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The transformation of biomass, a carbon resource presenting a huge potential to produce valuable chemicals, requires the search for sustainable catalytic routes. This work proposes the microwave-assisted oxidation of biomass -derived substrates, such as glycerol and the furfural derivatives 5-(hydroxymethyl)furfural (HMF) and 5-hydroxymethyl-2-furancarboxylic acid (HFCA), using the C-scorpionate dichloro-gold(III) complex [AuCl2(κ2-Tpm)]Cl (Tpm = HCpz3; pz = pyrazol-1-yl) as a catalyst, as prepared and supported on graphene, in solvent-free conditions. The unprecedented application of a mechanochemical procedure (in a planetary ball mill, in solid state) to synthesize a C-scorpionate complex, the [AuCl2(κ2-Tpm)]Cl, is disclosed. The immobilization of [AuCl2(κ2-Tpm)]Cl on graphene was performed using different methods, including some (e.g., microwave irradiation and liquid assisted grinding) for the first time. The structural properties and the performance of the prepared catalytic materials are presented and discussed.

Pd(II) and Pt(II) composites with activated carbon (AC), graphene oxide, and multiwalled carbon nanotubes were prepared by ball milling and used as catalysts for the Suzuki-Miyaura reaction, under several energy inputs (mechanical grinding, conventional heating, and microwave irradiation). The catalytic composites were characterized by ICP-MS, BET, XPS analyses, TEM, and SEM. The average particle size of the prepared composites was estimated to be in the range of 6–30 nm, while the loadings of Pd and Pt did not significantly affect the surface area of the AC support due to the tendency to agglomerate as observed by the TEM analysis. The Pd/AC composites exhibit high mechanochemical catalytic activity in cross-coupling of bromobenzene and phenylboronic acid with molar yields up to 80% with TON and TOF of 222 and 444 h−1, respectively, achieved with Pd(4.7 wt%)-AC catalyst under the liquid assisted grinding for 0.5 h at ambient conditions, using cyclohexene as an additive.

Iron-containing particulate catalysts of 0.1−1 µm 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.

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−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−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−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.

The structure of the title compound, [Cu(PTA)4]Cl·6H2O (PTA is 1,3,5-triaza-7-phosphaadamantane, C6H12N3P), is composed of discrete monomeric [Cu(PTA)4]+ cations, chloride anions and uncoordinated water molecules. The CuI atom exhibits tetrahedral coordination geometry, involving four symmetry-equivalent P–bound PTA ligands. The structure is extended to a regular three-dimensional supramolecular framework via numerous equivalent O—H...N hydrogen bonds between all solvent water molecules (six per cation) and all PTA N atoms, thus simultaneously bridging each [Cu(PTA)4]+ cation with 12 neighbouring units in multiple directions. The study also shows that PTA can be a convenient ligand in crystal engineering for the construction of supramolecular architectures.

A novel parato metashift of a nitro group at the phenyl ring of 3-(2-hydroxy-4-nitrophenylhydrazo)pentane-2,4-dione (H2L1, 1), with formation of the new 3-(2-hydroxy-3,5-dinitrophenylhydrazo)pentane-2,4-dione (H2L2, 2), occurs upon nitration of 1with an equimolar amount of NaNO2, under basic conditions. 2acts as a polydentate ligand for the synthesis of the polymeric potassium [K(μ5-HL2)]n(3) and monomeric nickel(ii) [Ni(H2O)3(L2)]·H2O (4) compounds. They have been fully characterized, including single crystal X-ray analysis, and the complexes feature metal–organic (in 3) or supramolecular (in 4) 3D networks. The topological analysis of 3reveals a uninodal 5-connected underlying net with the point symbol of (46.64) and a very rare 5/4/t5 topology, which had not yet been observed in coordination polymers. [ABSTRACT FROM AUTHOR]

New 3D Cu(II)-K coordination polymers (CPs), [CuK(μ7-L1)(H2O)]n·nH2O (1), and [CuK(μ5-L2)(H2O)]n·2nH2O (2), were easily generated by self-assembly from copper(II) nitrate, potassium hydroxide, and azo derivatives of β-diketones, namely 3-(2-hydroxy-3-sulfo-5-chlorophenylhydrazo)pentane-2,4-dione (H3L1) or 3-(2-hydroxy-3-sulfo-5-nitrophenylhydrazo)pentane-2,4-dione (H3L2). The single-crystal structures of 1and 2disclose similar 3D metal–organic networks, driven by the 5-connected potassium, 6-connected L1, or 5-connected L2nodes. The topological analysis of 1reveals a rare binodal 5,6-connected underlying net with an unprecedented topology defined by the point (Schläfli) symbol of (3·45·53·6)(32·46·53·64), while 2features a uninodal 5-connected net with the bnn(hexagonal boron nitride) topology and the point symbol of (46·64). Both networks possess voids filled by crystallization water molecules, the reversible escape and binding of which was studied by thermal analyses. Upon a dehydration–adsorption cycle, 1undergoes structural changes, although without loss of crystallinity, while 2basically preserves its initial structure, as confirmed by X-ray powder diffraction analyses. Besides, 1and 2act as catalyst precursors for the aerobic TEMPO-mediated selective oxidation of benzyl alcohol to benzaldehyde in aqueous medium. [ABSTRACT FROM AUTHOR]

