Cyclopentane/deuterium exchange on palladium-gold and palladium-tin alloy films

Abstract

The cyclopentane/deuterium exchange reaction has been studied on well-homogenized Pd–Au and Pd–Sn alloy films. The efficiency of “roll-over” of cyclopentene intermediate (as measured by the ratio two-set/one-set exchanged product) was unaffected by alloying Pd with Au but was increased by alloying with Sn. This finding is discussed in terms of the electronic effects of Au and Sn solutes on the palladium–alkene bond. In both alloy systems the activity-composition plots show a decrease in the absolute rate of exchange of 3–4 orders of magnitude. For Pd–Au this break occurs at 30–40 atom % Pd whilst for Pd–Sn it occurs at 85–90 atom % Pd. Initial product distributions arising from carbene species were found on Pd alloys of > 80 atom % Au and of > 15 atom % Sn. A comparison of the effects of alloying Pd with gold on the rates of exchange and deuteriolysis supports the view that the former reaction requires smaller surface ensembles than the latter.