Electronic and ring size effects of N-heterocyclic carbenes on the kinetics of ligand substitution reactions and DNA/protein interactions of their palladium(II) complexes

The synthesis, substitution kinetics and DNA/BSA interactions of four cationic Pd(II) complexes [Pd(1)Cl]BF4 (Pd1), [Pd(2)Cl]BF4 (Pd2), [Pd(3)Cl]BF4 (Pd3) and [Pd(4)Cl]BF4 (Pd4), derived from the reaction of [PdCl2(NCCH3)2] with ligands 2,6-bis(3-methylimidazolium-1-yl)pyridine dibromide (1), 2,6-bis(3-ethylimidazolium-1-yl)pyridine dibromide (2), 2,6-bis(1-methylimidazole-2-thione)pyridine (3), and 2,6-bis(1-ethylimidazole-2-thione)pyridine (4), respectively are reported. The complexes were characterised by various spectroscopic techniques and single crystal X-ray diffraction for compound Pd2. Kinetic reactivity of the complexes with the biologically relevant nucleophiles thiourea (Tu), L-methionine (L-Met) and guanosine 5'-monophosphate sodium salt (5'-GMP) was in the order: Pd1 > Pd2 > Pd3 > Pd4, which was largely dependent on the electronic and ring size of the chelate ligands, consistent with Density functional theory (DFT) simulations. The interactions of the complexes with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) binding titrations showed strong binding. Both the experimental and in silico data reveal CT-DNA intercalative binding mode.

A Reusable FeCl3∙6H2O/Cationic 2,2′-Bipyridyl Catalytic System for Reduction of Nitroarenes in Water

The association of a commercially-available iron (III) chloride hexahydrate (FeCl3∙6H2O) with cationic 2,2′-bipyridyl in water was proven to be an operationally simple and reusable catalytic system for the highly-selective reduction of nitroarenes to anilines. This procedure was conducted under air using 1–2 mol% of catalyst in the presence of nitroarenes and 4 equiv of hydrazine monohydrate (H2NNH2∙H2O) in neat water at 100 °C for 12 h, and provided high to excellent yields of aniline derivatives. After separation of the aqueous catalytic system from the organic product, the residual aqueous solution could be applied for subsequent reuse, without any catalyst retreatment or regeneration, for several runs with only a slight decrease in activity, proving this process eco-friendly.

Synthesis, Structure, and Catalytic Hydrogenation Activity of [NO]-Chelate Half-Sandwich Iridium Complexes with Schiff Base Ligands

A series of N,O-coordinate iridium(III) complexes with a half-sandwich motif bearing Schiff base ligands for catalytic hydrogenation of nitro and carbonyl substrates have been synthesized. All iridium complexes showed efficient catalytic activity for the hydrogenation of ketones, aldehydes, and nitro-containing compounds using clean H₂ as reducing reagent. The iridium catalyst displayed the highest TON values of 960 and 950 in the hydrogenation of carbonyl and nitro substrates, respectively. Various types of substrates with different substituted groups afforded corresponding products in excellent yields. All N,O-coordinate iridium(III) complexes 1-4 were well characterized by IR, NMR, HRMS, and elemental analysis. The molecular structure of complex 1 was further characterized by single-crystal X-ray determination.

An Imidazole Thione-Modified Polyhedral Oligomeric Silsesquioxane for Selective Detection and Adsorptive Recovery of Au(III) from Aqueous Solutions

Developing a material toward simultaneous detection and recovery of gold ions (Au(III)) is highly desirable for the economy and the environment. Herein, we report a highly efficient dual-function material for simultaneous Au(III) detection and recovery by simply introducing abundant imidazole thione and thioether groups in one system. This material, that is, an imidazole thione-modified polyhedral oligomeric silsesquioxane (POSS-2), was prepared by a mild reaction of an imidazolium-containing POSS and sulfur at ambient temperature. The POSS-2 suspension in water can rapidly and selectively detect Au(III) with a very low limit of detection of 1.2 ppb by fluorescence quenching or a visualized color change from white to dark orange. POSS-2 can also selectively and efficiently capture Au(III) with a maximum adsorption uptake of 1486.5 mg/g. The adsorption process well fits with the pseudo-second-order kinetic and Langmuir models. The intriguing dual-function performance is better than most of the previous Au(III) probes or adsorbents. The mechanism study reveals that the detection and adsorption behavior are mainly caused by the redox reaction and coordination between imidazole thione and thioether groups and Au(III). Furthermore, POSS-2 was successfully utilized to extract gold without interference from a discard CPU. These results indicate the potential application of the present dual-function material for Au(III) detection and recovery from aqueous solutions. More dual-functional materials could be designed and prepared by this simple strategy.

