Solvent-Free Microwave-Assisted Peroxidative Oxidation of Alcohols Catalyzed by Iron(III)-TEMPO Catalytic Systems
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The iron(III) complexes [H(EtOH)][FeCl2(L)2] (1), [H2bipy]1/2[FeCl2(L)2].DMF (2) and [FeCl2(L)(2,2′-bipy)] (3) (L = 3-amino-2-pyrazinecarboxylate; H2bipy = doubly protonated 4,4′-bipyridine; 2,2′-bipy = 2,2′-bipyridine, DMF = dimethylformamide) have been synthesized and fully characterized by IR, elemental and single-crystal X-ray diffraction analyses, as well as by electrochemical methods. Complexes 1 and 2 have similar mononuclear structures containing different guest molecules (protonated ethanol for 1 and doubly protonated 4,4′-bipyridine for 2) in their lattices, whereas the complex 3 has one 3-amino-2-pyrazinecarboxylate and a 2,2′-bipyridine ligand. They show a high catalytic activity for the low power (10 W) solvent-free microwave assisted peroxidative oxidation of 1-phenylethanol, leading, in the presence of TEMPO, to quantitative yields of acetophenone [TOFs up to 8.1 × 103 h−1, (3)] after 1 h. Moreover, the catalysts are of easy recovery and reused, at least for four consecutive cycles, maintaining 83 % of the initial activity and concomitant rather high selectivity.
3-Amino-2-pyrazinecarboxylic acid is used to synthesize three new iron(III) complexes which act as heterogeneous catalysts for the solvent-free microwave-assisted peroxidative oxidation of 1-phenylethanol. Open image in new window
KeywordsAlcohol oxidation Mononuclear iron(III) complexes TEMPO Microwave-assisted catalysis
This work has been supported by the Fundação para a Ciência e a Tecnologia (FCT), Portugal (Project UID/QUI/00100/2013). Authors A. Karmakar and S. Hazra express their gratitude to the FCT for post-doctoral fellowships (Ref. Nos. SFRH/BPD/76192/2011 and SFRH/BPD/78264/2011).
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