Béres Kende Attila, Homonnay Zoltán, Kvitek Libor, Dürvanger Zsolt, Kubikova Martina, Harmat Veronika, Szilágyi Fanni, Czégény Zsuzsanna, Németh Péter, Bereczki Laura, Petruševski Vladimir M, Pápai Mátyás, Farkas Attila, Kótai László
Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar Tudósok krt. 2, H-1117 Budapest, Hungary.
György Hevesy PhD School of Chemistry, Institute of Chemistry, ELTE Eötvös Loránd University, Pázmány Péter s. 1/A, H-1117 Budapest, Hungary.
Inorg Chem. 2022 Sep 12;61(36):14403-14418. doi: 10.1021/acs.inorgchem.2c02265. Epub 2022 Aug 31.
Research on new reaction routes and precursors to prepare catalysts for CO hydrogenation has enormous importance. Here, we report on the preparation of the permanganate salt of the urea-coordinated iron(III), [hexakis(urea-)iron(III)]permanganate (Fe(urea-O)) via an affordable synthesis route and preliminarily demonstrate the catalytic activity of its (Fe,Mn)O thermal decomposition products in CO hydrogenation. Fe(urea-O) contains O-coordinated urea ligands in octahedral propeller-like arrangement around the Fe cation. There are extended hydrogen bond interactions between the permanganate ions and the hydrogen atoms of the urea ligands. These hydrogen bonds serve as reaction centers and have unique roles in the solid-phase quasi-intramolecular redox reaction of the urea ligand and the permanganate anion below the temperature of ligand loss of the complex cation. The decomposition mechanism of the urea ligand (ammonia elimination with the formation of isocyanuric acid and biuret) has been clarified. In an inert atmosphere, the final thermal decomposition product was manganese-containing wuestite, (Fe,Mn)O, at 800 °C, whereas in ambient air, two types of bixbyite (Fe,Mn)O as well as jacobsite (Fe,Mn)(Fe,Mn)O), with overall Fe to Mn stoichiometry of 1:3, were formed. These final products were obtained regardless of the different atmospheres applied during thermal treatments up to 350 °C. Disordered bixbyite formed first with inhomogeneous Fe and Mn distribution and double-size supercell and then transformed gradually into common bixbyite with regular structure (and with 1:3 Fe to Mn ratio) upon increasing the temperature and heating time. The (Fe,Mn)O intermediates formed under various conditions showed catalytic effect in the CO hydrogenation reaction with <57.6% CO conversions and <39.3% hydrocarbon yields. As a mild solid-phase oxidant, hexakis(urea-)iron(III) permanganate, was found to be selective in the transformation of (un)substituted benzylic alcohols into benzaldehydes and benzonitriles.
研究用于CO加氢的新型反应路线和前驱体制备催化剂具有极其重要的意义。在此，我们报道了通过一种经济实惠的合成路线制备尿素配位铁(III)的高锰酸盐，即[六(尿素)铁(III)]高锰酸盐(Fe(尿素-O))，并初步证明了其(Fe,Mn)O热分解产物在CO加氢反应中的催化活性。Fe(尿素-O)在Fe阳离子周围呈八面体螺旋状排列，含有O配位的尿素配体。高锰酸根离子与尿素配体的氢原子之间存在广泛的氢键相互作用。这些氢键作为反应中心，在配合物阳离子配体损失温度以下尿素配体与高锰酸根阴离子的固相聚分子内氧化还原反应中发挥独特作用。已阐明尿素配体的分解机理（氨消除并形成异氰尿酸和缩二脲）。在惰性气氛中，800℃时最终热分解产物为含锰的方铁矿(Fe,Mn)O，而在环境空气中，形成了两种类型的方铁锰矿(Fe,Mn)O以及锰铁尖晶石(Fe,Mn)(Fe,Mn)O)，Fe与Mn的总化学计量比为1:3。无论在高达350℃的热处理过程中采用何种不同气氛，均可获得这些最终产物。无序方铁锰矿首先形成，其Fe和Mn分布不均匀且具有双倍尺寸的超晶胞，然后随着温度和加热时间的增加逐渐转变为结构规则（Fe与Mn比例为1:3）的普通方铁锰矿。在各种条件下形成的(Fe,Mn)O中间体在CO加氢反应中表现出催化作用，CO转化率<57.6%，烃产率<39.3%。作为一种温和的固相氧化剂，六(尿素)铁(III)高锰酸盐被发现对（未）取代的苄醇转化为苯甲醛和苄腈具有选择性。
