Disulfide Bond Accelerated Transesterification in Poly(ß-hydrazide disulfide esters) toward Fast Network Rearrangements.

The development of catalyst-free ester-based covalent adaptable networks (CANs) provides a new approach to achieve milder reaction conditions to reprocess thermoset resins. Despite recent advances, however, accelerating network rearrangements requires the introduction of hydroxyl groups into the network. In this study, disulfide bonds are introduced into the CANs to add new kinetically facile pathways to accelerate network rearrangement. Kinetic experiments using small molecule models of the CANs show that the presence of the disulfide bonds can accelerate transesterification. These insights are applied to synthesize new kinds of poly(ß-hydrazide disulfide esters) (PSHEs) using thioctic acyl hydrazine (TAH) as a precursor for ring-opening polymerization with the hydroxyl-free multifunctional acrylates. The PSHE CANs have lower relaxation times (505-652 s) than the polymer containing only ß-hydrazide esters (2903 s). The ring-opening polymerization of TAH improves the crosslinking density, heating resistance deformation temperature, and UV shielding performance of the PSHEs. Thus, this work provides a practical strategy to reduce the reprocessing temperatures of CANs.

Visible Light Driven Hydrogen Evolution by Molecular Nickel Catalysts with Time-Resolved Spectroscopic and DFT Insights.

Hydrogen (H2) is a clean fuel that can potentially be a future solution for the storage of intermittent renewable energy. However, current H2 production is mainly dominated by the energy intensive steam reforming reaction, which consumes a fossil fuel, methane, and emits copious amounts of carbon dioxide as one of the byproducts. To address this challenge, we report a molecular catalyst that produces H2 from aqueous solutions, is composed of affordable, earth-abundant elements such as nickel, and has been incorporated into a system driven by visible light. Under optimized conditions, we observe a turnover number of 3880, among the best for photocatalytic H2 evolution with nickel complexes from water-methanol solutions. Through nanosecond transient absorption, electron paramagnetic resonance, and UV-vis spectroscopic measurements, and supported by density functional theory calculations, we report a detailed study of this photocatalytic H2 evolution cycle. We demonstrate that a one-electron reduced, predominantly ligand-centered, reactive Ni intermediate can be accessed under visible light irradiation using triethylamine as the sacrificial electron donor and reductive quencher of the initial photosensitizer excited state. In addition, the computational calculations suggest that the second coordination sphere ether arms can enhance the catalytic activity by promoting proton relay, similar to the mechanism among [FeFe] hydrogenases in nature. Our study can form the basis for future development of H2 evolution molecular catalysts that incorporate both ligand redox noninnocence and alternative second coordination sphere effects in artificial photosynthetic systems driven by visible light.

Hydrophobic Metal Halide Perovskites for Visible-Light Photoredox C-C Bond Cleavage and Dehydrogenation Catalysis.

Two-dimensional lead and tin halide perovskites were prepared by intercalating the long alkyl group 1-hexadecylammonium (HDA) between the inorganic layers. We observed visible-light absorption, narrow-band photoluminescence, and nanosecond photoexcited lifetimes in these perovskites. Owing to their hydrophobicity and stability even in humid air, we applied these perovskites in the decarboxylation and dehydrogenation of indoline-2-carboxylic acids. (HDA)2 PbI4 or (HDA)2 SnI4 were investigated as photoredox catalysts for these reactions, and quantitative conversion and high yields were observed with the former.

Synthesis and the Optical and Electrochemical Properties of Indium(III) Bis(arylimino)acenaphthene Complexes.

Aryl bis(imino)acenaphthenes (Ar-BIANs) are well-established rigid and sterically bulky diimine ligands, which are redox-noninnocent and versatile π-acceptors due to their low-lying π* orbitals and are frequently used to bind transition metals. However, the coordination chemistry of Ar-BIAN ligands to main group elements is not as well-developed as that of their transition metal counterparts. In particular, there are no comprehensive studies describing the spectroscopic and electrochemical properties of main group Ar-BIAN complexes. Herein, we report the synthesis and full characterization of a series of new indium(III) Ar-BIAN complexes, bearing 2,6-dialkyl (1b and 2b), 4-nitro (3b), and 4-dimethylamino (4b) groups at the aryl-diimine part of the ligand. Their optical and electrochemical properties have been revealed by UV-vis spectroscopy and cyclic voltammetry, respectively. Additionally, DFT calculations were performed to gain insights into the nature of the properties displayed.

