Unusual nitrene reactivity: imine formation in the photochemical reaction of a borylnitrene with ethene

Abstract

The cycloaddition of nitrenes with olefins is an important method for the synthesis of aziridines. We report here that the reaction of catecholato borylnitrene CatBN with ethene upon long wavelength photoirradiation (λ > 550 nm) gives not only the expected aziridine, but also the imine CatBNCHCH₃ under cryogenic matrix isolation conditions in solid neon at 4 K. Computational analysis reveals that the photochemically generated singlet CatBN (¹A₁ electronic state) can react with ethene to form the aziridine and a singlet 1,3-diradical intermediate. The latter arises from multi-state reactivity involving the nearly degenerate ¹A₁ and ¹A₂ nitrene singlet states. The singlet 1,3-diradical has a very low barrier for 1,2-H migration to give the imine. The observation of an imine in the reaction with an alkene reveals chemodivergence by highlighting a previously unobserved reactivity pathway in nitrene chemistry.