Synthesis of Boriranes by Double Hydroboration Reactions of N‑Heterocyclic Carbene Boranes and Dimethyl Acetylenedicarboxylate

Reaction
of bis-(2,6-diisopropylphenyl)-imidazol-2-ylidene
borane with dimethyl acetylenedicarboxylate gives 80% yield of a stable
borirane (boracyclopropane) formed by formal double hydroboration
along with 5% of the (E)-alkenylborane. DFT calculations
suggest a mechanism where divergence to the two products occurs after
a common initial stage of hydride transfer from the NHC-borane to
the acetylenedicarboxylate.

双(2,6-二异丙基苯基)咪唑-2-亚基硼烷与丁炔二酸二甲酯（dimethyl acetylenedicarboxylate）发生反应，以80%的收率得到一种经形式双重氢硼化反应生成的稳定硼杂环丙烷（boracyclopropane，又称硼丙环），同时以5%的收率生成(E)-烯基硼烷。密度泛函理论（DFT, Density Functional Theory）计算显示，该反应的机理为：在从氮杂环卡宾硼烷（NHC-borane）向丁炔二酸二甲酯发生氢负离子转移的共同初始步骤后，反应路径发生分岔，最终得到两种产物。