Understanding the Origins of Nucleophilic Hydride Reactivity of a Sodium Hydride-Iodide Composite.

Sodium hydride (NaH) has been commonly used as a Brønsted base in chemical syntheses, while it has rarely been employed to add hydride (H(-) ) to unsaturated electrophiles. We previously developed a procedure to activate NaH through the addition of a soluble iodide source and found that the new NaH-NaI composite can effect even stereoselective nucleophilic hydride reductions of nitriles, imines, and carbonyl compounds. In this work, we report that mixing NaH with NaI or LiI in tetrahydrofuran (THF) as a solvent provides a new inorganic composite, which consists of NaI interspersed with activated NaH, as revealed by powder X-ray diffraction, and both solid-state NMR and X-ray photoelectron spectroscopies. DFT calculations imply that this remarkably simple inorganic composite, which is comprised of NaH and NaI, gains nucleophilic hydridic character similar to covalent hydrides, resulting in unprecedented and unique hydride donor chemical reactivity.

Protocol for photocatalytic upcycling of non-biodegradable plastics into platform chemicals at ambient conditions.

Upcycling plastics presents an opportunity not only to reduce plastic waste, but also to provide an alternative carbon source to fossil fuels. Herein, we present a protocol to upcycle plastics with resin codes 2-7 using a commercially available base-metal photocatalyst. We first conducted batch reactions, followed by a continuous, segmented flow system for gram-scale upcycling into value-added platform chemicals. This protocol, employing tandem carbon-hydrogen bond oxidation/carbon-carbon bond cleavage reactions, can be useful for photocatalytically transforming plastics at ambient conditions. For complete details on the use and execution of this protocol, please refer to Li et al. (2023).1.

Machine-Learning-Assisted Discovery of Mechanosynthesized Lead-Free Metal Halide Perovskites for the Oxidative Photocatalytic Cleavage of Alkenes.

Lead-free metal halide perovskites can potentially be air- and water-stable photocatalysts for organic synthesis, but there are limited studies on them for this application. Separately, machine learning (ML), a critical subfield of artificial intelligence, has played a pivotal role in identifying correlations and formulating predictions based on extensive datasets. Herein, an iterative workflow by incorporating high-throughput experimental data with ML to discover new lead-free metal halide perovskite photocatalysts for the aerobic oxidation of styrene is described. Through six rounds of ML optimization guided by SHapley Additive exPlanations (SHAP) analysis, BA2CsAg0.95Na0.05BiBr7 as a photocatalyst that afforded an 80% yield of benzoic acid under the standard conditions is identified, which is a 13-fold improvement compared to the 6% with when using Cs2AgBiBr6 as the initial photocatalyst benchmark that is started. BA2CsAg0.95Na0.05BiBr7 can tolerate various functional groups with 22 styrene derivatives, highlighting the generality of the photocatalytic properties demonstrated. Radical scavenging studies and density functional theory calculations revealed that the formation of the reactive oxygen species superoxide and singlet oxygen in the presence of BA2CsAg0.95Na0.05BiBr7 are critical for photocatalysis.

Recent Advances in Defect-Engineered Transition Metal Dichalcogenides for Enhanced Electrocatalytic Hydrogen Evolution: Perfecting Imperfections.

Switching to renewable, carbon-neutral sources of energy is urgent and critical for climate change mitigation. Despite how hydrogen production by electrolyzing water can enable renewable energy storage, current technologies unfortunately require rare and expensive platinum group metal electrocatalysts, which limit their economic viability. Transition metal dichalcogenides (TMDs) are low-cost, earth-abundant materials that possess the potential to replace platinum as the hydrogen evolution catalyst for water electrolysis, but so far, pristine TMDs are plagued by poor catalytic performances. Defect engineering is an attractive approach to enhance the catalytic efficiency of TMDs and is not subjected to the limitations of other approaches like phase engineering and surface structure engineering. In this minireview, we discuss the recent progress made in defect-engineered TMDs as efficient, robust, and low-cost catalysts for water splitting. The roles of chalcogen atomic defects in engineering TMDs for improvements to the hydrogen evolution reaction (HER) are summarized. Finally, we highlight our perspectives on the challenges and opportunities of defect engineering in TMDs for electrocatalytic water splitting. We hope to provide inspirations for designing the state-of-the-art catalysts for future breakthroughs in the electrocatalytic HER.

