Absolute rate constants for some reactions of the triethylamineboryl radical and the borane radical anion

Laser flash photolysis (LFP) of di-tert-butyl peroxide or dicumyl peroxide at ambient temperatures in the presence of Et3N-->BH3 or BH4- generated the title radicals which were found to have broad, featureless absorptions in the visible region. Rate constants for H-atom abstraction from Et3N-->BH3 by cumyloxyl radicals show a small solvent dependence, e.g. 12 x 10(7) and 2.2 x 10(7) dm(3) mol(-1) s(-1) in isooctane and acetonitrile, respectively. Rate constants for halogen atom abstraction by Et3N-->BH2. and BH3.- from a number of chlorides and bromides were determined by LFP and by competitive kinetics, e.g., for Et3N-->BH2. + CCl4/PhCH2Cl/CH3(CH2)(2)Cl, k = 4.4 x 10(9)/1.1 x 10(7)/5.1 x 10(5) dm(3) mol(-1) s(-1) and for BH3.- + CCl4/PhCH2Cl, k = 2.0 x 10(9)/3.0 x 10(7) dm(3) mol(-1) s(-1). Rates of addition of Et3N-->BH2. to 1- and 1,1-substituted olefins increase dramatically as the electron affinity of the olefin increases, confirming the nucleophilic character of amine-boryl radicals. A comparison of the present results with literature data for the addition of olefins of four nucleophilic carbon-centered radicals proves that Et3N-->BH2. is by far the most nucleophilic radical for which kinetic data are available. A few rate constants for abstraction of hydrogen from electron-deficient carbon by Et3N-->BH2. are also reported.