Supported Re Catalysts for Metathesis of Functionalized Olefins

The molecular role of organotin promoters, which confer functional group tolerance on supported Re catalysts for olefin metathesis, was explored through spectroscopic and computational analysis, as well as kinetic studies. On dehydrated silica and silica-alumina, the addition of SnMe4 results in two surface reactions: (i) in situ generation of MeReO3; and (ii) capping of Bronsted acid sites. The former is responsible for catalytic activity towards polar α-olefins; thus, an independentlyprepared sample of MeReO3/silica-alumina catalyzed the homometathesis of methyl3-butenoate. The latter stabilizes the catalyst: in sequential batch reactor tests involving propylene homometathesis, MeReO3 deposited on silica-alumina capped with hexamethyldisilazane (to eliminate Bronsted acidity) showed activity identical to that of the perrhenate/silica-alumina catalyst promoted with SnMe4. Thus, a completely Sn-free catalyst performs metathesis as efficiently as the organotincontaining perrhenate catalyst.