Mechanism of 2,6-Dichloro-4,4′-bipyridine-Catalyzed Diboration of Pyrazines Involving a Bipyridine-Stabilized Boryl Radical

• Published in: Bulletin of the Chemical Society of Japan Vol. 94; no. 7; pp. 1894 - 1902
• Main Authors: Ohmura, Toshimichi, Morimasa, Yohei, Ichino, Tomoya, Miyake, Yusuke, Murata, Yasujiro, Suginome, Michinori, Tajima, Kunihiko, Taketsugu, Tetsuya, Maeda, Satoshi
• Format: Journal Article
• Language: English
• Published: The Chemical Society of Japan 01-07-2021
• Subjects: Organocatalyst; Diboration; Boryl radical
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.20210145

The mechanism of 4,4′-bipyridine-catalyzed diboration of pyrazines was studied by experimental observation of the intermediates 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 single-component 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.