The zinc(ii) complexes with ortho-hydroxy substituted arylhydrazo-β-diketonates [Zn2(CH3OH)2(μ-L1)2] (5), [Zn{(CH3)2SO}(H2O)(L2)] (6), [Zn2(H2O)2(μ-L3)2] (7) and [Zn(H2O)2(L4)]·H2O (8) were synthesized by reaction of a zinc(ii) salt with the appropriate hydrazo-β-diketone, HO-2-C6H4-NHNC{C(O)CH3}2(H2L1, 1), HO-2-O2N-4-C6H3-NHNC{C(O)CH3}2(H2L2, 2), HO-2-C6H4-NHNCC(O)CH2C(CH3)2CH2C(O) (H2L3, 3) or HO-2-O2N-4-C6H3-NHNCC(O)CH2C(CH3)2CH2C(O) (H2L4, 4). They were fully characterized, namely by X-ray diffraction analysis that disclosed the formation of extensive H-bonds leading to 1D chains (5and 6), 2D layers (7) or 3D networks (8). The thermodynamic parameters of the Zn(ii) reaction with H2L2in solution, as well as of the thermal decomposition of 1–8were determined. Complexes 5–8act as diastereoselective catalysts for the nitroaldol (Henry) reaction. The threo/erythrodiastereoselectivity of the β-nitroalkanol products ranges from 8 : 1 to 1 : 10 with typical yields of 80–99%, depending on the catalyst and substrate used. [ABSTRACT FROM AUTHOR]

Reactions of copper(ii) with 3-phenylhydrazopentane-2,4-diones X-2-C6H4–NHNC{C(O)CH3}2bearing a substituent in the ortho-position [X = OH (H2L1) 1, AsO3H2(H3L2) 2, Cl (HL3) 3, SO3H (H2L4) 4, COOCH3(HL5) 5, COOH (H2L6) 6, NO2(HL7) 7or H (HL8) 8] lead to a variety of complexes including the monomeric [CuL4(H2O)2]·H2O 10, [CuL4(H2O)2] 11and [Cu(HL4)2(H2O)4] 12, the dimeric [Cu2(H2O)2(μ-HL2)2] 9and the polymeric [Cu(μ-L6)]n] 13ones, often bearing two fused six-membered metallacycles. Complexes 10–12can interconvert, depending on pH and temperature, whereas the Cu(ii) reactions with 4in the presence of cyanoguanidine or imidazole (im) afford the monomeric compound [Cu(H2O)4{NCNC(NH2)2}2](HL4)2·6H2O 14and the heteroligand polymer [Cu(μ-L4)(im)]n15, respectively. The compounds were characterized by single crystal X-ray diffraction (complexes), electrochemical and thermogravimetric studies, as well as elemental analysis, IR, 1H and 13C NMR spectroscopies (diones) and ESI-MS. The effects of the substituents in 1–8on the HOMO–LUMO gap and the relative stability of the model compounds [Cu(OH)(L8)(H2O)]·H2O, [Cu(L1)(H2O)2]·H2O and [Cu(L4)(H2O)2]·H2O are discussed on the basis of DFT calculations that show the stabilization follows the order: two fused 6-membered > two fused 6-membered/5-membered > one 6-membered metallacycles. Complexes 9, 10, 12and 13act as catalyst precursors for the peroxidative oxidation (with H2O2) of cyclohexane to cyclohexanol and cyclohexanone, in MeCN/H2O (total yields of ca. 20% with TONs up to 566), under mild conditions. [ABSTRACT FROM AUTHOR]

