Synthesis and Benzene Hydroxylation Properties of Amino Substituted [FeFe]-Hydrogenase Model Compounds
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Synthesis and Benzene Hydroxylation Properties of Amino Substituted [FeFe]‑Hydrogenase Model Compounds Xia Zhang1,3 · Lihong Liu1,2 · Yingzhou Li3 Received: 7 February 2020 / Accepted: 22 March 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Two novel, amino-substituted [FeFe]-hydrogenase model compounds were synthesized and characterized using IR, NMR, mass and UV–Vis spectroscopies as well as elemental analysis. The electrochemical properties (cyclic voltammetry) and catalytic performances of compounds 1 and 2 for the hydroxylation of benzene were investigated. The reduction peaks of compounds 1 and 2 were observed at − 1.93 V, which agrees with the value of the electron density of diiron centers. Compounds 1 and 2 nearly the same electron density around the Fe–Fe bond, but the position of –NH2 group on the pyridine ring largely influenced the stability. Compound 1 demonstrated a higher phenol yield (equal to 12.8%) than compound 2 (10.2%). The biomimetic catalyst formed by the 4-aminopyridine ligand with two iron nuclei, resembling an enzyme active site, had better stability and higher catalytic activity than the 2-aminopyridine derivative. Graphic Abstract Compared the catalytic performance of complexes 1–2, despite 1 and 2 have the same electron density around the Fe–Fe bond, the 4-aminopyridine derivative 1 (12.8%) was more stable and with better catalytic activity compared to 2-aminopyridine derivative 2 (10.2%)
Keywords 4-Aminopyridine · 2-Aminopyridine · [FeFe]-hydrogenase · Hydroxylation
1 Introduction
* Xia Zhang [email protected] Extended author information available on the last page of the article
Phenol is valuable chemical feedstock for synthesis of fibers, resins, antioxidants, synthetic plastics, pharmaceuticals, additives, spices, coatings, dyes, oil refining, and other fine chemicals [1–7]. Currently, the main process for large-scale production of phenol is the cumene (Hock)
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process. Besides phenol, a large amount of acetone is produced in this process. Alternatives to the cumene method are being examined because there has been a movement toward more environmentally friendly, convenient, and efficient syntheses of phenol. In order to address this, methods involving one-step conversion of benzene to phenol are highly desired. The catalytic hydroxylation of benzene at low temperatures has been a topic of interest for many researchers. Several catalysts such as iron complexes, TS-1 zeolites, and Py4PMo11V type composite catalysts have been designed to facilitate the direct hydroxylation of benzene [8–14]. Until now, none of the reported methods have reached industrial scale applications. Iron-based catalysts are the most promising compounds for catalytic oxidation of benzene to phenol due to their low cost, environmental compatibility, low toxicity, high selectivity, and good yields [14]. Biomimetic Fe-based catalysts are especially suitable for selective hydrocarbon oxidation due to their fine-tuned redox states [15–17]. As iron-ba
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