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.

中文翻译：

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2,6-二氯-4,4'-联吡啶催化吡嗪二硼化反应的机理涉及联吡啶稳定的硼基自由基

通过中间体的实验观察和理论计算，研究了4,4'-联吡啶催化吡嗪二硼化反应的机理。通过 2,6-二氯-4,4'-联吡啶与双（频哪醇）二硼反应的 ESR 测量检测中间自由基物种，并通过模拟进行鉴定。基于这些观察结果，通过 DFT 计算结合单组分人工力诱导反应 (SC-AFIR) 评估了涉及 4,4'-联吡啶稳定的硼基自由基的自由基过程。计算结果表明，从 4,4'-联吡啶稳定的硼基自由基到吡嗪的自由基转移过程是催化反应的主要途径。2,6-二氯-4,4'催化效率高的由来N , N' -diboryl-4,4'-bipyridinylidene。