C-Heterogenized Re Nanoparticles as Effective Catalysts for the Reduction of 4-Nitrophenol and Oxidation of 1-Phenylethanol

Rhenium nanoparticles (Re NPs) supported on Norit (activated carbon—C) and graphene (G) were prepared by a solvothermal method under microwave irradiation (MW). The synthesised heterogeneous catalysts were characterised and tested as reduction and oxidation catalysts, highlighting their dual catalytic behaviour. In the first case, they were used, for the first time, to reduce 4-nitrophenol, in aqueous medium, under MW irradiation. Re catalysts were easily recovered by centrifugation and recycled up to six times without significant activity loss. However, the same Re catalysts in MW-assisted oxidation of 1-phenylethanol with no added solvent experienced a significant loss of activity when recycled. The higher activity of the rhenium nanoparticles supported on graphene (Re/G) catalyst in both reactions was assigned to the higher dispersion and smaller particle size of Re NPs when graphene is the support.

Tetracopper(II) Cores Driven by an Unexplored Trifunctional Aminoalcohol Sulfonic Acid for Mild Catalytic C–H Functionalization of Alkanes

Three new tetracopper(II) coordination compounds were easily generated from Cu(NO3)2, a trifunctional aminoalcohol sulfonic acid (H3bes, N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid) as a principal building block, and a benzene carboxylic acid as a supporting ligand (i.e., benzoic (Hba), 4-hydroxybenzoic (Hfba), or 3-hydroxybenzoic (Hthba) acid). The obtained microcrystalline products, [Cu4(µ-Hbes)3(µ-H2bes)(µ-L)]·2H2O (L = ba− (1), fhba− (2), and thba− (3)), were fully characterized by FTIR (Fourier-transform infrared spectroscopy), elemental analysis, ESI-MS (Electrospray Ionisation Mass Spectrometry), and single-crystal X-ray diffraction methods. Compounds 1–3 were applied as effective homogeneous catalysts in the oxidative C−H functionalization of alkanes (cycloalkanes and propane). Two different model reactions were explored: (1) mild oxidation of alkanes with hydrogen peroxide to give alcohols and ketones, and (2) mild carboxylation of alkanes with carbon monoxide, water, and potassium peroxodisulfate to give carboxylic acids. For these reactions, effects of different parameters, as well as mechanistic and selectivity characteristics, were studied.

Extending the family of quinolone antibacterials to new copper derivatives: self-assembly, structural and topological features, catalytic and biological activity

New copper(ii) compounds with quinolone pefloxacin were synthesized and fully characterized; they exhibit notable catalytic activity and promising biological profiles.

Mixed-ligand aminoalcohol-dicarboxylate copper(II) coordination polymers as catalysts for the oxidative functionalization of cyclic alkanes and alkenes

New copper(II) catalytic systems for the mild oxidative C–H functionalization of cycloalkanes and cycloalkenes were developed, which are based on a series of mixed-ligand aminoalcohol-dicarboxylate coordination polymers, namely [Cu2(μ-dmea)2(μ-nda)(H2O)2]n·2nH2O (1), [Cu2(μ-Hmdea)2(μ-nda)]n·2nH2O (2), and [Cu2(μ-Hbdea)2(μ-nda)]n·2nH2O (3) that bear slightly different dicopper(II) aminoalcoholate cores, as well as on a structurally distinct dicopper(II) [Cu2(H4etda)2(μ-nda)]·nda·4H2O (4) derivative [abbreviations: H2nda, 2,6-naphthalenedicarboxylic acid; Hdmea, N,N′-dimethylethanolamine; H2mdea, N-methyldiethanolamine; H2bdea, N-butyldiethanolamine; H4etda, N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine]. Compounds 1–4 act as homogeneous catalysts in the three types of model catalytic reactions that proceed in aqueous acetonitrile medium under mild conditions (50–60°C): (i) the oxidation of cyclohexane by hydrogen peroxide to cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone, (ii) the oxidation of cycloalkenes (cyclohexene, cyclooctene) by hydrogen peroxide to a mixture of different oxidation products, and (iii) the single-pot hydrocarboxylation of cycloalkanes (cyclopentane, cyclohexane, cycloheptane, cyclooctane) by carbon monoxide, water, and a peroxodisulfate oxidant into the corresponding cycloalkanecarboxylic acids. The catalyst and substrate scope as well as some mechanistic features were investigated; the highest catalytic activity of 1–4 was observed in the hydrocarboxylation of cycloalkanes, allowing to achieve up to 50% total product yields (based on substrate).

Self-assembly generation, structural features, and oxidation catalytic properties of new aqua-soluble copper(ii)-aminoalcohol derivatives

Multidentate aminoalcohols were applied as unexplored building blocks to generate two novel Cu(ii) coordination compounds that act as efficient catalysts for the mild and acid-promoter-free oxidation of C₅–C₈ cycloalkanes.

