Electronic Structure of 1,2‐Dihydro[1,3,2]diazaborolo[1,5‐ a ]pyridine in Comparison with the Parent Isoindole

Gas‐phase He‐I photoelectron spectra of N ‐ tert ‐butyl‐1,2‐dihydro[1,3,2]diazaborolo[1,5‐ a ]pyridine ( 3 ) and its thermolysis product, the parent compound 1 , have been recorded and assessed by density functional theory calculations. Similarly, N ‐ tert ‐butylisoindole ( 4 ) and the parent isoindole ( 2 ) were also studied. The first ionization energies of these compounds increase in the series 3 (6.75 eV) < 1 (6.85 eV) < 4 (6.9 eV) < 2 (7.3 eV). Interestingly, the HOMOs of 1 and 3 are destabilized with respect to the first ionization energy of the isomeric 1,3,2‐benzodiazaboroles (ca. 7.3 eV). The dipole moment of the ground state of isoindole derivative 4 (3.48 D) is significantly greater than that of 1,2‐dihydro[1,3,2]diazaborolo[1,5‐ a ]pyridine ( 3 ; 0.996 D). Upon electronic excitation, the dipole moments increased to 5.945 and 4.735 D for 4 and 3 , respectively.