relation of these results to enzymatic systems is briefly discussed.