Abstract
The compds. BPh3-nMesn (n = 0-3, Mes = mesityl), AlPh3, AlMes3, 1,4-Mes2BC6H4NMe2, 1,4-Mes2BC6H4BMes2 (I) and 4,4'-Mes2BC6H4C6H4BMes2 (II) were studied by UV/VIS spectroscopy and cyclic voltammetry. A single mesityl substituent is sufficient to permit reversible electron transfer at the electrode surface and to stabilize the singly reduced, i.e., radical anionic, form of triarylboranes by preventing an increase of the coordination no. at B. This electrochem. effect is not obsd. for the Al analogs. In contrast to the kinetic stabilization of triarylborane anion radicals by mesityl substituents stands the slight thermodn. destabilization by this electron-donor group. Disubstituted aroms. such as I and II show two-step reversible redox behavior. Spectroscopic and electrochem. results reveal that the dimesitylboryl substituent is a strong p acceptor, comparable to the nitrile group. on SciFinder(R)
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