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Iron-containing particulate catalysts of 0.1&ndash, 1 &micro, m size were prepared by wet and ball-milling procedures from common salts and characterized by FTIR, TGA, UV-Vis, PXRD, FEG-SEM, and XPS analyses. It was found that when the wet method was used, semi-spherical magnetic nanoparticles were formed, whereas the mechanochemical method resulted in the formation of nonmagnetic microscale needles and rectangles. Catalytic activity of the prepared materials in the oxidation of 1-phenylethanol to acetophenone was assessed under conventional heating, microwave (MW) irradiation, ultrasound (US), and oscillating magnetic field of high frequency (induction heating). In general, the catalysts obtained by wet methods exhibit lower activities, whereas the materials prepared by ball milling afford better acetophenone yields (up to 83%). A significant increase in yield (up to 4 times) was observed under the induction heating if compared to conventional heating. The study demonstrated that MW, US irradiations, and induction heating may have great potential as alternative ways to activate the catalytic system for alcohol oxidation. The possibility of the synthesized material to be magnetically recoverable has been also verified.

A series of phthalocyanine (Pc) complexes of general formula [M(Pc)] (M = Mg, V, Mn, Fe, Co, Ni, Cu, Zn) was tested as catalysts for functionalization of sp3 C H bonds, namely in the mild stereoselective oxidation of cyclic alkanes (isomers of dimethylcyclohexane and decahydronaphthalene) using peroxides as oxidants. A high catalytic activity (yield of products up to 75% based on the oxidant) and outstanding retention of stereoconfiguration of substrates (>95% for isomers of dimethylcyclohexane) was disclosed for the cobalt phthalocyanine catalyst [Co(Pc)] using m-chloroperbenzoic acid (m-CPBA) as oxidant and nitric acid as promoter. The phthalocyanine complexes other than Co are much less active with yields of products

A series of known metal complexes, [LaL2(NO3)(H2O)2]·5H2O (1), [Zn(μ-L)(NO3)(H2O)]n (2), {[Cd2(μ-HL)(μ-L)(NO3)3(H2O)]·H2O}n (3) and [Hg(μ-L)(N3)]n·nH2O (4), were synthesized from the corresponding metal salts and 2-pyridinecarboxaldehyde isonicotinoylhydrazone (HL), and demonstrated high activity and selectivity in the cyanosilylation of aldehydes. Although all the complexes are derived from the same HL hydrazone ligand, the catalytic activity of 1–4 is different and relates to the metal center and coordination environment, whereas complex 1 being the most effective homogeneous Lewis acid-base catalyst towards the synthesis of cyanohydrin trimethylsilyl ethers from both aliphatic and aromatic aldehydes with yields up to 96.3 % in 6 h in methanol solution and at room temperature. According to the proposed mechanism, both coordination and noncovalent interactions (hydrogen and tetrel bonds) play a significant role and account for the higher catalytic activity of complex 1.

This review describes how non-covalent interactions, such as hydrogen (inter- and intramolecular, resonance- and charge-assisted hydrogen bonding), halogen, chalcogen and pnicogen bonds, π-interactions, as well as other types of weak forces can influence and control the reactions in the synthesis, e.g., of metal-containing supramolecular networks, providing a class of highly directional stabilizing contacts that can be exploited in the design of coordination compounds. The selected recent examples show that both inter- and intramolecular non-covalent interactions can influence the formation of coordination compounds. This overview of non-covalent interactions applied for synthesis and design of coordination compounds also contributes to an improved understanding of their behavior in crystal engineering, catalysis, etc. It provides a practical consultation for synthetic chemists that are interested in exploring and further developing non-covalent interactions assisted synthesis and design of coordination compounds.

Thiadiazoles are among the privileged pharmacological building blocks due to their unique chemical properties for diverse biological and clinical applications. 1,2,4-Thiadiazole derivatives have recently attained a therapeutic and economic importance that they did not possess a few years ago, thus leading to growing interest in this class of heterocycles. Moreover, the importance of such molecules is not restricted to medicinal chemistry; they also perform well as N,S ligands in coordination chemistry or as important intermediates for fine-chemicals synthesis. In this context, this review systematizes the main advances in the synthesis of 1,2,4-thiadiazole-based compounds in the last ten years and discloses some relevant applications of these compounds during that period.

