Reactions of triphenylborane with photoexcited ketones and with diazodiarylmethanes

Aromatic ketones and diones when exposed to UV irradiation in the presence of triphenylborane give R2C-OBPh2 radicals through and SH2 displacement of phenyl from BPh3 by the excited triplet state of the carbonyl derivative. Very persisten radicals, characterized by g-factors higher than 2.0040, are obtained when boron is compelled to lie in the molecular plane owing to chelation by an electron-rich atom, such as oxygen (diones) or nitrogen. In some of these radicals, coupling of the unpaired electron with protons of the BPh2 group was also observed. Diazodiarylmethanes react spontaneously with triphenylborane by a heterolytic pathway, which eventually leads to the formation of triphenylmethyl radical.