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Multifunctional heterogeneous catalysts are an effective strategy to drive chemical cascades, with attendant time, resource and cost efficiencies by eliminating unit operations arising in normal multistep processes. Despite advances in the design of such catalysts, the fabrication of proximate, chemically antagonistic active sites remains a challenge for inorganic materials science. Hydrogen‐bonded organocatalysts offer new opportunities for the molecular level design of multifunctional structures capable of stabilising antagonistic active sites. We report the catalytic application of a charge‐assisted, hydrogen‐bonded crystalline material, bis(melaminium)adipate (BMA), synthesised from melamine and adipic acid, which possesses proximate acid‐base sites. BMA exhibits high activity for the cascade deacetalisation‐Knoevenagel condensation of dimethyl acetals to form benzylidenemalononitriles under mild conditions in water; BMA is amenable to large‐scale manufacture and recycling with minimal deactivation. Computational modelling of the melaminium cation in protonated BMA explains the observed catalytic reactivity, and identifies the first demethoxylation step as rate‐limiting, which is in good agreement with time‐dependent 1H NMR and kinetic experiments. A broad substrate scope for the cascade transformation of aromatic dimethyl acetals is demonstrated. [ABSTRACT FROM AUTHOR]

Membrane-targeting compounds are of immense interest to counter complicated multi-drug resistant infections. However, the broad-spectrum effect of such compounds is often unmet due to the surges of antibiotic resistance among majority of Gram-negative bacteria compared to Gram-positive species. Though amphiphiles, synthetic mimics of antimicrobial peptides etc, have been extensively explored for their potential to perturb bacterial membranes, small molecule-based supramolecular hydrogels have remained unexplored. The design of supramolecular hydrogels can be tuned on-demand, catering to desired applications, including facile bacterial membrane perturbation. Considering the strong biocidal properties of Ag-based systems and the bacterial membrane-targeting potential of appended primary amine groups, we designed self-assembled multicomponent supramolecular Ag(I)-hydrogels with urea and DATr (3,5-diamino-1,2,4-triazole) as ligands, which are predisposed for hydrogen bonding and interacting with negatively charged bacterial membranes at physiological pH. The synthesized supramolecular Ag(I)-hydrogels exhibited almost similar antibacterial activity against both Gram-negative (Campylobacter jejuni; C. jejuni) and Gram-positive (Staphylococcus aureus; S. aureus) bacteria, with minimal inhibitory concentration (MIC) of ∼60 μg mL−1. Ag(I)-hydrogels facilitated the disruption of the negatively charged bacterial membrane due to electrostatic interaction and complementary hydrogen bonding facilitated by DATr and urea. Sustained intracellular ROS generation in the presence of Ag(I)-hydrogel further expedited cell lysis. We envisage that the multicomponent supramolecular Ag(I)-hydrogels studied herein can be employed in designing effective antibacterial coatings on a range of medical devices, including surgical instruments. Moreover, the present form of the hydrogels has the potential to improve the antibacterial functionality of conventional antimicrobials, thus revitalizing the effective targeting of hard-to-treat multi-drug-resistant (MDR) bacterial infections in a clinical set up. [ABSTRACT FROM AUTHOR]

A series of Ag(I) supramolecular organo-aqueous gels have been synthesized in the presence of an amine-rich triazole ligand as a gelator. Judicious choice of the triazole derivative and counter anion allows a desired spatial orientation of the pendant amine functionality to accentuate the gelation ability and autonomous self-healability via hydrogen bonding. In addition, the hydrogen bond donors, i.e. pendant –NH2 groups, offer a critical proximity of counter anions to the Lewis acidic Ag(I) and the reactants for promoting a three component coupling reaction of an aldehyde, a terminal alkyne and an amine, giving expedient access to propargyl amines, with remarkable functional group tolerance for both aromatic and aliphatic aldehydes, and aryl acetylenes. Experiments substantiate the pivotal role of counter anions and H-bonding interactions in the observed preference for propargylamines over the diacetylene by-product. Our catalyst is robust, bench-stable, and recyclable, and demonstrates a catalytic efficiency comparable to or better than those of reported systems. The catalyst was found equally effective for the gram-scale synthesis of propargylamines. Our approach lies at the intersection of metal-based, H-bond-mediated counter anion-tuned catalysis, evincing a potential for the development of purpose-built supramolecular gels for desired catalytic applications in the future. [ABSTRACT FROM AUTHOR]

Urban mining of e-waste, especially end-of-life lithium ion batteries (LIBs), is gaining momentum as a potential secondary source for valuable metals and due to the environmental impact associated with their disposal. Utilization of these metals in renewable energy-related applications could cater to the realization of a circular economy by reusing industrial waste for sustainable applications. In this regard, we explore the formation of Ni3+-enriched β-Ni(OH)2 from spent LIBs and analyze its efficacy as an electrocatalyst for the oxygen evolution reaction (OER). As-synthesized β-Ni(OH)2 requires a minimal overpotential of 300 mV to reach a current density of 50 mA cm−2 with a low Tafel slope of 42.7 mV dec−1. The usual sluggish kinetics of the OER is mitigated due to the strategic presence of a small amount of NiOOH, and surface oxygen vacancies. In situ impedance analysis strongly supports the improved OER performance of Ni3+-rich β-Ni(OH)2 due to facile OH* adsorption followed by rapid charge transfer at the electrode–electrolyte interface. The combined effect is manifested in ultrafast OER with mass activity 1044 mA mg−1 and TOF 257.2 s−1, which are exceptional for Ni-containing systems. The structural integrity of the catalyst was validated with post-OER characterization experiments, delineating the applicability of e-waste-derived materials for renewable energy applications. [ABSTRACT FROM AUTHOR]

A new electron, six-electron, sulfide-bicapped trinuclear [Mo.sup.IV] cluster containing all sulfur coordination where each Mo atom is seven coordinated and retains the oxidation state of +14 is described. The formation of a binuclear tungsten(V) complex under identical reaction conditions with one electron oxidation of each [W.sup.IV] center and the redox chemistry of these complexes are rationalized.

