Triplet vinylnitrenes

Abstract

This chapter describes how intramolecular sensitization has been used to successfully form triplet vinylnitrene intermediates from vinyl azide, isoxazole, and azirine compounds. Triplet vinylnitrenes have been thoroughly characterized in cryogenic matrices using UV/vis absorption, infrared, and electron spin resonance spectroscopies. Electron spin resonance spectroscopy shows that vinylnitrenes have a significant 1,3‐biradical character, which is further supported by density functional theory calculations. Laser flash photolysis, which has allowed the direct detection of triplet vinylnitrenes in solution, reveals that they are short‐lived intermediates with lifetimes on the order of a few microseconds. Vinylnitrenes decay efficiently by intersystem crossing to form products because their 1,3‐biradical character renders their vinylic CC bond flexible, which enhances intersystem crossing. At cryogenic temperatures, flexible triplet vinylnitrenes are not stable and intersystem cross to form products. Nevertheless, triplet vinylnitrenes can be stabilized by limiting the flexibility of the vinylic CC bond, which renders them stabile in cryogenic matrices. Thus, they are promising building blocks for high‐spin assemblies. Furthermore, as stabilized vinylnitrenes can also be employed in bimolecular reactions, they have potential for use in various synthetical applications.