Guzmán Jefferson, Urriolabeitia Asier, Polo Víctor, Fernández-Buenestado Marta, Iglesias Manuel, Fernández-Alvarez Francisco J
Departamento de Química Inorgánica - Instituto de Síntesis Química y Catálisis Homogénea (ISQCH). Universidad de Zaragoza, Facultad de Ciencias 50009, Zaragoza, Spain.
Departamento de Química Física - Instituto de Biocomputación y Física de Sistemas complejos (BIFI) - Universidad de Zaragoza, Facultad de Ciencias 50009, Zaragoza, Spain.
Dalton Trans. 2022 Mar 15;51(11):4386-4393. doi: 10.1039/d1dt04335h.
Using a low loading of the iridium(III) complexes [Ir(CFSO)(κ-NSi)] (1) (NSi = (4-methylpyridin-2-yloxy)diisopropylsilyl) and [{Ir(κ-NSi)}(μ-CFSO)] (2) (NSi = (4-methylpyridin-2-yloxy)dimethylsilyl) in the presence of EtN, it has been possible to achieve the solventless selective dehydrogenation of formic acid. The best catalytic performance (TOF ≈ 2900 h) has been achieved with 2 (0.1 mol%) and EtN (40 mol% to FA) at 373 K. Kinetic studies at variable temperatures show that the activation energy of the 2-catalyzed process at 353 K is 22.8 ± 0.8 kcal mol. KIE values of 1.33, 2.86, and 3.33 were obtained for the 2-catalyzed dehydrogenation of HCOOD, DCOOH, and DCOOD, respectively, in the presence of 10 mol% of EtN at 353 K. These data show that the activation of the C-H bond of FA is the rate-determining step of the process. A DFT mechanistic study for the catalytic cycle involving hydride abstraction from the formate anion by the metal, assisted by a molecule of formic acid, and heterolytic H formation has been performed. Moreover, the presence of Ir-formate intermediates was identified by means of NMR studies of the catalytic reactions in thf-d at 323 K. In all the cases, the decomposition of the catalyst to give unactive crystalline iridium NPs was observed.
在乙胺存在下,使用低负载量的铱(III)配合物[Ir(CFSO)(κ-NSi)](1)(NSi =(4-甲基吡啶-2-氧基)二异丙基甲硅烷基)和[{Ir(κ-NSi)}(μ-CFSO)](2)(NSi =(4-甲基吡啶-2-氧基)二甲基甲硅烷基),已实现了甲酸的无溶剂选择性脱氢。在373 K下,使用2(0.1 mol%)和乙胺(相对于甲酸为40 mol%)可实现最佳催化性能(TOF≈2900 h⁻¹)。可变温度下的动力学研究表明,在353 K时,2催化过程的活化能为22.8±0.8 kcal mol⁻¹。在353 K下,在10 mol%乙胺存在下,HCOOD、DCOOH和DCOOD的2催化脱氢反应的KIE值分别为1.33、2.86和3.33。这些数据表明,甲酸C-H键的活化是该过程的速率决定步骤。已对催化循环进行了DFT机理研究,该循环包括在甲酸分子的辅助下,金属从甲酸根阴离子中夺取氢化物以及异裂形成H⁺。此外,通过在323 K下对thf-d₈中催化反应的NMR研究确定了Ir-甲酸盐中间体的存在。在所有情况下,均观察到催化剂分解生成无活性的结晶铱纳米颗粒。