The new 1D copper(II) coordination polymers (CPs) [Cu(μ-L1)(H2O)]n (1, H2L1 = 2-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl)benzoic acid) and [Cu(μ-H2L2)(H2O)]n (2, H4L2 = (Z)-2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazinyl)terephthalic acid) and the known zwitterionic 1D CP [Cu2(H2O)2(μ-H2L3)(μ-L3)]n (3, H3L3 = 2-(2-(4,4-dimethyl-2,6-dioxocyclo-hexylidene)hydrazinyl)terephthalic acid) were synthesized and tested as homogeneous catalysts for cyanosilylation of a variety of aldehydes to the corresponding cyanohydrin trimethylsilyl ethers. Among these polymeric catalysts, 3, with a zwitterionic charater, is the most effective one, giving 86–99% yield of the ethers upon reaction of aliphatic and aromatic aldehydes with trimethylsilyl cyanide in methanol at room temperature in 4 h. Non-covalent interactions (cation-π and tetrel bondings) involving the aldehyde substrate are proposed to assist the cyanosilylation reaction.

Sodium 2-(2-(1-cyano-2-oxopropylidene)hydrazinyl)benzenesulfonate (NaHL) was synthesized by azocoupling of diazonium salt of 2-aminobenzenesulfonic acid with 3-oxobutanenitrile and characterized by IR, 1H and 13C NMR spectroscopies and ESI-MS analysis. In dimethylsulfoxide-d6 solution NaHL exists as a mixture of Z- and E-hydrazone forms in the amounts of 96 and 4%, respectively. Treatment of this isomeric mixture with copper(II) nitrate hydrate in the presence of ethylenediamine (en) provides unusual (E,Z) → E switching of NaHL to give [Cu(H2O)2(en)2](HL)2 (1). The process is interpreted on the basis of cooperative ionic interactions and resonance assisted hydrogen bonding (RAHB) → charge assisted hydrogen bonding (CAHB) transition.

Three new water-soluble copper(II) complexes [Cu(HL)(H2O){(CH3)2NCHO}] (1), [Cu(H2L)2(im)4]·CH3OH (2) and [Cu(HL)(CH3OH)]2(μ2-py) (3) were synthesized from copper(II) nitrate and sodium (Z)-2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazinyl)benzene-sulfonate (NaH2L), in the absence (for 1) and presence of imidazole (im) (for 2) or pyrazine (py) (for 3), and fully characterized. The complexes 1–3 have been tested as stereoselective C H activating catalysts for the model nitroaldol (Henry) condensation of nitroethane with various aldehydes in water. 1 was the most active catalyst affording 64−87% yields with syn/anti diasteroselectivities up to 77:23.

Heterometallic double Fe2O3–CoCl2, CoCl2–V2O5, MoO3–V2O5, and triple CuO–Fe2O3–CoCl2 3d metal dispersed systems were easily prepared by ball milling at room temperature and characterized by scanning electron microscopy (SEM), field emission gun scanning electron microscopy (FEGSEM), energydispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). They catalyze the microwave-assisted solvent-free heterogeneous oxidation of 1-phenylethanol to acetophenone with tert-butyl hydroperoxide (t-BuOOH) as oxidant, used as a model reaction. In most of the heterometallic systems a significant improvement in the catalytic activity was observed in comparison to homometallic ones. For the tested catalytic systems and experimental conditions, the CuO–Fe2O3–CoCl2 and Fe2O3–CoCl2 systems exhibit the highest activity with maximum 78% yield and TON 39 after 1 h. The possibility of magnetic recovery of the catalysts was demonstrated for the Fe2O3–CoCl2 (3:1) system. info:eu-repo/semantics/publishedVersion

Chalcogen bonding is a type of noncovalent interaction in which a covalently bonded chalcogen atom (O, S, Se or Te) acts as an electrophilic species towards a nucleophilic (negative) region(s) in another or in the same molecule. In general, this interaction is strengthened by the presence of an electron-withdrawing group on the electron-acceptor chalcogen atom and upon moving down in the periodic table of elements, from O to Te. Following a short discussion of the phenomenon of chalcogen bonding, this Perspective presents some demonstrative experimental observations in which this bonding is crucial for synthetic transformations, crystal engineering, catalysis and design of materials as synthons/tectons.

