Synthesis, Structures, Electrochemistry, and Catalytic Activity towards Cyclohexanol Oxidation of Mono-, Di-, and Polynuclear Iron(III) Complexes with 3-Amino-2-Pyrazinecarboxylate

Anirban Karmakar,Luísa M.D.R.S Martins,Armando J L Pombeiro,Yuliya Yahorava,M Fátima C Guedes Da Silva

doi:10.3390/app10082692

Anirban Karmakar, Luísa M.D.R.S Martins + Show 3 more

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https://doi.org/10.3390/app10082692

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Abstract

The synthesis and characterization of a set of iron(III) complexes, viz. the mononuclear [Fe(L)3] (1) and [NHEt3][Fe(L)2(Cl)2] (2), the dinuclear methoxido-bridged [Fe(L)2(μ-OMe)]2.DMF.1.5MeOH (3), and the heteronuclear Fe(III)/Na(I) two-dimensional coordination polymer [Fe(N3)(μ-L)2(μ-O)1/2(Na)(μ-H2O)1/2]n (4), are reported. Reactions of 3-amino-2-pyrazinecarboxylic acid (HL) with iron(III) chloride under different reaction conditions were studied, and the obtained compounds were characterized by elemental analysis, Fourier Transform Infrared (FT-IR) spectroscopy, and X-ray single-crystal diffraction. Compound 1 is a neutral mononuclear complex, whereas 2 is mono-anionic with its charge being neutralized by triethylammonium cation. Compounds 3 and 4 display a di-methoxido-bridged dinuclear complex and a two-dimensional heterometallic Fe(III)/Na(I) polynuclear coordination polymer, respectively. Compounds 3 and 4 are the first examples of methoxido- and oxido-bridged iron(III) complexes, respectively, with 3-amino-2-pyrazinecarboxylate ligands. The electrochemical study of these compounds reveals a facile single-electron reversible Fe(III)-to-Fe(II) reduction at a positive potential of 0.08V vs. saturated calomel electrode (SCE), which is in line with their ability to act as efficient oxidants and heterogeneous catalysts for the solvent-free microwave-assisted peroxidative oxidation (with tert-butyl hydroperoxide) of cyclohexanol to cyclohexanone (almost quantitative yields after 1 h). Moreover, the catalysts are easily recovered and reused for five consecutive cycles, maintaining a high activity and selectivity.

Highlights

The coordination chemistry of iron(III) compounds with oxido-bridged species is valuable to synthetic chemists [1] namely due of their applications in biological systems, such as in storage and transport of dioxygen [2], phosphate ester hydrolysis [3], DNA synthesis [4], etc
Iron(III) complexes or coordination polymers have been reported by various research groups, which show interesting applications in areas of magnetism, catalysis, biology, electrochemistry, etc. [11]
The solvothermal reaction of of HL with FeCl3 .6H2 O in the presence of NaN3 in DMF and methanol mixture leads to the HL with FeCl3.6H2O in the presence of NaN3 in DMF and methanol mixture leads to the formation of formation of the oxido- andheterometallic aqua-bridgedFe(III)/Na(I)

Summary

Introduction

The coordination chemistry of iron(III) compounds with oxido-bridged species is valuable to synthetic chemists [1] namely due of their applications in biological systems, such as in storage and transport of dioxygen [2], phosphate ester hydrolysis [3], DNA synthesis [4], etc. Oxido-bridged dinuclear iron(III) units are present at the active site of various non-heme metalloenzymes, such as hemerythrin, methane monooxygenase (MMO), ribonucleotide reductase, etc. Several oxido- [6], hydroxido- [7], alkoxido- [8], peroxido- [9], or carboxylato-bridged [10]. Iron(III) complexes or coordination polymers have been reported by various research groups, which show interesting applications in areas of magnetism, catalysis, biology, electrochemistry, etc.

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