Liu Xixi, Han Bo, Wu Chongbei, Zhou Peng, Jia Meilin, Zhu Liangfang, Zhang Zehui
Key Laboratory of Catalysis and Materials Sciences of the Ministry of Education, South-Central Minzu University, Wuhan, 430074, P. R. China.
Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, Sichuan, 610064, PR China.
Angew Chem Int Ed Engl. 2025 Jan 2;64(1):e202413799. doi: 10.1002/anie.202413799. Epub 2024 Nov 2.
Earth-abundant manganese oxides (MnO) were competitive candidates when screening catalysts for ammoxidation of alcohols into nitriles due to their redox property. However, over-oxidation and possible acid-catalyzed hydrolysis of nitriles into amides still limited the application of MnO in nitrile synthesis. In this work, manganese carbodiimide (MnNCN) was first reported to be robust for the ammoxidation of alcohols into nitriles, avoiding over-oxidation and the hydrolysis. Besides the high activity and selectivity, MnNCN demonstrated wide substrate scope including the ammoxidation of primary alcohols into nitriles, the oxidative C-C bonds cleavage and ammoxidation of secondary alcohols, phenyl substituted aliphatic alcohols, and diols into nitriles. Controlled experiments and DFT calculation results revealed that the excellent catalytic performance of MnNCN originated from its high ability in the activation of O molecules, and favorable oxidative dehydrogenation of C=N bonds in the aldimine intermediates (RCH=NH) into nitriles, inhibiting the competitive side reaction of the oxidation of aldehydes into carboxylic acids, followed to amide byproducts. Moreover, the hydrolysis of nitriles was also inhibited over MnNCN for its weak acidity as compared with MnO. This study provided new insights into Mn-catalyzed aerobic oxidations as a highly important complement to manganese oxides.
由于其氧化还原特性，地球上储量丰富的锰氧化物（MnO）在筛选用于将醇氨氧化为腈的催化剂时是具有竞争力的候选材料。然而，过度氧化以及腈可能发生的酸催化水解生成酰胺，仍然限制了MnO在腈合成中的应用。在这项工作中，首次报道了碳二亚胺锰（MnNCN）对醇氨氧化为腈具有很强的活性，避免了过度氧化和水解。除了高活性和选择性外，MnNCN还具有广泛的底物范围，包括将伯醇氨氧化为腈、仲醇、苯基取代的脂肪醇和二醇的氧化C-C键裂解及氨氧化为腈。对照实验和密度泛函理论（DFT）计算结果表明，MnNCN优异的催化性能源于其对O分子的高活化能力，以及对醛亚胺中间体（RCH=NH）中C=N键有利的氧化脱氢生成腈，抑制了醛氧化为羧酸进而生成酰胺副产物的竞争副反应。此外，与MnO相比，MnNCN的酸度较弱，也抑制了腈的水解。这项研究为锰催化的需氧氧化提供了新的见解，作为对锰氧化物的一个非常重要的补充。
