Reactivity of bulky tris(Phenylpyrazolyl) methanesulfonate copper(I) complexes towards small unsaturated molecules

Reaction of the tris(3-phenylpyrazolyl)methane sulfonate species (Tpms(Ph))Li with the copper(I) complex [Cu(MeCN)(4)][PF6] affords [Cu(Tpms(Ph))(MeCN)] 1. The latter, upon reaction with equimolar amounts of cyclohexyl-(CyNC) or 2,6-dimethylphenyl (XylNC) isocyanides, or excess CO, furnishes the corresponding Cu(I)complexes [Cu(Tpms(Ph))(CNR)] (R = Cy 2, Xyl 3) or [Cu(Tpms(Ph))(CO)] 4. The ligated isocyanide in 2 or 3 (or the acetonitrile ligand in 1)is displaced by 3-iminoisoindolin-1-one to afford 5, the first copper(I) complex containing an 3-iminoisoindolin-1-one ligand. The ligated acetonitrile in 1 undergoes nucleophilic attack by methylamine to give the amidine complex [Cu(Tpms(Ph)){MeC(NH)NHMe}] 6, whereas only the starting materials were recovered from the attempted corresponding reactions of 2 and 3 with methylamine. Complexes 1 or 6 form the trinuclear hydroxo-copper(II)species [(mu-Cu){Cu(mu-OH) (2)(Tpms(Ph))}(2)] 7 upon air oxidation in moist methanol. In all the complexes the scorpionate ligand facially caps the metal in the N,N,O-coordination mode

Cyclic carbonate synthesis from CO2and epoxides using zinc(II) complexes of arylhydrazones of β-diketones

Zinc(II) complexes of arylhydrazones of β-diketones (AHBD) were used for the first time as catalysts combined with tetrabutylammonium bromide (TBABr), in the coupling reaction between CO2 and epoxides. The influence of pressure and temperature on cyclic carbonate formation was investigated, as well as the catalytic activity toward different substrates (e.g. styrene oxide, propylene oxide and cyclohexene oxide). The molar ratio between metal complex and TBABr was determined for maximum catalytic activity

Metal-free and iron(II)-assisted oxidation of cyclohexane to adipic acid with ozone: A theoretical mechanistic study

Adipic acid has a tremendous applied importance. Its industrial synthesis requires harsh conditions and application/emission of hazardous HNO3 and N2O. Here, a mechanism of ecologically benign neat cyclohexane (CyH) oxidation with ozone into adipic acid under room temperature and radiation-free conditions, both metal-free and catalyzed by the iron(II) complex [FeCl2{κ3-HC(pz)3}] (pz = pyrazol-1-yl), was investigated by theoretical methods. Relatively high activation barriers of the rate limiting H-abstractions by O3 without a catalyst explain the experimentally observed low CyH conversion and selectivity toward adipic acid due to efficient accumulation of cyclohexanone. The active catalytic form [FeIV(=O)Cl2{κ3-HC(pz)3}] improves both CyH conversion and selectivity because it is a much more efficient H-abstractor compared to O3 and provides facile decomposition of CyH and cyclohexanone, opens up a new route to the formation of ortho-cyclohexanediol and then adipic acid, and prevents the accumulation of adipic anhydride – one of the stable intermediates under metal-free conditions. © 2021 Elsevier Inc

Recent Developments in Enantioselective Organocatalytic Cascade Reactions for the Construction of Halogenated Ring Systems

Chiral halogenated substances have many applications in pharmaceuticals, agrochemicals, and materials, such as polymers, liquid crystals and as intermediates in synthesis. The presence of a halogen atom in a molecule can have a large effect in its properties; for instance, halogens are used in drugs to improve lipophilicity, membrane permeability and absorption, and even the blood-brain barrier permeability. As highlighted in this review, there are nowadays a range of highly selective, versatile halogenating reagents, electrophilic, nucleophilic or radical in nature, which operate under mild conditions, allowing late-stage functionalization of complex molecules in cascade reactions. Recent developments in organocatalyst design revealed novel Cinchona alkaloids derivatives, chiral phosphoric acids, amines, phosphines and several bifunctional catalysts, mostly thiourea- or squaramide-based, which introduced chirality, with high levels of enantio- and diastereoselection, in the formation of one or multiple chiral centers in a single synthetic operation, as shown. In this review we survey the literature published in this field from 2014 to 2020. © 2021 Wiley-VCH Gmb

