Keller John W, Ayudhya Theppawut I, Dingra Nin N
Department of Chemistry and Biochemistry, University of Alaska Fairbanks Fairbanks AK 99775-6160 USA
Department of Chemistry, University of Texas of the Permian Basin Odessa TX 79762 USA.
RSC Adv. 2020 Apr 24;10(27):16038-16044. doi: 10.1039/d0ra01572e. eCollection 2020 Apr 21.
Trimethylamine-boranecarboxylic acid (CH)N-BHCOOH and other amine carboxyboranes have been observed to undergo slow decarbonylation in neutral aqueous solution. This reaction, when it occurs , may have a therapeutic effect by delivering low concentrations of carbon monoxide over an extended period. In order to identify a possible mechanistic pathway for decarbonylation, the smallest tertiary amine derivative and its corresponding carboxylate ion were studied using CCSD(T)/PCM/6-311++G(2d,p)//M06-2X/PCM/6-311++G(2d,p) model chemistry. The proposed mechanistic pathway begins with a trimethylamine boranecarboxylate ion, which first undergoes an internal substitution reaction (Si) to give free amine and the carboxyborane anion BHCOO. The latter cyclic ion then releases CO a rapid chelotropic fragmentation. The role of water solvent in these reactions was explored by structural and energetic analysis of hydrogen-bonded complexes. It was found that complexation with water inhibits dissociation of trimethylamine by stabilizing the trimethylamine carboxyborane anion, whereas water accelerates CO loss by stabilizing the polar chelotropic transition state.
三甲胺 - 硼烷羧酸（(CH)N - BHCOOH）及其他胺基羧基硼烷已被观察到在中性水溶液中会缓慢脱羰。该反应一旦发生，可能通过长时间释放低浓度一氧化碳而产生治疗效果。为了确定脱羰可能的反应机理途径，使用CCSD(T)/PCM/6 - 311++G(2d,p)//M06 - 2X/PCM/6 - 311++G(2d,p)模型化学方法研究了最小的叔胺衍生物及其相应的羧酸根离子。所提出的反应机理途径始于三甲胺硼烷羧酸根离子，它首先进行分子内取代反应（Si）生成游离胺和羧基硼烷阴离子BHCOO。然后，后者的环状离子通过快速的螯合碎裂释放出CO。通过对氢键复合物的结构和能量分析，探索了水溶剂在这些反应中的作用。研究发现，与水形成复合物通过稳定三甲胺硼烷羧酸根阴离子来抑制三甲胺的解离，而水则通过稳定极性螯合过渡态来加速CO的损失。
