cyclohexane oxidation in homogeneous and carbon-supported catalysis

The authors are grateful for the Financial support from Fundação para a Ciência e a Tecnologia (FCT), Portugal, through project UIDB/00100/2020 of Centro de Quίmica Estrutural. The work was also funded by national funds through FCT, under the Scientific Employment Stimulus-Institutional Call (CEEC-INST/00102/2018). We also acknowledge the Associate Laboratory for Green Chemistry – LAQV financed by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/5006/2020) and Base-UIDB/50020/ 2020 and Programmatic-UIDP/50020/2020 funding of the Associate Laboratory LSRE-LCM. I. L. L. acknowledges the CATSUS Ph.D. Program from FCT for her grant PD/BD/135555/2018. A. P. is grateful to FCT and Instituto Superior Técnico (IST), Portugal through DL/57/2017 (Contract no. IST-ID/197/2019). AGM is grateful to Associação do Instituto Superior Técnico para Investigação e Desenvolvimento for his post-doctoral fellowship through grant no. BL133/2021-IST-ID. This publication is also supported by the RUDN University Strategic Academic Leadership Program (recipient AJLP, preparation). A. V. G. thanks FCT, Instituto Superior Técnico (DL 57/2016, L 57/2017 and CEEC Institutional 2018 Programs, Contract no: IST-ID/110/2018) and Baku State University for financial support. The authors also acknowledge the Portuguese NMR Network (IST-UL Centre) for access to the NMR facility. CFGCG thanks the FCT for funding the Coimbra Chemistry Centre through the programmes UIDB/00313/2020 and UIDP/00313/2020, also co-founded by FEDER/ COMPETE 2020-EU. The authors are also thankful to Benjoe Rey B. Visayas (University of Massachusetts Dartmouth) for the help with the graphics.In accordance with UN's Sustainable Development Goal (UN's SDG) 12 which encompasses the sustainable use of chemical products and a sound circular economy, this work is focused on the synthesis of Co(II), Ni(II) and Mn(II) complexes bearing combined 1,3,5-triaza-7-phosphaadamantane and benzyl terpyridine core moieties (PTA–Bztpy) as ligand, followed by their evaluation as catalysts for the microwave-assisted cyclohexane oxidation using tert-butyl hydroperoxide (TBHP) as oxidant. The most active catalyst, with a manganese metal center, was heterogenized on six different carbon materials. The results disclosed the influence of several reaction parameters, such as catalyst loading, temperature, reaction time and solvent, on the catalytic activity and selectivity of the homogeneous and carbon-supported catalysts. Recyclability of the carbon-supported catalyst allowed facile separations, recovery and reuse for five consecutive cycles.publishersversionpublishe

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Chalcogen bonding in coordination chemistry

The chalcogen bond (ChB) is defined as a noncovalent interaction between the electron density deficient region (so-called as sigma or pi hole) of a covalently bonded chalcogen atom and a nucleophilic (Nu) site in the same (intramolecular) or another (intermolecular) molecular entity: R-Ch center dot center dot center dot Nu [Ch = O, S, Se or Te; R = C, Pn (pnictogen), Ch, metal, etc.; Nu = lone pair possessing Ha, Ch, Pn or metal atom, pi-system, anion, radical, etc.]. Like in halogen (Ha) and pnictogen (Pn) bonds, the bond parameters (strength, high directionality and tunability) make ChB a relevant supramolecular tool in the design of the secondary coordination sphere of metal complexes, which concerns an important synthetic strategy in the improvement of functional properties of materials. In this review we discuss/illustrate several relevant examples, taken from the Cambridge Structural Database, in which ChB plays a crucial role in the decoration of the secondary coordination sphere of coordination compounds, controlling molecular conformation, packing and aggregation of tectons, as well as formation of supramolecular 0D aggregates, 1D chains, 2D layers, 3D frameworks, etc.(c) 2022 Elsevier B.V. All rights reserved

Peroxidative Oxidation of Cyclohexane Using 3d Metal Complexes with Hydrazone-Derived Ligands as Catalysts: Exploring (Un)Conventional Conditions

Two tetranuclear and two mononuclear Cu(II) complexes with arylhydrazones of malononitrile derived ligands (compounds 1–2 and 3–4, respectively), one trinuclear Co(II/III) complex with an arylhydrazone of acetoacetanilide (5) and one tetranuclear Zn(II) complex of 3-(2-carboxyphenyl-hydrazone)pentane-2,4-dione (6) were screened as potential catalysts in the peroxidative oxidation of cyclohexane by aqueous H2O2 in acetonitrile. The best results were attained in the presence of pyrazine-2-carboxylic acid (PCA) with 1 (26% yield, TON = 52.0) and with 2 (24%, TON = 48.0) after 4 h at 40 °C. In the presence of complexes 5 and 6, no oxygenated products were detected in the studied conditions. The employment of non-conventional conditions like supercritical carbon dioxide (scCO2) as reaction medium or microwave (MW) irradiation was assessed for complexes 1 and 2. After 6 h in acetonitrile–scCO2, at 50 °C and with HNO3 as promoter, only 17% yield was achieved using 1 as catalyst, and 21% using 2. Total yields of oxygenates up to 14 (with 1) and 13% (2) and TOFs of 56.0 and 52.0 h−1, respectively, were obtained working under MW irradiation at 70 °C and for the much shorter time of 0.5 h

Tetrel, Chalcogen, and Charge-Assisted Hydrogen Bonds in 2-((2-Carboxy-1-(substituted)-2-hydroxyethyl)thio) Pyridin-1-ium Chlorides

Reaction of 2-chloro-2-(diethoxymethyl)-3-substitutedoxirane or 1-chloro-1-(substituted) -3,3-diethoxypropan-2-one with pyridine-2-thiol in EtOH at 25 °C yields 3-(diethoxymethyl)-3-hydroxy-2-substituted-2,3-dihydrothiazolo[3,2-a]pyridin-4-ium chlorides, which subsequently, in MeCN at 85°C, transforms into ring-opening products, 2-((2-carboxy-1-(substituted) -2-hydroxyethyl)thio)pyridin-1-ium chlorides. The tetrel (C···O) and chalcogen (S···O) bonds are found in the structures of 5 and 6, respectively. Compound 6 is also present in halogen bonding with a short O···Cl distance (3.067 Å). Both molecules are stabilized in crystal by tetrel, chalcogen, and multiple charge-assisted hydrogen bonds