Effect of Lewis base coordination on boryl radical reactivity: investigation using laser flash photolysis and kinetic ESR

The effect of Lewis base coordination on boryl radical reactivity (L -> BH2 center dot where L is triethylamine, 2-picoline, 4-dimethylaminopyridine, quinoline and diphenyl phosphine) is examined. Direct detection of the different boryl radicals, their transient absorption spectra, their interaction with double or triple bonds, oxygen, oxidizing agent, alkyl halides and their hydrogen lability have been studied using laser flash photolysis (LFP), kinetic ESR (KESR), ESR spin trapping and MO calculations. For example, a strong decrease of both the bond dissociation energy (BDE)(B-H) (33.8 kcal mol(-1)) and the addition rate constant to MA (1300 10(5) to >10(5) M(-1)s(-1)) was noted when going from the triethylamine borane to the quinoline borane complex, in line with the spin delocalization (1.04 vs. 0.19). These structures are also proposed as new highly efficient co-initiators for the acrylate photopolymerization. Copyright (C) 2009 John Wiley & Sons, Ltd.