Decoding the Catalytic Potential of Dinuclear 1-Row Transition Metal Complexes for Proton Reduction and Water Oxidation.

The growing interest in renewable energy sources has led to a significant focus on artificial photosynthesis as a means of converting solar energy into lucrative and energy-dense carbonaceous fuels. First-row transition metals have thus been brought to light in the search for efficient and high-performance homogenous molecule catalysts that can accelerate energy transformation and reduce overpotentials during the catalytic process. Their dinuclear complexes have opportunities to enhance the efficiency and stability of these molecular catalysts, primarily for the hydrogen evolution reaction (HER) and water oxidation reaction (WOR).

Harnessing Ruthenium and Copper Catalysts for Formate Dehydrogenase Reactions.

Formic acid (HCOOH) is a promising source of hydrogen energy that can be used to produce hydrogen in a more economical and ecological way. Formic acid is a simple carboxylic acid with a high hydrogen concentration and is generally stable, making it useful as a hydrogen transporter. Catalytic dehydrogenation is usually used to extract hydrogen from formic acid; this process releases hydrogen gas and yields carbon dioxide as a byproduct.

Physicochemical Analysis of Cu(II)-Driven Electrochemical CO Reduction and its Competition with Proton Reduction.

The reduction of CO has become a key role in reducing greenhouse gas emissions in efforts to search for long-term responses to climate change. We report a couple of CO-reducing molecular catalysts based on earth-abundant copper complexes. These are [Cu(DPA)(PyNAP)] (1) and [Cu(DPA)(PyQl)] (2) (where, DPA=pyridine-2,6-dicarboxylate, PyNAP=2-(pyridin-2-yl)-1,8-naphthyridine, and PyQl=2-(pyridin-2-yl)quinoline).

Tuning Pd-to-Ag Ratio to Enhance the Synergistic Activity of Fly Ash-Supported PdAg Bimetallic Nanoparticles.

Fly ash (FA)-supported bimetallic nanoparticles (PdAg/FA) with varying Pd:Ag ratios were prepared by coprecipitation of Pd and Ag involving in situ reduction of Pd(II) and Ag(I) salts in aqueous medium. All the supported nanoparticles were thoroughly characterized with the aid of powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), electron microscopy (field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM)), and elemental analyses, which include inductively coupled plasma-optical emission spectroscopy (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS). A gradual broadening and shifting of PXRD peaks, ascribable to Ag, to higher angles with an increase in the Pd:Ag ratio affirms the alloying of interface between Pd and Ag nanoparticles.

Formate dehydrogenase activity by a Cu(II)-based molecular catalyst and deciphering the mechanism using DFT studies.

Due to the requirement to establish renewable energy sources, formic acid (FA), one of the most probable liquid organic hydrogen carriers (LOHCs), has received great attention. Catalytic formic acid dehydrogenation in an effective and environmentally friendly manner is still a challenge. The N3Q3 ligand (N3Q3 = ,-bis(quinolin-8-ylmethyl)quinolin-8-amine) and the square pyramidal [Cu(N3Q3)Cl]Cl complex have been synthesised in this work and characterised using several techniques, such as NMR spectroscopy, mass spectrometry, EPR spectroscopy, cyclic voltammetry, X-ray diffraction and DFT calculations.

Electrocatalytic hydrogen evolution by a dinuclear copper complex and mechanistic elucidation through DFT studies.

A novel dinuclear copper complex, [CuII2(L1)2] (L1 = 2-{[2-(8-hydroxyquinolin-2-yl)-1-benzimidazol-1-yl]methyl}quinolin-8-ol) was synthesised and characterised through various spectroscopic techniques. This dinuclear complex (as an electrocatalyst) was employed to examine the catalytic ability towards an electrochemical hydrogen evolution reaction (HER). Redox studies in 95/5 (v/v) DMF/HO with the addition of 30-equivalent AcOH (acid source) led to higher catalytic activities for the HER.

Ligand-Mediated Hydrogen Evolution by Co(II) Complexes and Assessment of the Mechanism by Computational Studies.

In this work, two novel dinuclear cobalt complexes, [] () and [] (), featuring benzimidazole derived redox-active ligand have been synthesized to investigate their catalytic activities toward electrocatalytic proton reduction (where is 2-{[6-chloro-2-(8-hydroxyquinolin-2-yl)-1-benzimidazol-1-yl]methyl}quinolin-8-ol and is 2-{[6-nitro-2-(8-hydroxyquinolin-2-yl)-1-benzimidazol-1-yl]methyl}quinolin-8-ol). The electrochemical responses in 95/5 (v/v) DMF/HO with the addition of 24 equiv of AcOH as a proton source manifest high catalytic activity for proton reduction to H. The catalytic reduction event yields H at an applied potential of -1.

Redox-Induced Structural Switching through Sporadic Pyridine-Bridged CoCo Dimer and Electrocatalytic Proton Reduction.

The homodinuclear Co helicate complex [Co(DQPD)] () was prepared by treating [Co(HO)](ClO) with the deprotonated form of the ligand ,-bis(quinolin-8-yl)pyridine-2,6-dicarboxamide (DQPDH). Complex represents a discrete homodinuclear helicate complex with two Co centers having a distorted-octahedral geometry through an unprecedented pyridine bridge. Complex , upon treatment with HO, undergoes oxidation at one of the Co centers followed by a structural deformation to generate the mixed-valence complex [CoCo(DQPD)](ClO) ().

Fabrication of a Hierarchical TiO₂ Microsphere/Carbon Dots Photocatalyst for Oxygen Evolution and Dye Degradation Under Visible Light.