Novel H-bonded synthons in copper supramolecular frameworks with aminoethylpiperazine-based ligands. Synthesis, structure and catalytic activity

New Schiff base complexes [Cu2(HL1)(L1)(N3)3]·2H2O (1) and [Cu2L2(N3)2]·H2O (2) were synthesized. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analysis. The HL1 ligand results from the condensation of salicylaldehyde and 1-(2-aminoethyl)piperazine, while a new organic ligand, H2L2, was formed by the dimerization of HL1 via a coupling of two piperazine rings of HL1 on a carbon atom coming from DMF solvent. The dinuclear building units in 1 and 2 are linked into complex supramolecular networks through hydrogen and coordination bondings, resulting in 2D and 1D architectures, respectively. Single-point and broken-symmetry DFT calculations disclosed negligible singlet–triplet splittings within the dinuclear copper fragments in 1 and 2. Catalytic studies showed a remarkable activity of 1 and 2 towards cyclohexane oxidation with H2O2 in the presence of nitric acid and pyridine as promoters and under mild conditions (yield of products up to 21%). Coordination compound 1 also acts as an active catalyst in the intermolecular coupling of cyclohexane with benzamide using di-tert-butyl peroxide (tBuOOtBu) as a terminal oxidant. Conversion of benzamide at 55% was observed after 24 h reaction time. By-product patterns and plausible reaction mechanisms are discussed. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Urea and thiourea based coordination polymers and metal-organic frameworks: Synthesis, structure and applications

Coordination polymers (CPs) and metal–organic frameworks (MOFs) are commonly constructed by self-assembly of metal ions and multidentate organic linkers and have gained a significant attention in the past two decades. Due to their structural properties, high chemical and thermal stability and tunable pore sizes, they show potential application in different areas, such as gas adsorption and separation, catalysis, sensing, drug delivery, etc. Moreover, their tunability with functional organic ligands is of unquestionably importance due to the limitless possibility of designing various functional organic linkers as well as the particular chemical properties of functional groups. Designing of CPs/MOFs by incorporating different functionalities can be undertaken either via direct synthesis or via modification of ligand or metal centre. Due to the conformational flexibility, strong hydrogen bonding capabilities and polarizability of the urea and thiourea groups, recently a significant attention has been dedicated to developing functionalized CPs/MOFs with such moieties. These functional groups decorated compounds can show not only attractive structures but also a significant improvement in gas adsorption, catalytic and sensing properties. Although this area of research has been developed remarkably in the last few years, it had not yet been reviewed. This review describes recent developments in urea and thiourea functionalized frameworks by discussing their synthesis, structure and applications. It addresses the different synthetic methodologies, followed by their structural description. Lastly, their applications on gas adsorptions and separation, heterogeneous catalytic reactions, and sensing are described. The effects of functional groups on the structure and applications of functionalized materials are also discussed. © 2021 Elsevier B.V

Water oxidation with transition metal catalysts with non-innocent ligands and its mechanisms

Transition metal complexes acting as catalysts towards water oxidation concern a challenging research topic with high relevance in solar and fuel conversion technologies. Non-innocent ligands with redox behavior can contribute with an important role on this field. We review herein the use as catalysts of complexes (containing single or double metal sites) with such a type of ligands on water oxidation and the corresponding reaction mechanisms as established by kinetic, electrochemical and theoretical studies. © 2021 Elsevier B.V

A new amido-phosphane as ligand for copper and silver complexes. Synthesis, characterization and catalytic application for azide-alkyne cycloaddition in glycerol

