The formation of epoxides from reactions of oxametallacycles on Ag(110): Adensity functional theory study

Density functional theory (DFT) cluster calculations have been used to inve stigate the interaction of various oxametallacycle, intermediates with the Ag(110) surface, with an emphasis on connecting oxametallacycle structure t o the mechanism of olefin epoxidation. These studies indicate that two type s of oxametallacycle structures may be formed on Ag(110): the OMME structur e, which incorporates a silver dimer in the oxametallacycle ring, and the O ME structure, which incorporates a single silver atom. Although OMME-type i ntermediates are calculated to be more thermodynamically stable for monofun ctional epoxides (such as ethylene oxide), transition-state calculations su ggest that OME oxametallacycles may be more likely structures along the rea ction coordinate for olefin epoxidation. OME structures have also been iden tified as likely intermediates in the synthesis of multifunctional epoxide molecules such as 1-epoxy-3-butene (EpB). In these cases, the extra functio nal group can also bind to the surface to increase the heat or adsorption o f the oxametallacycle intermediate. These calculations indicate that oxamet allacycles may be important intermediates in silver-catalyzed epoxidation r eactions and that differences in oxametallacycle stability may explain diff erences observed in the epoxidation kinetics of different olefins.