Adomeit Sven, Rabeah Jabor, Surkus Annette E, Bentrup Ursula, Brückner Angelika
Leibniz-Institut für Katalyse, Universität Rostock , Albert-Einstein Straße 29A, 18059 Rostock, Germany.
Inorg Chem. 2017 Jan 3;56(1):684-691. doi: 10.1021/acs.inorgchem.6b02925. Epub 2016 Dec 21.
Selective aerobic oxidation of benzyl alcohol to benzaldehyde by a (bpy)Cu(IM)/TEMPO catalyst (IM represents differently substituted imidazoles) has been studied by simultaneous operando electron paramagnetic resonance/UV-vis/attentuated total reflectance infrared spectroscopy in combination with cyclic voltammetry to explore the particular role of imidazole in terms of ligand and/or base as well as of its substitution pattern on the catalytic performance. For molar ratios of IM/Cu ≥ 2, a (bpy)Cu(IM)(IM) complex is formed, in which the Cu-N distances and/or angles for the two IM ligands a and b are different. The coordination of a second IM molecule boosts the oxidation of Cu to Cu and, thus, helps to activate O by electron transfer from Cu to O. The rates of Cu oxidation and Cu reduction and, thus, the rates of benzaldehyde formation depend on R of the R-N moiety in the IM ligand. Oxidation is fastest for R = H and alkyl, while reduction is slowest for R = H. The Cu/Cu interplay leads to decreasing total benzaldehyde formation rates in the order R (I+ effect) > R (conjugated system) > R = H.
通过同步操作电子顺磁共振/紫外可见/衰减全反射红外光谱结合循环伏安法，研究了(bpy)Cu(IM)/TEMPO催化剂（IM代表不同取代的咪唑）将苯甲醇选择性有氧氧化为苯甲醛的过程，以探讨咪唑在配体和/或碱方面的特殊作用及其取代模式对催化性能的影响。当IM/Cu的摩尔比≥2时，会形成一种(bpy)Cu(IM)(IM)配合物，其中两个IM配体a和b的Cu-N距离和/或角度不同。第二个IM分子的配位促进了Cu氧化为Cu，从而通过从Cu到O的电子转移有助于激活O。Cu氧化和Cu还原的速率，进而苯甲醛形成的速率取决于IM配体中R-N部分的R。对于R = H和烷基，氧化最快，而对于R = H，还原最慢。Cu/Cu相互作用导致苯甲醛总生成速率按R（I+效应）> R（共轭体系）> R = H的顺序降低。