3d metal (Cu, Fe, Co, V) containing composite catalysts for the solvent-free microwave-assisted transformation of 1-phenylethanol to acetophenone with tert-butyl hydroperoxide (TBHP) as oxidant were prepared by ball milling. The influence of multiwalled carbon nanotubes (CNTs) and graphene oxide (GO) additives on the catalytic activity of the catalysts was studied. CNTs or GO were mixed by ball milling with the metal salts (CoCl2), oxides (CuO, Fe2O3, V2O5) or binary systems (Fe2O3-CoCl2, CoCl2-V2O5, CuO-Fe2O3). For CoCl2-based catalytic systems, addition of small amounts (0.1–5%) of CNTs or GO leads to significant improvement in catalytic activity, e.g. 1% of the CNTs additive allows to rise yields from 28 to 77%, under the same catalytic conditions. The CoCl2-5%CNTs composite is the most active among the studied ones with 85% yield and TON of 43 after 1 h.

The mononuclear copper complexes [Cu{NH=C(OR)NC(OR)=NH}2] with alkoxy-1,3,5-triazapentadiene ligands that have different substituents (R = Me (1), Et (2), nPr (3), iPr (4), CH2CH2OCH3 (5)) were prepared, characterized (including the single crystal X-ray analysis of 3) and studied as catalysts in the mild oxidation of alkanes with H2O2 as an oxidant, pyridine as a promoting agent and cyclohexane as a main model substrate. The complex 4 showed the highest activity with a yield of products up to 18.5% and turnover frequency (TOF) up to 41 h&minus, 1. Cyclohexyl hydroperoxide was the main reaction product in all cases. Selectivity parameters in the oxidation of substituted cyclohexanes and adamantane disclosed a dominant free radical reaction mechanism with hydroxyl radicals as C&ndash, H-attacking species. The main overoxidation product was 6-hydroxyhexanoic acid, suggesting the presence of a secondary reaction mechanism of a different type. All complexes undergo gradual alteration of their structures in acetonitrile solutions to produce catalytically-active intermediates, as evidenced by UV/Vis spectroscopy and kinetic studies. Complex 4, having tertiary C&ndash, H bonds in its iPr substituents, showed the fastest alteration rate, which can be significantly suppressed by using the CD3CN solvent instead of CH3CN one. The observed process was associated to an autocatalytic oxidation of the alkoxy-1,3,5-triazapentadiene ligand. The deuterated complex 4-d32 was prepared and showed higher stability under the same conditions. The complexes 1 and 4 showed different reactivity in the formation of H218O from 18O2 in acetonitrile solutions.

Chemical transformations induced by mechanical force in solids are remarkable since they facilitate syntheses that are normally difficult to achieve in solution and thus allow the preparation of new molecules and materials or drastic improvements of the yields and selectivities. In many cases, the noncovalent interactions (NCIs) with mechanochemical treatment differ significantly from those which occur in analogous solvent-assisted processes. Moreover, if a “mechanocatalyst” is introduced into the system, it can additionally alter the NCIs, bond energies and properties of the reaction intermediates. As result, the outcome of many mechanocatalytic reactions can be very different in terms of efficiency or even reaction pathways compared with the traditional solution-based procedures or noncatalytic mechanochemical processes. Accordingly, in this chapter, certain mechanocatalytic reactions in which the NCIs play a key role are overviewed and discussed. Additionally, an overview of some experimental techniques used to study mechanochemical activation and the respective NCIs is also provided.

Intensification of chemical processes according to the motto “faster, simpler, greener” is among the main concerns nowadays. One of the ways of intensification is the application of synergistic catalytic effects when the overall efficiency of a composite catalyst is much higher than the sum of the component activities. Here, we report on the preparation of synergistic catalytic materials by a simple and straightforward ball milling procedure. Oxidation of benzoin was selected as a model reaction to demonstrate the viability of the concept. For the V2O5–TiO2 (95 : 5) composite material, the synergistic effect is triggered by low power microwave irradiation with more than a tenfold jump in the catalytic activity in comparison to the activities of the individual components.

