Studies on the halide additives in the Ru-catalyzed hydroesterification

Abstract

The Ru-catalyzed hydroesterification using a chelation approach has an advantage of the insertion of carbonyl groups to olefins in the absence of carbon monoxide. In this approach, chelation plays an important role in effective suppression of decarbonylation. Since the reaction requires relatively high temperature and excess of substrate, several protocols have been examined to overcome these drawbacks. The presence of catalytic amounts of halide salts was found to enhance dramatically the reaction efficiency in the Ru-catalyzed hydroesterification of alkenes using a chelating 2-pyridylmethyl formate by lowering the reaction temperature. It showed great efficiency also in the hydroestrification of dienes and alkynes. With this milder condition, the substrate scope has been significantly broadened. On the other hand, the halide effect was not significant in the Ru-catalyzed hydroamidation, presumably due to the difference between the intermediates. On the basis of IR and NMR studies, the halide effect on the reaction was mainly attributed to the facile dissociation of the trirutheniumcarbonyl precursor into the presumed active metal species. Despite of efforts, we have not clarified the exact the active metal species, leaving us a room to further study in the future.