UV-Photoelectron Spectroscopic Studies of the Simplest 2,3-Dihydro-1H-1,3,2-diazaboroles [(CHNH)2BX, X = H, CN]

Flash vacuum thermolysis of N,N′‐di‐tert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole (1) and N,N′‐di‐tert‐butyl‐2‐cyano‐2,3‐dihydro‐1H‐1,3,2‐diazaborole (2) has been performed with a progressive increase in temperature and direct analysis of the gaseous flow by UV‐photoelectron spectroscopy. The generation of isobutene was confirmed by its PE bands, and the formation of 2,3‐dihydro‐1H‐1,3,2‐diazaborole (1′) and 2‐cyano‐2,3‐dihydro‐1H‐1,3,2‐diazaborole (2′) has also been evidenced. These experimental results have been corroborated by TDDFT and OVGF calculations of the ionization energies. The elusive 2,3‐dihydro‐1H‐1,3,2‐diazaborole (1′) has been generated by flash vacuum thermolysis of N,N′‐di‐tert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole (1) and studied by UV‐photoelectron spectroscopy. The HOMO of 1′ is destabilized by 0.3 eV in comparison with that of pyrrole, whereas the HOMO–1 is significantly stabilized (0.9 eV).