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

Abstract

The oxidation potentials Eox of a series of 2,3-dihydro-1H-1,3,2-diazaboroles (1a−i) and of the corresponding saturated 1,3,2-diazaborolidines 2a (R = NH2), 2b (OMe), 2c (Me), 2d (NMe2), 2e (H), 2f (SMe), 2g (SnMe3), 2h (Br), 2i (CN) were determined by cyclovoltammetry in CH2Cl2 solution. The potentials Eox of the irreversible electrochemical oxidations range from Eox = −288 mV (1a) to 752 mV (1i). In contrast to this, Eox 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-1H-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)].