A comparative study on photocatalytic hydrogen transfer and catalytic hydrogenation of norbornadiene and quadricyclane catalyzed by [Rh6(CO)16

Abstract

Abstract The photo-assisted catalytic transfer hydrogenation and the catalytic hydrogenation of norbornadiene ( I ) and quadricyclane ( II ) over a photo-activated Rh cluster in 2-propanol in the presence of acetone was studied under comparative conditions. With the photo-assisted catalytic transfer hydrogenation, the hydrogen produced by dehydrogenation of 2-propanol is used very effectively for the addition to the reactants without evolving H 2 . Norbornane ( IV ) and nortricyclene ( V ) are formed in parallel in the photo-assisted hydrogen transfer reaction of II . In the reaction of I , the acetone-sensitized isomerization of I to II occurs prior to hydrogenation in a concentration of 58 mmol/l of I . However, at a lower concentration, we observed a stepwise hydrogenation of I to IV via norbornene ( III ). The yield of III formed in the catalytic hydrogenation was larger than that in the photo-assisted catalytic transfer hydrogenation. Compound II was not observed in the catalytic hydrogenation of I , and the yield of V was less than 1%. Compound II behaves in catalytic hydrogenation similar to as in photo-assisted catalytic transfer hydrogenation. The hydrogenation paths of I and II in both the reactions are discussed on the basis of a reaction mechanism shown in Scheme 1.