Synthetic, Cyclovoltammetric, and UV-Photoelectron Spectroscopic Studies of 2,3-Dihydro-1H-1,3,2-diazaboroles and 1,3,2-Diazaborolidines

The oxidation potentials E ox of a series of 2,3-dihydro-1 H -1,3,2-diazaboroles ( 1a − i ) and of the corresponding saturated 1,3,2-diazaborolidines 2a (R = NH 2 ), 2b (OMe), 2c (Me), 2d (NMe 2 ), 2e (H), 2f (SMe), 2g (SnMe 3 ), 2h (Br), 2i (CN) were determined by cyclovoltammetry in CH 2 Cl 2 solution. The potentials E ox of the irreversible electrochemical oxidations range from E ox = −288 mV ( 1a ) to 752 mV ( 1i ). In contrast to this, E ox of the corresponding diazaborolidines are anodically shifted by 260 mV ( 1d, 2d ) to 752 mV ( 1b, 2b ) and vary from 280 mV ( 2a ) to 1164 mV ( 2i ). Gas-phase photoelectron spectra of representatives of both series of compounds were recorded and assessed by density functional calculations. The first ionization potentials of the 2,3-dihydro-1 H -1,3,2-diazaboroles range in the series 1c (7.1 eV) < 1f (7.3 eV) < 1e = 1h (7.4 eV) < 1i (7.7 eV). They differ by less than 0.3 eV from the first ionization potentials determined for the saturated analogues [1st IP for 2c (7.3 eV) < 2e = 2f (7.4 eV) < 2h (7.7 eV)].