The new sterically hindered amido-phosphane 1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane-3,7-diylbis(phenylmethanone), DBPTA (1), has been obtained via an open-cage double N-acylation of 1,3,5-triaza-7-phosphadamantane (PTA) using benzoic anhydride. DBPTA is the only acyl derivative of PTA that contains an aromatic appendage. Due to the bulky nature of the benzoyl C(O)Ph groups, they exhibit mutual anti configuration as confirmed by solution NMR and single crystal X-ray diffraction. Compound 1 is readily soluble in common polar organic and green solvents, making it a very versatile ligand that could be used in a variety of reaction systems. To assess the coordination characteristics of the new phosphane, seven copper complexes of formulas [Cu(DBPTA)4]BF4 (2), [CuX(DBPTA)3] {X = Br (3) and I (4)}, [Cu(μ-X)(DBPTA)2]2 {X = Br (5) and I (6)}, [Cu(bpy)(DBPTA)2]Y {Y = BF4 (7) and BPh4 (8)} {bpy = 2,2′-bipyridine}, and three silver complexes with formulas [Ag(DBPTA)4]NO3 (9), [Ag(Tpm∗)(DBPTA)]NO3 (10) and [Ag(Tpms)(DBPTA)] (11) {Tpm∗ = tris(3,5-dimethyl-1-pyrazolyl)methane, Tpms = tris(pyrazol-1-yl)methanesulfonate} have been synthesised. Compounds 1-11 were characterized by elemental analyses and electrospray ionization mass spectrometry (ESI-MS), as well as by FT-IR and NMR (1H, 13C, 31P, COSY and HSQC) spectroscopic techniques. The catalytic activity of the complexes has been investigated for 1,3-dipolar azide-alkyne cycloaddition reaction using glycerol as a reaction medium to afford 1,4-disubstituted-1,2,3-triazoles. Complex 7 was found to be the most efficient catalyst, affording triazoles in yields up to 97% after 18 h under standard bench experimental conditions (at 23 °C, aerobic conditions and in the absence of any additional bases) and up to 98% after 15 minutes under microwave irradiation (125 °C, 30 W). The catalysis proceeds with a broad substrate scope according to "Click"rules providing a significant contribution to "Green Chemistry". © 2021 The Royal Society of Chemistry

Phenoxazinone synthase-like catalytic activity of novel mono- And tetranuclear copper(ii) complexes with 2-benzylaminoethanol

Three novel coordination compounds, [Cu(ca)2(Hbae)2] (1), [Cu(va)2(Hbae)2] (2) and [Cu4(va)4(bae)4]·H2O (3), have been prepared by self-assembly reactions of copper(ii) chloride (1 and 2) or tetrafluoroborate (3) and CH3OH (1 and 3) or CH3CN (2) solution of 2-benzylaminoethanol (Hbae) and cinnamic (Hca, 1) or valeric (Hva, 2 and 3) acid. Crystallographic analysis revealed that both 1 and 2 have mononuclear crystal structures, wherein the complex molecules are H-bonded forming extended supramolecular chains. The tetranuclear structure of 3 is based on the {Cu4(μ3-O)4} core, wherein the metal atoms are bound together by μ3 oxygen bridges from 2-benzylaminoethanol forming an overall cubane-like configuration. The strong hydrogen bonding in 1-3 leads to the joining of the neighbouring molecules into 1D chains. Concentration-dependent ESI-MS studies disclosed the equilibria between di-, tri- and tetranuclear species in solutions of 1-3. All three compounds act as catalysts for the aerobic oxidation of o-aminophenol to the phenoxazinone chromophore (phenoxazinone synthase-like activity), with the maximum reaction rates of 4.0 × 10-7, 2.5 × 10-7 and 2.1 × 10-7 M s-1 for 1, 2 and 3, respectively, supported by the quantitative yield of the product after 24 h. The dependence of the reaction rates on catalyst concentrations is evidence of reaction orders higher than one relative to the catalyst. Kinetic and ESI-MS data allowed us to assume that the tetranuclear species, originating from 1, 2 and 3 in solution, possess considerably higher activity than the species of lower nuclearity. Mechanistic and isotopic 18O-labelling experiments suggested that o-aminophenol coordinates to CuII species with the formation of reactive intermediates, while the oxygen from 18O2 is not incorporated into the phenoxazinone chromophore. © 2020 The Royal Society of Chemistry