Acceptorless Alkane Dehydrogenation Catalyzed by Iridium CCC-Pincer Complexes

Iridium
complexes of CCC-pincer bis-N-heterocyclic carbenes, including
a newly synthesized trifluoromethyl-substituted complex, were examined
as catalysts for the acceptorless dehydrogenation of cyclooctane and n-undecane. Up to 103 turnovers were observed for the dehydrogenation
of cyclooctane, and up to 97 turnovers were observed for the dehydrogenation
of n-undecane. The catalysts showed high initial
turnover frequencies, followed by a gradual loss of activity over
24 h. Experiments indicate that this loss of activity is due to catalyst
decomposition rather than product inhibition. Stoichiometric reactivity
was investigated for the precatalysts, focusing on the synthesis of
dihydride and trihydride complexes as well as the dissociation and
addition of neutral ligands.

本研究将CCC型钳形双氮杂环卡宾（CCC-pincer bis-N-heterocyclic carbenes）铱配合物作为催化剂，考察其在环辛烷与正十一烷无受体脱氢反应中的催化性能，其中涵盖一款新合成的三氟甲基取代配合物。实验结果显示，环辛烷脱氢反应的最高周转数可达103，正十一烷脱氢反应的最高周转数可达97。该类催化剂初始周转频率较高，但在24小时内活性逐渐衰减。实验表明，该活性衰减源于催化剂分解而非产物抑制。此外，本研究针对预催化剂开展了化学计量反应性研究，重点聚焦二氢化物与三氢化物配合物的合成，以及中性配体的解离与加成过程。