In this computational study, the thermodynamics of hydrogen, hydride, and proton transfer from 22 phosphonium-borohydride intramolecular and intermolecular frustrated Lewis pairs (FLPs) to eight probe substrates was investigated. The purpose of this study was to gain insight into the thermodynamics of H transfer with intramolecular phosphonium-borohydrides; to determine whether intramolecular or intermolecular FLPs are preferred in FLP-catalyzed hydrogenation reactions. Comparison of the computed thermodynamic values showed that by connecting a borohydride and phosphonium center through a linker, H loss from the respective intramolecular phosphonium-borohydride became less favorable by about five and seven kcal mol in acetonitrile and toluene, respectively. Connecting the borohydride and phosphonium centers also resulted in both hydride and proton loss becoming less favorable, on average, by about 10.0 kcal mol and about 4.6 pK units, respectively. Analysis of hydrogen, proton, and hydride transfer to eight probe substrates showed that initial proton transfer is 49 and 20 kcal mol more favorable than the initial hydride transfer in the reduction of nitrogen-containing and oxygen-containing unsaturated substrates, respectively. These results suggest that proton transfer, followed by hydride transfer occurs in the reduction of imines, ketones, aldehydes, and enamines. From the thermodynamic analysis of proton and hydride transfer, an intramolecular phosphonium-borohydride was the desired catalyst for the reduction of imines and enamines, while an intermolecular phosphonium-borohydride was the favored catalyst for the reduction of ketones and aldehydes.
In this computational study, the thermodynamics of H 2 , proton, and hydride transfer from 13 ammonium borohydride and six phosphonium borohydride intramolecular and intermolecular frustrated Lewis pairs (FLPs) was probed to gain insight into whether intramolecular or intermolecular aminecontaining FLPs are preferred to phosphine-containing FLPs in FLP-catalyzed hydrogenation reactions. H 2 , hydride, and proton transfer from intramolecular ammonium borohydrides was, on [a]
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.