A protocol for solvent-free and additive-free oxidation of primary benzylic C–H bonds with O2 was presented through adjusting the combination of metalloporphyrins and NHPI as binary catalysts to overcome the deficiencies encountered in current oxidation systems. The effects of reaction temperature, porphyrin structure, central metal, catalyst loading and O2 pressure were investigated systematically. For the optimized combination of T(2-OCH3)PPCo and NHPI, all the primary benzylic C–H bonds could be functionalized efficiently and selectively at 120 °C and 1.0 MPa O2 with aromatic acids as the primary products. The selectivity towards aromatic acids could reach up to 70–95% in the conversion of more than 30% for most of the substrates possessing primary benzylic C–H bonds in the metalloporphyrin loading of 0.012% (mol/mol). And the superior performance of T(2-OCH3)PPCo among the metalloporphyrins investigated was mainly attributed to its high efficiency in charge transfer and fewer positive charges around central metal Co (II) which favored the adduction of O2 to cobalt (II) forming the high-valence metal-oxo complex followed by the production of phthalimide N-oxyl radical (PINO) and the initiation of the catalytic oxidation cycle. This work would provide not only an efficient protocol in utilization of hydrocarbons containing primary benzylic C–H bonds, but also a significant reference in the construction of more efficient C–H bonds oxidation systems. The solvent-free and additive-free oxidation of primary benzylic C–H bonds with O2 was presented through adjusting the combination of metalloporphyrins and NHPI as binary catalysts, and the highest selectivity towards aromatic acid reached up to 95.1% with the conversion of 88.5% in the optimized combination of T(2-OCH3)PPCo and NHPI.

中文翻译：

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金属卟啉与 N-羟基邻苯二甲酰亚胺的结合催化 O2 选择性无溶剂和无添加剂氧化初级苄基 C-H 键

通过调整金属卟啉和 NHPI 作为二元催化剂的组合，提出了一种用 O2 无溶剂和无添加剂氧化初级苄基 C-H 键的协议，以克服当前氧化系统中遇到的缺陷。系统研究了反应温度、卟啉结构、中心金属、催化剂负载量和O2压力的影响。对于 T(2-OCH3)PPCo 和 NHPI 的优化组合，所有主要的苄基 C-H 键都可以在 120°C 和 1.0 MPa O2 下以芳香酸为主要产物有效和选择性地官能化。对于大多数在金属卟啉负载为 0.012% (mol/mol) 中具有初级苄基 C-H 键的底物，对芳香酸的选择性可高达 70-95%，转化率超过 30%。在所研究的金属卟啉中，T(2-OCH3)PPCo 的优异性能主要归因于其电荷转移效率高和中心金属 Co (II) 周围的正电荷较少，这有利于 O2 与钴 (II) 的加成形成高价金属-氧配合物，随后产生邻苯二甲酰亚胺 N-氧基自由基（PINO）并引发催化氧化循环。这项工作不仅为利用含初级苄基 C-H 键的碳氢化合物提供了有效的方案，而且为构建更有效的 C-H 键氧化系统提供了重要参考。通过调节金属卟啉和 NHPI 作为二元催化剂的组合，提出了无溶剂和无添加剂氧化初级苄基 C-H 键与 O2，