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Syntheses, Structures, and Catalytic Hydrocarbon Oxidation Properties of N-Heterocycle-Sulfonated Schiff Base Copper(II) Complexes

Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
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Inorganics 2019, 7(2), 17; https://doi.org/10.3390/inorganics7020017
Received: 16 October 2018 / Revised: 3 January 2019 / Accepted: 31 January 2019 / Published: 6 February 2019
(This article belongs to the Special Issue Binuclear Complexes)
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Abstract

Reaction of the o-[(o-hydroxyphenyl)methylideneamino]benzenesulfonic acid (H2L) (1) with CuCl2·2H2O in the presence of pyridine (py) leads to [Cu(L)(py)(EtOH)] (2) which, upon further reaction with 2,2’-bipyridine (bipy), pyrazine (pyr), or piperazine (pip), forms [Cu(L)(bipy)]·MeOH (3), [Cu2(L)2(μ-pyr)(MeOH)2] (4), or [Cu2(L)2(μ-pip)(MeOH)2] (5), respectively. The Schiff base (1) and the metal complexes (25) are stabilized by a number of non-covalent interactions to form interesting H-bonded multidimensional polymeric networks (except 3), such as zigzag 1D chain (in 1), linear 1D chain (in 2), hacksaw double chain 1D (in 4) and 2D motifs (in 5). These copper(II) complexes (25) catalyze the peroxidative oxidation of cyclic hydrocarbons (cyclooctane, cyclohexane, and cyclohexene) to the corresponding products (alcohol and ketone from alkane; alcohols, ketone, and epoxide from alkene), under mild conditions. For the oxidation of cyclooctane with hydrogen peroxide as oxidant, used as a model reaction, the best yields were generally achieved for complex 3 in the absence of any promoter (20%) or in the presence of py or HNO3 (26% or 30%, respectively), whereas 2 displayed the highest catalytic activity in the presence of HNO3 (35%). While the catalytic reactions were significantly faster with py, the best product yields were achieved with the acidic additive. View Full-Text
Keywords: sulfonated Schiff base; copper(II) compounds; pyridine; 2,2’-bipyridine; pyrazine; piperazine; hydrocarbon oxidation sulfonated Schiff base; copper(II) compounds; pyridine; 2,2’-bipyridine; pyrazine; piperazine; hydrocarbon oxidation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Hazra, S.; Rocha, B.G.M.; Guedes da Silva, M.F.C.; Karmakar, A.; Pombeiro, A.J.L. Syntheses, Structures, and Catalytic Hydrocarbon Oxidation Properties of N-Heterocycle-Sulfonated Schiff Base Copper(II) Complexes. Inorganics 2019, 7, 17.

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