Spontaneous and photoinduced formation of radical anions in the reaction of borohydrides with unsaturated compounds

The spontaneous and photoinduced reactions of tetrabutylammonium borohydride, B u ~BNH 4, with a number of quinones, ketones, cyano derivatives and nitrogen-containing heteroaromatic bases have been studied by means of EPR spectroscopy in benzene and in ethereal solvents. In the absence of UV irradiation, formation of radical anions resulting from electron transfer from the borohydride negative ion, BH,-. to the organic substrate has been detected with compounds having reduction potentials less negative than -1.5 V vs. SCE. With the less easily reducible compounds, UV irradiation leads in some cases to radical anions produced by photoinduced ET and in other cases to radical adducts of the borane radical anion, BH3'-.