Polymeric N-Heterocyclic Carbenes in Frustrated Lewis Pair Chemistry

The cooperative action of sterically bulky Lewis acids and bases forms frustrated Lewis pairs (FLPs) which activate and catalytically transform reactive substrates. Loading of these functional groups onto a polymer backbone has led to an established new field of stimuli-responsive materials capable of serving as recyclable catalysts. Poly(FLPs) were originally built from phosphine and borane-functionalized polymers, with recent work demonstrating the use of amines in these systems. Polymeric N-heterocyclic carbenes (poly(NHCs)) have been seldom explored in FLP chemistry. Herein, we explore the application of poly(NHCs) in a similar manner to our previously reported work. A styrene-based benzimidazolium functionalized copolymer was synthesized via controlled radical polymerization. Isolation of the active poly(NHC) proved challenging due to dimerization yielding a crosslinked network formed upon removal of solvent or precipitation. Application of the in-situ generated poly(NHC) through incorporation of boranes in various solvents was precluded either by coordination of the Lewis acid or the lack of carbene formation in non-coordinating solvents. Despite these challenges, using the poly(NHC) in conjunction with a highly Lewis acidic copolymer enabled the fixation of CS2 to form a covalently crosslinked poly(FLP) network.