Photoinduced Dehydrogenative Borylation via Dihydrogen Bond Bridged Electron Donor and Acceptor Complexes

Air-stable amine- and phosphine-boranes are discovered as donors to integrate with pyridinium acceptor for generating photoactive electron-donor-acceptor (EDA) complexes. Experimental results and DFT calculations suggest a dihydrogen bond bridging the donor and acceptor. Irradiating the EDA complex enables an intra-complex single electron transfer to give a boron-centered radical for dehydrogenative borylation with no need of external photosensitizer and radical initiator. The deprotonation of Wheland-like radical intermediate rather than its generation is believed to determine the good ortho-selectivity based on DFT calculations. A variety of alpha-borylated pyridine derivatives have been readily synthesized with good functional group tolerance.

Automated summary

Air-stable amine- and phosphine-boranes have been discovered as donors to form photoactive electron-donor-acceptor (EDA) complexes with pyridinium acceptor. The EDA complex, upon irradiation, undergoes intra-complex single electron transfer without the need for external photosensitizer and radical initiator, leading to the formation of a boron-centered radical for dehydrogenative borylation. DFT calculations suggest that the deprotonation of the Wheland-like radical intermediate, rather than its generation, determines the good ortho-selectivity. Various alpha-borylated pyridine derivatives can be easily synthesized with good functional group tolerance.