Aminoalcohols and benzoates-friends or foes? Tuning nuclearity of Cu(ii) complexes, studies of their structures, magnetism, and catecholase-like activities as well as performing DFT and TDDFT studies

The Cu(ii) complexes of varying nuclearity are synthesized, characterized and assessed for catecholase activities.

New aqua-soluble dicopper(ii) aminoalcoholate cores for mild and water-assisted catalytic oxidation of alkanes

Two new dicopper(ii) pre-catalysts were synthesized, fully characterized, and applied for the mild homogeneous oxidation of alkanes.

Cobalt complexes with pyrazole ligands as catalyst precursors for the peroxidative oxidation of cyclohexane: X-ray absorption spectroscopy studies and biological applications

[CoCl(μ-Cl)(Hpz(Ph))3]2 (1) and [CoCl2(Hpz(Ph))4] (2) were obtained by reaction of CoCl2 with HC(pz(Ph))3 and Hpz(Ph), respectively (Hpz(Ph)=3-phenylpyrazole). The compounds were isolated as air-stable solids and fully characterized by IR and far-IR spectroscopy, MS(ESI+/-), elemental analysis, cyclic voltammetry (CV), controlled potential electrolysis, and single-crystal X-ray diffraction. Electrochemical studies showed that 1 and 2 undergo single-electron irreversible Co(II)→Co(III) oxidations and Co(II)→Co(I) reductions at potentials measured by CV, which also allowed, in the case of dinuclear complex 1, the detection of electronic communication between the Co centers through the chloride bridging ligands. The electrochemical behavior of models of 1 and 2 were also investigated by density functional theory (DFT) methods, which indicated that the vertical oxidation of 1 and 2 (that before structural relaxation) affects mostly the chloride and pyrazolyl ligands, whereas adiabatic oxidation (that after the geometry relaxation) and reduction are mostly metal centered. Compounds 1 and 2 and, for comparative purposes, other related scorpionate and pyrazole cobalt complexes, exhibit catalytic activity for the peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone under mild conditions (room temperature, aqueous H2O2). In situ X-ray absorption spectroscopy studies indicated that the species derived from complexes 1 and 2 during the oxidation of cyclohexane (i.e., Ox-1 and Ox-2, respectively) are analogous and contain a Co(III) site. Complex 2 showed low in vitro cytotoxicity toward the HCT116 colorectal carcinoma and MCF7 breast adenocarcinoma cell lines.

New p-tolylimido rhenium(v) complexes with carboxylate-based ligands: synthesis, structures and their catalytic potential in oxidations with peroxides

Novel p-tolylimido rhenium(v) complexes were obtained and calculations at the DFT level were undertaken. The complexes exhibited high catalytic activity in oxidation of alkanes and alcohols with H₂O₂ or TBHP.

Oxorhenium complexes bearing the water-soluble tris(pyrazol-1-yl)methanesulfonate, 1,3,5-triaza-7-phosphaadamantane, or related ligands, as catalysts for Baeyer-Villiger oxidation of ketones

New rhenium(VII or III) complexes [ReO3(PTA)2][ReO4] (1) (PTA = 1,3,5-triaza-7-phosphaadamantane), [ReO3(mPTA)][ReO4]I (2) (mPTA = N-methyl-1,3,5-triaza-7-phosphaadamantane cation), [ReO3(HMT)2][ReO4] (3) (HMT = hexamethylenetetramine), [ReO3(η(2)-Tpm)(PTA)][ReO4] (4) [Tpm = hydrotris(pyrazol-1-yl)methane, HC(pz)3, pz = pyrazolyl], [ReO3(Hpz)(HMT)][ReO4] (5) (Hpz = pyrazole), [ReO(Tpms)(HMT)] (6) [Tpms = tris(pyrazol-1-yl)methanesulfonate, O3SC(pz)3(-)] and [ReCl2{N2C(O)Ph}(PTA)3] (7) have been prepared from the Re(VII) oxide Re2O7 (1-6) or, in the case of 7, by ligand exchange from the benzoyldiazenido complex [ReCl2{N2C(O)Ph}(Hpz)(PPh3)2], and characterized by IR and NMR spectroscopies, elemental analysis and electrochemical properties. Theoretical calculations at the density functional theory (DFT) level of theory indicated that the coordination of PTA to both Re(III) and Re(VII) centers by the P atom is preferable compared to the coordination by the N atom. This is interpreted in terms of the Re-PTA bond energy and hard-soft acid-base theory. The oxo-rhenium complexes 1-6 act as selective catalysts for the Baeyer-Villiger oxidation of cyclic and linear ketones (e.g., 2-methylcyclohexanone, 2-methylcyclopentanone, cyclohexanone, cyclopentanone, cyclobutanone, and 3,3-dimethyl-2-butanone or pinacolone) to the corresponding lactones or esters, in the presence of aqueous H2O2. The effects of a variety of factors are studied toward the optimization of the process.