Increased Recovery of Gold Thiosulfate Alkaline Solutions by Adding Thiol Groups in the Porous Structure of Activated Carbon

Thiosulfate leaching combined with ion-exchange resins is an innovative alternative for gold recovery. According to the properties of activated carbon, it could replace resins in the gold recovery process, improve efficiency, and reduce operating cost. In this research, the adsorption process of gold thiosulfate complex on thiol-modified activated carbon was studied. Thioglycolic acid (ATG) was impregnated in activated carbon, and its adsorption ability was tested with synthetic solutions of gold and sodium thiosulfate (Au 10 mg·L^-1, Na₂S₂O₃ 0.1 mol·L^-1, pH = 10.0). Carbon was characterized by infrared spectroscopy, SEM-EDS, PZC titration, hardness number measures, and proximal analysis. Synthetic solutions were also characterized by UV-vis spectroscopy and cyclic voltammetry. The percentage of volatile material increased from 10.0 to 13.9% due to the impregnation process of ATG. Infrared spectra show characteristic bands of C-H, S-H, and C-S bonds. In the adsorption tests, the ATG-impregnated carbon achieved 91% of gold recovery, while the same amount of ATG in the liquid phase stirred with unmodified activated carbon reached 90% of gold recovery. The 44.9% of gold recovered with activated carbon impregnated with ATG was eluted with sodium cyanide ([NaCN] = 0.2 mol·L^-1; [NaOH] = 0.25 mol·L^-1; [CH₃CH₂OH] = 30% V/V; pH = 12.0; t = 24 h). These results suggest the gold transferred from the thiosulfate complex to a new gold thiolate complex.

Biomolecule-Mediated Generation of Ru Nanocatalyst for Sustainable Reduction of Nitrobenzene

A mild and sustainable synthetic route was followed for the generation of biomolecule-assisted Ru nanocatalyst under open as well as inert atmosphere using the polyphenol morin. The nanocatalyst was characterized thoroughly by powder X-ray diffraction, N₂ adsorption-desorption, high-resolution transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, absorption spectroscopy, Fourier transform infrared spectroscopy, fluorescence spectroscopy, thermogravimetric analysis, and inductively coupled plasma optical emission spectrometry. The nanocatalyst reveals excellent catalytic activity for the reduction of several substituted nitrobenzene to aniline derivatives under simple, mild, and environment-friendly conditions. The catalyst can be reused for four consecutive cycles without significant loss in its catalytic activity.

N-Heterocyclic Carbene Adducts of Main Group Elements and Their Use as Ligands in Transition Metal Chemistry

N-Heterocyclic carbenes (NHC) are nowadays ubiquitous and indispensable in many research fields, and it is not possible to imagine modern transition metal and main group element chemistry without the plethora of available NHCs with tailor-made electronic and steric properties. While their suitability to act as strong ligands toward transition metals has led to numerous applications of NHC complexes in homogeneous catalysis, their strong σ-donating and adaptable π-accepting abilities have also contributed to an impressive vitalization of main group chemistry with the isolation and characterization of NHC adducts of almost any element. Formally, NHC coordination to Lewis acids affords a transfer of nucleophilicity from the carbene carbon atom to the attached exocyclic moiety, and low-valent and low-coordinate adducts of the p-block elements with available lone pairs and/or polarized carbon-element π-bonds are able to act themselves as Lewis basic donor ligands toward transition metals. Accordingly, the availability of a large number of novel NHC adducts has not only produced new varieties of already existing ligand classes but has also allowed establishment of numerous complexes with unusual and often unprecedented element-metal bonds. This review aims at summarizing this development comprehensively and covers the usage of N-heterocyclic carbene adducts of the p-block elements as ligands in transition metal chemistry.

Catalytic hydrogenation of carbonyl and nitro compounds using an [N,O]-chelate half-sandwich ruthenium catalyst

A series of N,O-chelate half-sandwich ruthenium complexes have been synthesized, which exhibited high activity for the catalytic hydrogenation of carbonyl and nitro compounds in aqueous solution.

NHCs in Main Group Chemistry

Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC-main group element adducts, and might be useful for the broad research community.

Where does Au coordinate to N-(2-pyridiyl)benzotriazole: gold-catalyzed chemoselective dehydrogenation and borrowing hydrogen reactions

Pyridyltriazole gold(i) complexes proved to be an efficient precatalyst for the most challenging gold-catalyzed borrowing hydrogen reaction and dehydrogenation of alcohols and amines.

Palladium pincer-type complexes and zwitterionic sulfur adducts of pyridine-bridged bis(1,2,3-triazolin-5-ylidenes): syntheses, characterizations and catalytic applications

Different reactivities of pincer-type pyridine-bridged bis(mesoionic carbenes) towards palladium(ii) and elemental sulfur have been revealed.

Stabilisation of gold nanoparticles by N-heterocyclic thiones

Gold nanoparticles (Au-NPs) have been prepared using N-heterocyclic thiones (NHTs) as ligand stabilisers.

Large CuI8 chalcogenone cubic cages with non-interacting counter ions

Synthesis and applications of two mega size octanuclear copper(i) chalcogenone cages have been reported.

Half-sandwich cycloruthenated complexes from aryloxazolines: synthesis, structures, and catalytic activities

The half-sandwich cycloruthenated complexes [Ru(p-cymene)LCl] show promising catalytic activity in nitroarene reduction.

An easily accessible and recyclable copper nanoparticle catalyst for the solvent-free synthesis of dipyrromethanes and aromatic amines

A facile method to prepare a reusable copper nanocatalyst is reported.

Characterisation of gold catalysts

Au-based catalysts have established a new important field of catalysis, revealing specific properties in terms of both high activity and selectivity for many reactions.