In this review we attempted to answer the question: how to construct complex functionalized molecules with significant added value from cheap and readily available alcohols in the simplest and most efficient manner? Accordingly, recent developments (mainly from the last 5 years) in the field of one-pot multiple transformations of alcohols are overviewed in terms of the process simplification and optimization, sustainability, atom-, bond-, step- and redox- economy. A particular attention has been paid to chemo- and stereoselective transformations with specific formation of particular bonds and configurations, leaving other parts of substrates unchanged.

Thiazole derived compounds have great potential in medicinal- and agro-chemistries, catalysis, cosmetic industry, corrosion protection, light harvesting, production of light-emitting diodes (LEDs), photochromes and molecular switches or nonlinear optical materials. In spite of that, not much attention has been paid to the coordination chemistry of this class of versatile and polyfunctional heterocyclic ligands. This review intends to systematize the existing information in this field and to highlight some perspectives in the synthesis and applications of 1,3-thiazole, isothiazole and thiadiazole metal complexes.

Two complexes with isoindole-core ligands of general formula [M{C6H4C(NH2)NC(ONCMe2)2}2](NO3)2 (M = Co for 1 and M = Ni for 2) were studied as catalysts for the mild stereoselective alkane oxidation with m-chloroperbenzoic acid (m-CPBA) as an oxidant and cis-1,2-dimethylcyclohexane (cis-1,2-DMCH) as a main model substrate. Complex 1 disclosed a pronounced activity, with high retention of stereoconfiguration of substrates (>98% for cis-1,2-DMCH) and highest cis/trans ratio of tertiary alcohols (products) of 56, under mild conditions. The best achieved yields of tertiary cis-alcohols were of 13.7 and 50.5%, based on the substrate (cis-1,2-DMCH) and the oxidant (m-CPBA) respectively. Kinetic experiments, high bond and stereoselectivity parameters, kinetic isotope effect of 7.2(2) in the oxidation of cyclohexane, and incorporation of 18O from H218O support the involvement of CoIVO high-valent metal–oxo intermediates as main C–H attacking species.

Este trabalho foi financiado pelo Concurso Anual para Projetos de Investigação, Desenvolvimento, Inovação e Criação Artística (IDI&CA) 2016 do Instituto Politécnico de Lisboa. Código de referência IPL/2016/MechSynCat_ISEL The effect of microwave and mechanochemical ball milling energy inputs was studied for the peroxidative oxidation (with aqueous H2O2) of cyclohexane to cyclohexanol and cyclohexanone, over CoCl2 and/or V2O5 dispersed (μm scale) catalysts. A maximum total yield of cyclohexanol and cyclohexanone of 43% after 1 h of reaction at 30 °C, in acetonitrile and under microwave irradiation (5 W), was achieved over the CoCl2–V2O5 (3 : 1) catalyst prepared by ball milling. Cyclohexanol is the main final product with a selectivity of up to 93% over cyclohexanone. Conducting the oxidation reaction under microwave irradiation under the same conditions but without any mechanochemical treatment of the catalyst prior to use resulted in a lower total yield of 30% with a lower selectivity (69%) towards cyclohexanol over cyclohexanone. The sole application of mechanochemical treatment for the catalyst preparation and the catalytic oxidation of cyclohexane allowed to reach yields of 29% after 1 h of reaction, at room temperature, without microwave irradiation and any additive and in the absence of any organic solvent. Ball milling is shown to provide a convenient, solvent-free method to disperse these solid catalysts and to promote the above cyclohexane oxidation, although, in the latter case, not so effectively as microwave irradiation. info:eu-repo/semantics/publishedVersion