This study describes the characterization of a mixed-valence RuII/NiI complex, a structural model for the Ni-L state of the [NiFe]hydrogenases. One-electron oxidation of (cymene)Ru(μ-pdt)Ni(diphos) ([1]0, diphos = dppe, C2H4(PPh2)2; [2]0, diphos = dcpe, C2H4(P(C6H11)2)2] affords the mixed-valence cations [(cymene)Ru(pdt)Ni(diphos)]+ ([1]+ and [2]+). Crystallographic and spectroscopic measurements indicate that these cations are described as RuII/NiI. Although [1]0 and [1]+ are very similar structurally, the following changes are notable: the Ni-P distances elongate upon oxidation, and the Ru-Ni distance changes insignificantly. The molecular and electronic structures of the Ni center in [1]+ approaches that observed in the [NiFe]hydrogenases. Density functional theory calculations indicate that [1]0 is best described as RuII/Ni0, consistent with its oxidation to RuII/NiI in [1]+. The fast electron self-exchange rate of 107 M-1 s-1 between [1]0 and [1]+ suggests minor reorganization, more consistent with a Ni0/NiI oxidation state change than a NiI/NiII couple. In solution, [1]+ slowly converts to [H1]+ and [1-H]+, with the latter being a complex of the thioaldehyde SCHCH2CH2S arising from C-H activation of the pdt backbone. Treatment of [1]+ with the H-atom abstracting reagent 2,2,6,6-tetramethylpiperidine-1-oxy also gives [1-H]+. [ABSTRACT FROM AUTHOR]

Electrocatalytic nitrogen fixation to ammonia (NH 3 ), a precursor for fertilizer production and a promising energy carrier, has garnered widespread interest as an environment-friendly and sustainable alternative to the energy-intensive fossil-feedstock-dependent Haber-Bosch process. The large-scale deployment of this process is contingent on the identification of inexpensive, Earth-abundant systems that can operate efficiently, irrespective of the electrolyte pH for the selective production of NH 3 . In this regard, we discuss the scalable synthesis of VO 2 anchored on N-doped carbon (VO2@CN), and its applicability as a robust electrocatalyst for the nitrogen reduction reaction (NRR). Benefitting from the presence of exposed VO 2 , which presumably acts as the active site for nitrogen reduction, and its activity over a broad pH range (from acidic to neutral), VO2@CN exhibits a high NH 3 yield of 0.31 and 0.52 μmol h -1 mg cat -1 and a maximum Faradaic efficiency (FE) of 67.9% and 61.9% at -0.1 V vs . RHE, under neutral and acidic conditions, respectively. The obscured reaction intermediates of the NRR were identified from in situ ATR-IR studies under both electrolyte conditions. Additionally, the high selectivity of the catalyst was ascertained from the absence of hydrazine production and the competing hydrogen evolution reaction (HER). However, ammonia production underwent a reduction over 12 h of continuous operation presumably owing to the leaching of catalyst under these electrolysis conditions, which was more pronounced in electrolytes with acidic pH. Overall, the present report unveils the performance of an earth-abundant vanadium oxide-based system as an efficient electrocatalyst for the NRR under acidic and neutral pH conditions.

Metallogels formed from supramolecular interactions of low-molecular-weight gelators (LMWGs) combine the qualities of heterogeneous catalysts and offer the advantages of multifunctionality owing to the facile installation of desired task-specific moieties on the surface and along the channels of the gels. We discuss the applications of a triazole-based Ni(II) gel-derived xerogel ( NiXero ) having a high density of Ni(II)-nodes and appended primary amines as a recyclable heterogeneous catalyst for Knoevenagel condensation of aldehyde and malononitrile in water and the solvent-free cycloaddition of CO 2 to form a series of cyclic carbonates with near-quantitative conversion of the respective epoxides, with low catalyst loading (0.59 mol %), high catalyst stability, and recyclability. The structural advantages of NiXero , due to the concurrent presence of bifunctional Lewis acid-base sites on the channels, open Ni(II) nodes, N triazole , pendant -NH 2 and its chemical stability, are conducive to the cooperative heterogeneous catalytic activity under mild conditions. This work emphasizes the effective amalgamation of metals with purpose-built ligand systems for the construction of metallogels and their utility as heterogeneous catalysts for desired organic transformations.

The cleavage of C-O bonds in lignin model compounds without hydrogen was developed using the commercially available Pd/C. Hydrogen donor solvents are helpful for this reaction through transfer hydrogenation, but not necessary. A redox neutral process that utilizes the internal hydrogen source for the cleavage is also possible. An initial mechanistic study indicates that the β-benzylic-H atom in the substrate plays a critical role and that the present system undergoes a process different from previous reports., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)