Atom transfer and rearrangement reactions catalyzed by methyltrioxorhenium, MTO

Methyltrioxorhenium (MTO) catalyzes the desulfurization of thiiranes by triphenylphosphine. Enormous enhancement in rate is observed when the catalyst is pretreated with hydrogen sulfide prior to the reaction. Using 2-mercaptomethylthiophenol as a ligand, we synthesized several model complexes to study the mechanism of this reaction. With suitable model systems, we were able to show that the active catalyst is a Re(V) species. The reactions are highly stereospecific and very tolerant to functional groups. As part of our studies, we synthesized and crystallographically characterized the first examples of neutral terminal and bridging Re(V)sulfidocomplexes. Some of these complexes undergo fast oxygen atom transfer reactions with organic and inorganic oxidants. Studies on these model complexes led us to the discovery that MTO catalyzes the selective oxidation of thiols to disulfides;The utility of MTO as a Lewis acid was exploited in effecting the rearrangement of propargylic alcohols to enones and enals. This reaction works efficiently with MTO when the propargyl alcohol is benzylic. The same chemistry when extended to allylic alcohols generates the more stable isomer at equilibrium. Kinetic, 2D and 18O labelling and theoretical studies were carried out to establish the mechanism of this reaction and to predict the direction of equilibrium in these systems;MTO activates hydrogen peroxide by forming a monoperoxo and a bisperoxocomplex both of which are efficient oxidants. Substituted arenes are selectively oxidized to p-quinones by the MTO/H2O2 system. The partially oxidized hydroquinones were detected in a few cases