Low-Temperature Dehydrogenation of Cyclooctane by Using Pincer Iridium Complexes Bearing an N,N′-Diarylated PNCNP Ligand
Low-Temperature Dehydrogenation of Cyclooctane by Using Pincer Iridium Complexes Bearing an N,N′-Diarylated PNCNP Ligand
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DOI：
10.1021/acscatal.3c01739
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发表时间：
2023-05
期刊：
影响因子：
12.9
通讯作者：
Naoto Uno;R. Nakano;M. Yamashita
中科院分区：
文献类型：
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作者：
Naoto Uno;R. Nakano;M. Yamashita
含有芳基硝基的PNCNP钳形Ir络合物(−N(Ar)−)在低温条件下催化环辛烷的转移脱氢，在125℃时以叔丁乙烯为转化率200，以环己烯(CHE)为牺牲氢受体在50℃时转化率为60。尽管以前的报道涉及到含有二(异丙基)磷胺侧臂的钳形Ir络合物的合成困难，但我们的设计使用了化学惰性(3，5-二取代芳基)硝基连接物，从而成功地与Ir络合。结构表征和计算研究表明，芳基硝基提供的空间拥堵破坏了静止的内部烯烃加合物的稳定性，从而降低了限速C-H加成反应的总活化势垒。空间堵塞也阻碍了胆碱酯酶不希望发生的歧化，使其成为有效的氢受体。由于它们的直接合成以及通过芳基上的3，5-取代基进行的良好的可调性，因此，本工作中提出的N‘-二芳基PNCNP配体将是非常成功的PCP钳形框架的有价值的补充。
PNCNP pincer iridium complexes possessing arylnitrene linkers (−N(Ar)−) catalyze transfer dehydrogenation of cyclooctane (COA) under low-temperature conditions, giving 200 turnovers at 125 °C usingtert-butylethylene (TBE) and 60 turnovers at 50 °C using cyclohexene (CHE) as a sacrificial hydrogen acceptor. Despite prior reports dealing with the synthetic difficulty of pincer iridium complexes bearing di(isopropyl)phosphoramine sidearms, our design using chemically inert (3,5-disubstituted-aryl)nitrene linkers allowed for the successful complexation with iridium. The structural characterization and computational study revealed that steric congestion provided by arylnitrene linkers destabilizes the resting internal alkene adducts, thereby reducing the overall activation barrier of the rate-limiting C–H addition. The steric congestion also hinders undesirable disproportionation of CHE, allowing for its use as an effective hydrogen acceptor. With their straightforward synthesis coupled with fine tunability through the 3,5-substituents on the aryl groups, theN,N′-diarylated PNCNP ligands presented in this work will be a valuable addition to the highly successful PCP pincer framework.