A new catalytic system for the anaerobic oxidation of benzyl alcohols using a tetrazole-amino-saccharin organocatalyst has been established. In a solvent-free and microwave assisted process comprising aqueous tert-butyl hydroperoxide (TBHP) as oxidant, a variety of benzyl alcohols has been efficiently converted to aldehydes under mild conditions. Most reactions are complete within 30 min and the catalyst exhibits varied functional group compatibility. A catalytic cycle for the oxidation of the alcohols promoted by the tetrazole-amino-saccharin derivative is outlined involving radical species. DFT calculations performed for the oxidation of benzyl alcohol with and without organocatalyst show that the rate limiting step of the whole reaction is the cleavage of the O-O bond in TBHP with the subsequent hydrogen abstraction from the alcohol. The tetrazole-amino-saccharin organocatalyst assists the H-abstraction from benzyl alcohol by the bound HO center dot radical. The simplicity, selectivity and softness of reaction conditions of the studied organocatalytic protocol suggest a great potential for extensive use in synthetic chemistry. (C) 2017 Elsevier B.V. All rights reserved. Foundation for Science and Technology (FCT), Portugal [IF/01270/2013/CP1163/CT0007] FCT [SFRH/BPD/99851/2014, SFRH/BD/52370/2013, PD/00248/2012]

A series of soluble in common organic solvents nickel(II) 14,28-dialkoxy-substituted phthalocyanines is synthesized by reaction of nickel acetate tetrahydrate with 1,2-dicyanobenzene in the presence of an alcohol under solvothermal conditions. Single crystal X-ray diffraction analyses reveal that the two alkoxy groups are added in a syn-conformation mode in all the studied cases. The use of microwave irradiation leads to decomposition of the nickel(II) 14,28-dialkoxy-substituted phthalocyanines.

Mononuclear Cu(II) and Co(II) complexes comprising 2-methyltetrazole-saccharinate bidentate N,N-chelating ligand have been synthesized for the first time and tested as homogeneous catalysts for oxidation of secondary alcohols in a solvent-free and microwave assisted protocol using aqueous tertbutyl hydroperoxide (TBHP) as oxidant. The developed catalytic system exhibits broad functional group compatibility, allowing efficient and selective conversion of a variety of secondary alcohols, including allylic ones, into the corresponding ketones. With typical 0.2 mol% content of the catalyst and under 20-50 W microwave irradiation, most reactions are complete within 10 min, presenting TONs up to 5.5 x 10(2) and TOFs up to 1.1 x 10(4)h(-1). No additives and co-oxidants have been used, while TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxyl) acts as inhibitor in most cases. A plausible reaction mechanism involving the new catalytic systems is outlined. (C) 2016 Elsevier B.V. All rights reserved.

This review concerns metal-catalyzed reactions of oxidation of alcohols to the respective products, mainly ketones and aldehydes, mostly within the period of 2010–2014. Both conventional and unconventional systems, not only with usual reagents, but also with uncommon and prospective ones, are overviewed, with recently achieved developments.

Thiazole derived compounds have great potential in medicinal- and agro-chemistries, catalysis, cosmetic industry, corrosion protection, light harvesting, production of light-emitting diodes (LEDs), photochromes and molecular switches or nonlinear optical materials. In spite of that, not much attention has been paid to the coordination chemistry of this class of versatile and polyfunctional heterocyclic ligands. This review intends to systematize the existing information in this field and to highlight some perspectives in the synthesis and applications of 1,3-thiazole, isothiazole and thiadiazole metal complexes.

Two complexes [KLa(HL(1))2{(CH3)2NCHO}2(H2O)3] (1) and [Sm(H2O)9](E-H2L(2))3·2H2O (2) were synthesized by the reaction of lanthanum(III) and samarium(III) nitrates with potassium 3-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2-hydroxy-5-nitrobenzenesulfonate (KH2L(1)) and potassium (E,Z)-5-chloro-3-(2-(1,3-dioxo-1-phenylbutan-2-ylidene)hydrazinyl)-2-hydroxybenzenesulfonate (KH2L(2)), respectively. Both complexes were fully characterized by elemental analysis, IR, (1)H and (13)C NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. Cooperative E,Z→E isomerization of KH2L(2), induced by resonance assisted hydrogen bonding and ionic interactions, occurs upon the interaction with Sm(III). Catalytic activities of KH2L(1,2) and their lanthanide derivatives were evaluated in the Henry reaction of nitroethane with a variety of aromatic and aliphatic aldehydes. Good yields (up to 91%) and diastereoselectivities (syn/anti 3 : 1) were observed in the reactions catalyzed by 1 in water.