Mild, single-pot hydrocarboxylation of gaseous alkanes to carboxylic acids in metal-free and copper-promoted aqueous systems

A direct, selective and highly efficient method has been developed for the hydrocarboxylation of C(n) gaseous alkanes into C(n+1) carboxylic acids, in aqueous acid-solvent-free medium at low temperatures. The approach is based on a metal-free or copper-promoted reaction of ethane, propane or n-butane with carbon monoxide and water, in a H(2)O/MeCN medium at 50-60 degrees C, in the presence of potassium peroxodisulfate. The effects of various reaction parameters, such as the absence or presence of a copper promoter, solvent composition, temperature, time, CO and alkane pressure, were studied. A free radical mechanism was confirmed by radical trap experiments involving acyl radical formation, oxidation and subsequent hydroxylation by water. Remarkable yields (based on alkane) of carboxylic acids in the 34-41 % range were achieved even in the metal-free systems, although in the presence of a tetracopper(II) triethanolaminate derived promoter they reach superior values of 58 and 87 % for the hydrocarboxylations of propane and n-butane, respectively; in these cases, branched isobutyric and 2-methylbutyric acids were the predominant products. From a green perspective, important features of the present alkane hydrocarboxylations include the exceptional metal-free, mild and acid-solvent-free reaction conditions, the operation in aqueous medium with a rare hydroxylating role of water, with high selectivities, and yields of carboxylic acids. Taken together, these conditions correspond to the mildest and the most efficient method so far reported for the oxidative functionalisation of gaseous alkanes.

Synthesis, X-Ray Structure, and Characterization of Catena-bis(benzoate)bis{N,N-bis(2-hydroxyethyl)glycinate}cadmium(II)

The reaction of N, N-bis(2-hydroxyethyl)glycine (bicine; bicH₃) with Cd(O₂CPh)₂ · 2H₂O in MeOH yielded the polymeric compound [Cd₂(O₂CPh)₂(bicH₂)₂]_n(1). The complex crystallizes in the tetragonal space group P4₁2₁2. The lattice constants are a = b = 12.737(5) and c = 18.288(7) Å. The compound contains chains of repeating {Cd₂(O₂CPh)₂(bicH₂)₂} units. One Cd^II atom is coordinated by two carboxylate oxygen, four hydroxyl oxygen, and two nitrogen atoms from two symmetry-related 2.21111 (Harris notation) bicH₂⁻ ligands. The other Cd^II atom is coordinated by six carboxylate oxygen atoms, four from two bicH₂⁻ ligands and two from the monodentate benzoate groups. Each bicinate(-1) ligand chelates the 8-coordinate, square antiprismatic Cd^II atom through one carboxylate oxygen, the nitrogen, and both hydroxyl oxygen atoms and bridges the second, six-coordinate trigonal prismatic Cd^II center through its carboxylate oxygen atoms. Compound 1 is the first structurally characterized cadmium(II) complex containing any anionic form of bicine as ligand. IR data of 1 are discussed in terms of the coordination modes of the ligands and the known structure.

Rhenium complexes of tris(pyrazolyl)methanes and sulfonate derivative

The trioxo [ReO(3){SO(3)C(pz)(3)}] (1) (pz = pyrazolyl) and oxo [ReOCl{SO(3)C(pz)(3)}(PPh(3))]Cl (2) compounds with tris(pyrazolyl)methanesulfonate were obtained by treatment of Re(2)O(7) or [ReOCl(3)(PPh(3))(2)], respectively, with Li[SO(3)C(pz)(3)], whereas [ReCl(3){HC(pz)(3)}] (3), [ReCl(3){HC(3,5-Me(2)pz)(3)}] (4) and [ReCl(4){eta(2)-HC(pz)(3)}] (5) were prepared by reaction of [ReOCl(3)(PPh(3))(2)] (3,4) or [ReCl(4)(NCMe)(2)] (5) with hydrotris(pyrazolyl)methane HC(pz)(3) (3,5) or hydrotris(3,5-dimethyl-1-pyrazolyl)methane HC(3,5-Me(2)pz)(3) (4). [ReO{SO(3)C(pz)(3)}{OC(CH(3))(2)pz}][ReO(4)] 6, with a chelated pyrazolyl-alkoxide, was derived from an unprecedented ketone-pyrazolyl coupling on reaction of crude 1 with acetone. The compounds have been characterized by elemental analyses, IR and NMR spectroscopies, FAB-MS spectrometry and cyclic voltammetry and, in the case of 5 and 6, also by single-crystal X-ray diffraction. The electrochemical E(L) Lever parameter has been estimated, for the first time, for the SO(3)C(pz)(3)(-) and oxo ligands allowing the measurement of their electron-donor character and comparison with other ligands. Compounds 1, 2 and 6 appear to be the first tris(pyrazolyl)methanesulfonate complexes of rhenium to be reported.