Anatase hierarchical TiO2 microsphere/carbon dots composite (HTM/CDs) was fabricated by a facile method for active visible light photocatalysis. The phase, morphology, microstructure and optical properties were investigated by X-ray diffraction, scanning electronmicroscopy, transmission electron microscopy and UV-VIS diffuse reflectance spectroscopy respectively. Under visible light illumination, the fabricated HTM/CDs composite was exhibited an enhanced photo catalytic activity compared to that of pure hierarchical TiO2 microspheres (HTM).

μ-Pyridine-bridged copper complex with robust proton-reducing ability.

The binuclear copper complex [Cu(DQPD)]2 (where DQPD = deprotonated N,N-di(quinolin-8-yl)pyridine-2,6-dicarboxamide (DQPDH2)) was synthesised and characterised by various spectroscopic as well as electrochemical techniques. The binuclear copper complex was converted into a mononuclear one by the addition of 2 equivalents of pTsOH into [Cu(DQPD)]2. The interconversion between the dimer and monomer complex was studied through UV-Vis spectroscopy and cyclic voltammetry.

Proton reduction by a nickel complex with an internal quinoline moiety for proton relay.

The complex Ni(DQPD) (where DQPD = deprotonated N(2),N(6)-di(quinolin-8-yl)pyridine-2,6-dicarboxamide (DQPDH2)) behaves as a visible light driven active catalyst to reduce protons from water when employed with the photosensitizer fluorescein (Fl) and triethylamine (TEA) as the sacrificial electron donor. The photocatalytic system shows very high activity, attaining 2160 turnovers and an initial turnover rate of 0.032 s(-1) with respect to the catalyst.

[Ru(NCN-Me)(bpy)(=O)] Mediates efficient C–H bond oxidation from NADH analogs in aqueous media rather than water oxidation.

[Ru(V)[double bond, length as m-dash]O](3+) and [Ru(VI)[double bond, length as m-dash]O](4+) generated from [Ru(II)(NCN-Me)(bpy)(H2O)](PF6)2 (where NCN-Me is the neutral N-methyl-3,5-di(2-pyridyl)pyridinium iodide after deprotonation of the C-H bond) play a selective role in the C-H bond oxidation of 2-(pyridin-2-yl)-9,10-dihydroacridine (PADHH) and water oxidation, respectively.

Comparative study of C^N and N^C type cyclometalated ruthenium complexes with a NAD+/NADH function.

Cyclometalated ruthenium complexes having C(^)N and N(^)C type coordinating ligands with NAD(+)/NADH function have been synthesized and characterized by spectroscopic methods. The variation of the coordinating position of σ-donating carbon atom leads to a drastic change in their properties. Both the complex Ru(phbn)(phen)(2)]PF(6) ([1]PF(6)) and [Ru(pad)(phen)(2)]PF(6) ([2]PF(6)) reduced to Ru(phbnHH)(phen)(2)]PF(6) ([1HH]PF(6)) and [Ru(padHH)(phen)(2)]PF(6) ([2HH]PF(6)) by chemical and electrochemical methods.

Photoisomerization and proton-coupled electron transfer (PCET) promoted water oxidation by mononuclear cyclometalated ruthenium catalysts.

Photoisomeric transformations in ruthenium polypyridyl complexes have been rarely reported. Herein we report the geometrical transformation of cyclometalated trans-[Ru(tpy)(PAD)(OH(2))](+) ([1](+)) to the cis-[Ru(tpy)(PAD)(OH(2))](+) ([1a](+)) (tpy = 2,2';6',2"-terpyridine, PAD = 2-(pyrid-2'-yl)acridine) isomer upon irradiation of visible light (λ ≥420 nm). Due to a proton-induced tautomeric equilibrium between the Ru-C bond and Ru═C coordination, the π* energy levels of PADH are lower than those of tpy by 12.

Photo- and electrochemical redox behavior of cyclometalated Ru(II) complexes having a 3-phenylbenzo[b][1,6]naphthyridine ligand.

Cyclometalated Ru(II) complexes having a 3-phenylbenzo[b][1,6]naphthyridine (phbn) ligand have been synthesized and characterized by spectroscopic methods. The photo- and electrochemical redox behavior of the complexes are demonstrated. Complex [Ru(phbn)(bpy)(2)]PF(6) ([1]PF(6)) readily undergoes proton coupled two electron reduction by chemical, electrochemical, and photochemical methods to generate [Ru(phbnHH)(bpy)(2)]PF(6) ([1HH]PF(6)).

Proton-induced dynamic equilibrium between cyclometalated ruthenium rNHC (remote N-heterocyclic carbene) tautomers with an NAD+/NADH function.

Cyclometalated ruthenium(II) complexes having acridine moieties have been synthesized and characterized by spectroscopic methods. Protonation of the acridine nitrogen of the ruthenium(II) complexes not only causes dynamic equilibrium with remote N-heterocyclic carbene Ru═C complexes but also generates the NAD(+)/NADH redox function driven by a proton-coupled two-electron transfer accompanying a reversible C-H bond formation in the pyridinium ring.

Cu(NO3)2.3H2O-mediated synthesis of 4'-(2-pyridyl)-2,2':6',2' '-terpyridine (L2) from N-(2-pyridylmethyl)pyridine-2-methylketimine (L1). A C-C bond-forming reaction and the structure of {[Cu(L2)(OH)(NO3)][Cu(L2)(NO3)2]}.2H2O.

N-(2-Pyridylmethyl)pyridine-2-methylketimine (L1) was synthesized from equimolar quantities of (2-pyridyl)methylamine and 2-acetylpyridine. Methanolic solution of L1 reacted readily with Cu(NO3)2.3H2O in air, affording green solid of composition {[Cu(L2)(OH)(NO3)][Cu(L2)(NO3)2]}.