In spite of its impressive record in medicinal chemistry, the role of barbituric acid H 3 BA (pyrimidine-2,4,6(1 H ,3 H ,5 H )-trione) in coordination, organometallic and supramolecular chemistries has not yet been analyzed and reviewed. However, H 3 BA can be readily functionalized and provides rich opportunities to create coordination bonds and non-covalent interactions. Thus, derivatives of H 3 BA (barbituric acids, BAs) are widely used for the preparation of a wide range of complexes with various metals of almost all groups of the periodic table. The review systematizes information on the synthesis, tautomerism, acid–base properties of BAs and their use for the construction of organometallic and coordination compounds, as well as coordination polymers and supramolecular assemblies. The role of different metal ions and the structure of BAs in directing the preparative pathways and tuning particular structural properties of the resulting compounds are discussed. Some valuable applications of BAs, in particular in the construction of molecular receptors, magnetic and nonlinear optic materials, bioactive compounds, drug cocrystal design, catalysis and photochemistry are also envisaged.

This review concerns metal-catalyzed reactions of oxidation of alcohols to the respective products, mainly ketones and aldehydes, mostly within the period of 2010–2014. Both conventional and unconventional systems, not only with usual reagents, but also with uncommon and prospective ones, are overviewed, with recently achieved developments.

Phthalonitrile, acetoxime and cobalt(II) nitrate hexahydrate are combined in acetone with formation of stable and easy to handle Co(II) complex [Co{C6H4C(NH2)NC(ONCMe2)2}2](NO3)2 (1). Interaction of 1 with excess alcohols ROH (also used as solvents) and 2 equiv of (NH4)2S leads, in one-step, to alkyl 2-carbamimidoylbenzoate nitrates [C6H4COOR{2-C(NH2)2}]NO3 [R=CH3, C2H5, C3H7, CH(CH3)2]. Similarly, N1,N3-dialkyl-1H-isoindole-1,3-diaminate nitrates [C6H4C(NR′)NC(NR′)]NO3 [R=C3H7, C4H9, C(CH3)3, CH2CH2OH, CH2CH2SC2H5) can be directly produced from 1 by its reaction with 4 equiv of amines and 2 equiv of (NH4)2S in alcoholic media.

Radical reactions are involved in a multitude of relevant processes and their importance is increasingly recognized in different fields ranging from biochemistry to materials science. For instance, radical polymerization accounts for approximately 45% of world polymer production [1]; on the other hand, the involvement of transient radical species in enzyme regulated processes in living organisms has stimulated, in recent years, enormous research efforts to rationalize their role in key physiological processes like mitochondrial respiration and aging [2, 3] or in the pathogenesis of several diseases [4]. Perhaps the best known example of radical reaction is hydrocarbon autoxidation, a chain process that affects any organic material, from food to petrol‐derived chemicals to human beings, existing under an oxygen‐rich atmosphere [5]. As a consequence, antioxidants and radical‐chain inhibitors are among the most important compounds used to control key radical reactions [5]. They act by trapping chain‐carrying radical species, thereby competing with chain propagation, as illustrated in Scheme 20.1. Their rational design and use need to be strictly based on their reactivity with radical species. Indeed, the understanding of radical reactions and their role in biology, along with their use and control in synthetic chemistry or in medicine, requires detailed knowledge of their kinetics and how it is influenced by the reaction medium. In this chapter it will be explained how non‐covalent interactions control the rates and the products of reactions that are typical of the radicals involved in autoxidation, namely, peroxyl (ROO∙), phenoxyl (PhO∙), and alkoxyl (RO∙) radicals. These radicals are not only of biological interest, but they are also key intermediates in green synthesis protocols, which aim at obtaining fine chemicals from renewable materials under mild conditions. For this reason, we will illustrate some selected examples of biomimetic radical reactions that are made possible by the control of these reactive intermediates by non‐covalent interactions