Mechanism Of 2,6-Dichloro-4,4 '-Bipyridine-Catalyzed Diboration Of Pyrazines Involving A Bipyridine-Stabilized Boryl Radical

The mechanism of 4,4'-bipyridine-catalyzed diboration of pyrazines was studied by experimental observation of the inter-mediates and by theoretical calculations. Intermediary radical species were detected by ESR measurement of the reactions of 2,6-dichloro-4,4'-bipyridines with bis(pinacolato)diboron and identified by simulation. Based on these observations, radical processes involving 4,4'-bipyridine-stabilized boryl radicals were evaluated by DFT calculations combined with singlecomponent artificial force induced reaction (SC-AFIR). The results of calculations indicate that a radical transfer process from 4,4'-bipyridine-stabilized boryl radical to pyrazine is a major pathway in the catalytic reaction. The origin of the high catalytic efficiency of 2,6-dichloro-4,4'-bipyridine is ascribed to the effect of the chlorine atom on the stability of the corresponding N,N'-diboryl-4,4'-bipyridinylidene.