[2 + 3] cycloaddition of the pyrrolin N-oxide −O+NCHCH2CH2CMe22with 2-cyanopyridine NC5H4(2-CN) 1ain the presence of PdCl2at room temperature in acetone gives the ketoimine palladium(II) complex cis-[PdCl2{N(=CCH2CH2C(Me)2NH)C(=O)C5H4N}] 3acontaining the (E)-N-(5,5-dimethylpyrrolidin-2-ylidene)picolinamide ligand, in good yield (85%). The reaction of 2with 3-cyanopyridine NC5H4(3-CN) 1bor 4-cyanopyridine NC5H4(4-CN) 1cunder the same experimental conditions gives the simple adducts of cyanopyridines trans-[PdCl2{NC5H4(3-CN)}2] 4bor trans-[PdCl2{NC5H4(4-CN)}2] 4c, respectively. When the cyanopyridines NC5H3R1R21(R1= 2-CN, R2= H 1a; R1= 3-CN, R2= H 1b; R1= 4-CN, R2= H 1c; R1= 4-CN, R2= 2-Cl 1d; R1= 3-CN, R2= 5-Me 1e) are heated at 100 °C for 12 h with 2-butanone oxime (used as a reagent and solvent) in the presence of PdCl2, the 2,4-dipyridyl-1,3,5-triazapentadienate (or bis-imidoylamidinate) palladium(II) complexes [Pd{HNC(NC5H3R2)NC(NC5H3R2)NH}2] 5(2-NC5H3, R2= H 5a; 3-NC5H3, R2= H 5b; 4-NC5H3, R2= H 5c; 4-NC5H3, R2= 2-Cl 5d; 3-NC5H3, R2= 5-Me 5e) are synthesized by one-pot template transformations followed by deprotonation by a base (n-PrNH2). The compounds were characterized by IR, 1H and 13C NMR spectroscopies, FAB+-MS, elemental analyses and, in the cases of 3a, 5a, 5band 5d, also by X-ray diffraction analyses. The catalytic activity of complexes 3and 5was studied under microwave irradiation for C–C coupling reactions, in the solid phase on a silica gel support, and it was found that complex 3ais the most active one with the maximum TON of 2.0·105and TOF of 1.3·104min−1for Suzuki–Miyaura, and TON of 800 and TOF of 27 min−1for Heck reactions. [ABSTRACT FROM AUTHOR]

[2 + 3] Cycloaddition reactions of the organonitriles RCN 1(R = Me (1a), Et (1b), p-IC6H4(1c), p-BrC6H4(1d), p-ClC6H4(1e), p-FC6H4(1f)) with the pyrroline N-oxide −O+NCHCH2CH2CMe22in the presence of PdCl2proceed at room temperature for 12 h and allow the isolation of the corresponding palladium(ii) complexes trans-[PdCl2{NC(R)ONC(H)CH2CH2CMe2}2] 3a–3fcontaining fused bicyclic Δ4-1,2,4-oxadiazoline ligands, in good to excellent yields (75–90%). Treatment of trans-[PdCl2(EtCN)2] with the nitrone 2in acetone or propionitrile at room temperature affords, in good yield, 3b(R = Et), confirming that complexes 3are formed vianitrile activation by coordination. These reactions proceed with high diastereoselectivity and afford mixtures of enantiomers, due to the rigid conformation (E) of the cyclic nitrone 2. The oxadiazolines NC(R)ONC(H)CH2CH2CMe2(R = Et (4b), p-FC6H4(4f)) are liberated upon reaction of complexes 3b,3fwith a diphosphine (dppe). During the liberation of 4f, the complex trans-[PdCl2{NC(NHCOC6H4F-4)CH2CH2CMe2}2] 5was formed in a minor amount upon N–O bond cleavage of the oxadiazoline ring to give a pyrrolylbenzamide species coordinated by the N-atom of the pyrrolyl moiety. The compounds were characterized by IR, 1H and 13C NMR spectroscopies, ESI-MS, elemental analyses and, in the cases of 3b, 3dand 5, also by X-ray diffraction analyses. Complexes 3band 3fshow a high catalytic activity towards the microwave-assisted Suzuki–Miyaura cross-coupling reaction in aqueous medium, achieving a TON value of 2.7 × 105and a TOF value of 1.1 × 106h−1. [ABSTRACT FROM AUTHOR]

The copper(ii)-mediated integration between various 3-iminoisoindolin-1-ones and neat organonitriles (which play a dual role of solvent and reactant), under heating for ca. 12 h, and without requiring any base, accomplishes the release of the solid (1,3,5-triazapentadienato)CuII complexes [Cu{HN=C(R)NC(C6R1R2R3R4CO)N}2] (1–11) bearing the incorporated iminoisoindolin-1-one fragment. These compounds were isolated in moderate to good yields (44–78%) and do not require further purification. The iminoisoindolinone–nitrile coupling is CuII-mediated and has a general character insofar as it can be efficiently applied for both unsubstituted (R1–R4 = H) and substituted iminoisoindolin-1-ones (R1, R3, R4 = H, R2 = Me; R1, R4 = H, R2, R3 = Cl; R1–R4 = F), and a wide range of nitriles (R = Me, Et, Prn, Pri, C6H11, CH2Ph). Complexes 1–11 were characterized by elemental analyses (C, H, N), FAB+-MS, IR spectroscopy, and additionally compounds 1, 2 and 4 by single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]