A Bifunctional Iridium Catalyst Modified for Persistent Hydrogen Generation from Formic Acid: Understanding Deactivation via Cyclometalation of a 1,2-Diphenylethylenediamine Motif
A Bifunctional Iridium Catalyst Modified for Persistent Hydrogen Generation from Formic Acid: Understanding Deactivation via Cyclometalation of a 1,2-Diphenylethylenediamine Motif
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DOI：
10.1021/acscatal.7b01068
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发表时间：
2017-07-01
期刊：
影响因子：
12.9
通讯作者：
Kayaki, Yoshihito
中科院分区：
文献类型：
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作者：
Matsunami, Asuka;Kuwata, Shigeki;Kayaki, Yoshihito
研究了具有1,2 - 二苯乙二胺（DPEN）骨架的双功能铱配合物的热降解，这与甲酸无受体脱氢过程中催化剂的失活有关。由N - 三氟甲磺酰基 - 1,2 - 二苯乙二胺（TfDPEN）衍生的结构明确的氢化铱配合物1b，在1,2 - 二甲氧基乙烷（DME）的回流温度下，经二胺主链上苯取代基邻位碳原子的C - H键断裂，仅转化为两种铱环化合物（2和3）。这些产物通过核磁共振、元素分析和X射线晶体学成功分离和表征。在水存在的情况下，铱环的形成显著增强，这可能是由于通过羟基铱中间体更容易进行去质子化的邻位金属化反应。为了防止由DPEN部分的环金属化导致的失活过程，从N - 三氟甲磺酰基乙二胺（TfEN）合成了一种无苯取代基的氢化铱配合物（5b）。改性后的配合物5b在水和DME的1/1混合溶剂中，即使在没有碱添加剂的情况下，也显示出显著的催化甲酸析氢能力。相对于1b，其初始速率能保持更长时间，因此在60℃、HCOOH/5b比值为15900的条件下，甲酸在80分钟内大部分被转化。
Thermal degradation of a bifunctional Ir complex with a 1,2-diphenylethylenediamine (DPEN) framework was investigated, which is relevant to catalyst deactivation in the acceptorless dehydrogenation of formic acid. The well-defined hydridoiridium complex 1b, derived from N-triflyl-1,2-diphenylethylenediamine (TfDPEN), proved to be solely transformed at the reflux temperature of 1,2-dimethoxyethane (DME) into two iridacycles (2 and 3) via C-H bond cleavage at the ortho carbon atoms of the phenyl substituents on the diamine backbone. These products were successfully isolated and characterized by NMR, elemental analysis, and X-ray crystallography. The iridacycle formation was significantly enhanced in the presence of water, possibly due to facile deprotonative orthometalation via a hydroxidoiridium intermediate. To prevent the deactivation process caused by the cyclometalation of the DPEN moiety, a hydridoiridium complex (5b) without phenyl substituents was synthesized from N-triflylethylenediamine (TfEN). The modified complex 513 showed a pronounced ability to catalyze hydrogen evolution from formic acid in a 1/1 mixed solvent of water and DME even in the absence of base additives. The initial rate was maintained for a longer time relative to 1b, and thus formic acid was mostly converted within 80 min under the conditions of a HCOOH/5b ratio of 15900 at 60 degrees C.