Remote-controlled exchange rates by photoswitchable internal catalysis of dynamic covalent bonds

Abstract

The transesterification of boronate esters with diols is tunable over at least 14 orders of magnitude. Rate acceleration is achieved by internal base catalysis, which lowers the barrier for the proton transfer step. Here we report a photoswitchable internal catalyst that tunes the rate of boronic ester/diol exchange over at least 4 orders of magnitude. We employed an acylhydrazone molecular photoswitch, which forms a thermally stable but photoreversible intramolecular H-bond, to gate the activity of the internal base catalyst in 8-quinoline boronic esters. The photoswitch can be cycled repeatedly, with high photostationary states. The intramolecular H-bond is found to be essential to the design of this photoswitchable internal catalyst, as protonating the quinoline with external sources of acid has little effect on the exchange rate.