Tuning Cyclohexane Oxidation: Combination of Microwave Irradiation and Ionic Liquid with the C‑Scorpionate [FeCl2(Tpm)] Catalyst

For the first time, microwave (MW) irradiation was successfully applied to peroxidative cyclohexane oxidation catalyzed by a C-scorpionate complex, [FeCl2(Tpm)] (1; Tpm = hydrotris­(pyrazol-1-yl)­methane), providing a highly selective and fast eco-friendly procedure to produce a KA (cyclohexanol + cyclohexanone) oil mixture (up to ca. 100% selectivity) with 28% yield in 1 h at 50 °C in MeCN. Water, organics, and ionic liquids (ILs, [bmim]­[N­(CN)2] and [bmim]­[BF4]) were used as solvents, and their interactions with 1 were determined by DFT calculations. The possibility to recycle and reuse 1 (up to nine consecutive cycles) without loss of activity is also observed for the IL [bmim]­[BF4]. Moreover, higher catalytic activities under additive-free conditions are obtained with the ILs in comparison to those with the other solvents. Tuning the alcohol/ketone selectivity is also possible by choosing the appropriate IL solvent.

本研究首次成功将微波（MW）辐照应用于由C-蝎型配合物[FeCl₂(Tpm)]（1；Tpm=氢三(吡唑-1-基)甲烷）催化的过氧化环己烷氧化反应，开发出一种高选择性、快速且环保的工艺：在50℃、乙腈（MeCN）体系中反应1小时，即可获得产率28%、选择性高达约100%的KA（环己醇与环己酮）油状混合物。本研究以水、有机溶剂以及离子液体（ILs，包括[bmim][N(CN)₂]与[bmim][BF₄]）作为反应溶剂，并通过密度泛函理论（DFT）计算阐明了各溶剂与配合物1之间的相互作用。在以[bmim][BF₄]为溶剂的体系中，配合物1可连续循环回用至多9次且催化活性无衰减。此外，与其他溶剂体系相比，离子液体在无添加剂条件下可展现出更优异的催化活性。通过选用合适的离子液体溶剂，还可灵活调控产物的醇/酮选择性比例。