METAL-ION MEDIATED DEOXYGENATION OF SULFOXIDES

Over the past two decades, the deoxygenation (i.e. the reduction of th e sulfinyl group) of free sulfoxides, R(2)S=O, has been extensively st udied and described in a number of reviews. However, the deoxygenation of coordinated sulfoxide ligands and metal-ion mediated deoxygenation of sulfoxides has received much less attention and no general overvie w of these processes has been presented. Correcting that omission is t he major goal of this review. Although details of syntheses that invol ve the deoxygenation of sulfoxide ligands are presented, particular em phasis is placed on discussion of both the common features and differe nces in the reactions of S- and O-bonded sulfoxides. Along with genera l consideration of experimental results, an attempt, is made to show t hat most of the methods for the reduction of the very strong S-O bond in S-coordinated R(2)SO ligands are based on an initial activation of the sulfinyl oxygen by a reagent having a highly reactive electrophili c center. In contrast, in the case of O-bound sulfoxides, the metal io n itself plays the role of the electrophilic reagent and thus promotes the deoxygenation reaction. In order to provide a clearer picture of sulfoxide deoxygenation reactions, possible reaction pathways are disc ussed and evidence for these mechanisms is provided.