Catalysis of Organic..

Moses et al. 17SnCOSnMe 4≡SiOReO 3Sn≡SiOSnMe 3ReSi- 4 kJ/molSiReCMeReO 3Scheme 2 Reaction of perrhenate attached to silsesquioxane cube (a computationalmodel for the silica surface) with SnMe 4 is predicted to liberate MeReO 3 .Although perrhenate/silica is not itself active as an olefin metathesis catalyst, themodel reaction shown in Scheme 2 is of interest because the expected product,MeReO 3 , does not chemisorb onto silica, and can therefore be recovered. Toinvestigate this prediction, perrhenate/silica was prepared according to a literaturemethod (13). A sample of silica was first calcined at 1100 °C for 23 h to generatestrained siloxane-2 rings (0.12/nm 2 ), eq 1. This material was treated with Re 2 O 7vapor at 250°C under 250 Torr O 2 , to generate cleanly the silica-supportedperrhenate in the absence of water, eq 2.HOSiHOO SiH 2 OSiOO Si(1)O OORe O Re OOOReO + OO OOSiO SiSiOReOO OO Si(2)