Modulation of Isomerization and Ligand Exchange Rates by π Bonding in Bis(iminoxolene)iridium Pyridine Complexes
Modulation of Isomerization and Ligand Exchange Rates by π Bonding in Bis(iminoxolene)iridium Pyridine Complexes
复制标题
双(亚胺氧杂环戊烯)铱吡啶配合物中α键对异构化和配体汇率的调节
DOI：
10.1021/acs.inorgchem.3c01717
复制
发表时间：
2023
影响因子：
4.6
通讯作者：
Brown, Seth N.
中科院分区：
文献类型：
--
作者：
Do, Thomas H.;Haungs, David A.;Chin, William Y.;Jerit, Jack T.;VanderZwaag, Analena;Brown, Seth N.
双(亚氨基氧杂环戊烯)铱配合物(Diso)2IrCl (Diso =N-(2,6-二异丙基苯基)-4,6-二叔丁基-2-亚氨基-邻苯醌)与吡啶反应生成反式-(Diso)2Ir(py)Cl作为动力学产物，加热时形成顺式-(Diso)2Ir(py)Cl作为唯一的热力学产物。电子谱和密度泛函理论计算表明顺式和反式异构体的电子结构非常相似，具有非键合的亚氨基氧杂环戊烯中心HOMO和金属-亚氨基氧杂环戊烯π* LUMO。顺式-(Diso)2Ir(py)Cl 和顺式-[(Diso)2Ir(py)2]+（但不是反式-(Diso)2Ir(py)Cl）的三重态能量异常低（比单重态高 1000–1500 cm–1），如变温 NMR 光谱所示。低能三重态归因于亚氨基氧杂环戊烯中二面角的变化，这允许在反式八面体化合物中无法实现的部分π相互作用。甲苯中反式-顺式异构化的机理研究表明，反应通过五配位物质异构化为具有顺式亚氨基氧杂环戊烯配体和顶端氧的形式进行。这种形式的能量很高，因为失去了次级亚氨基氧杂环戊烯与铱 π 供体相互作用，这种相互作用在反式形式中是可能的，但在方锥结构的顺式形式中则不然。由于 N-芳基取代基与吡啶的相互作用，这种立体电子效应与吡啶 intrans-(Diso)2Ir(py)Cl 的较差结合相结合，使得吡啶在室温下从反式异构体上解离的速度加快了 108 倍。
The bis(iminoxolene)iridium complex (Diso)2IrCl (Diso =N-(2,6-diisopropylphenyl)-4,6-di-tert-butyl-2-imino-o-benzoquinone) reacts with pyridine to givetrans-(Diso)2Ir(py)Cl as the kinetic product, withcis-(Diso)2Ir(py)Cl formed as the exclusive thermodynamic product upon heating. Electronic spectra and density functional theory calculations point to very similar electronic structures for the cis and trans isomers, with a nonbonding iminoxolene-centered HOMO and a metal–iminoxolene π* LUMO. The triplet states ofcis-(Diso)2Ir(py)Cl andcis-[(Diso)2Ir(py)2]+(but nottrans-(Diso)2Ir(py)Cl) are unusually low in energy (1000–1500 cm–1above the singlets), as shown by variable-temperature NMR spectroscopy. The low-energy triplets are attributed to a change in dihedral angle in the iminoxolenes, which allows a partial π interaction that cannot be achieved in the trans octahedral compounds. Mechanistic studies of the trans–cis isomerization in toluene indicate that the reaction proceeds via isomerization of the five-coordinate species to a form with cis iminoxolene ligands and an apical oxygen. This form is high in energy due to the loss of a secondary iminoxolene-to-iridium π-donor interaction that is possible in the trans form but not in the cis form for the square pyramidal structures. This stereoelectronic effect, combined with the poorer binding of pyridine intrans-(Diso)2Ir(py)Cl due to the interactions of theN-aryl substituents with the pyridine, makes the pyridine dissociate faster from the trans isomer by a factor of 108at room temperature.