Visible light-induced hole injection into rectifying molecular wires anchored on Co3O4 and SiO2 nanoparticles.

Tight control of charge transport from a visible light sensitizer to a metal oxide nanoparticle catalyst for water oxidation is a critical requirement for developing efficient artificial photosynthetic systems. By utilizing covalently anchored molecular wires for hole transport from sensitizer to the oxide surface, the challenge of high rate and unidirectionality of the charge flow can be addressed. Functionalized hole conducting molecular wires of type p-oligo(phenylenevinylene) (3 aryl units, abbreviated PV3) with various anchoring groups for the covalent attachment to Co(3)O(4) catalyst nanoparticles were synthesized and two alternative methods for attachment to the oxide nanoparticle surface introduced. Covalent anchoring of intact PV3 molecules on Co(3)O(4) nanoparticles (and on SiO(2) nanoparticles for control purposes) was established by FT-Raman, FT-IR, and optical spectroscopy including observation, in some cases, of the vibrational signature of the anchored functionality. Direct monitoring of the kinetics of hole transfer from a visible light sensitizer in aqueous solution ([Ru(bpy)(3)](2+) (and derivatives) light absorber, [Co(NH(3))(5)Cl](2+) acceptor) to wire molecules on inert SiO(2)(12 nm) particles by nanosecond laser absorption spectroscopy revealed efficient, encounter controlled rates. For wire molecules anchored on Co(3)O(4) nanoparticles, the recovery of the reduced sensitizer at 470 nm indicated similarly efficient hole transfer to the attached PV3, yet no transient hole signal was detected at 600 nm. This implies hole injection from the anchored wire molecule into the Co(3)O(4) particle within 1 µs or shorter, indicating efficient charge transport from the visible light sensitizer to the oxide catalyst particle.

Upcycling to Sustainably Reuse Plastics.

Plastics are now indispensable in daily lives. However, the pollution from plastics is also increasingly becoming a serious environmental issue. Recent years have seen more sustainable approaches and technologies, commonly known as upcycling, to transform plastics into value-added materials and chemical feedstocks. In this review, the latest research on upcycling is presented, with a greater focus on the use of renewable energy as well as the more selective methods to repurpose synthetic polymers. First, thermal upcycling approaches are briefly introduced, including the redeployment of plastics for construction uses, 3D printing precursors, and lightweight materials. Then, some of the latest novel strategies to deconstruct condensation polymers to monomers for repolymerization or introduce vulnerable linkers to make the plastics more degradable are discussed. Subsequently, the review will explore the breakthroughs in plastics upcycling by heterogeneous and homogeneous photocatalysis, as well as electrocatalysis, which transform plastics into more versatile fine chemicals and materials while simultaneously mitigating global climate change. In addition, some of the biotechnological advances in the discovery and engineering of microbes that can decompose plastics are also presented. Finally, the current challenges and outlook for future plastics upcycling are discussed to stimulate global cooperation in this field.

Current Developments in the Chemical Upcycling of Waste Plastics Using Alternative Energy Sources.

The management of plastics waste is one of the most urgent and significant global problems now. Historically, waste plastics have been predominantly discarded, mechanically recycled, or incinerated for energy production. However, these approaches typically relied on thermal processes like conventional pyrolysis, which are energy-intensive and unsustainable. In this Minireview, some of the latest advances and future trends in the chemical upcycling of waste plastics by photocatalytic, electrolytic, and microwave-assisted pyrolysis processes are discussed as more environmentally friendly alternatives to conventional thermal reactions. We highlight how the transformation of different types of plastics waste by exploiting alternative energy sources can generate value-added products such as fuels (H2 and other carbon-containing small molecules), chemical feedstocks, and newly functionalized polymers, which can contribute to a more sustainable and circular economy.

Synthesis, properties, and catalysis of p-block complexes supported by bis(arylimino)acenaphthene ligands.

Bis(arylimino)acenaphthene (Ar-BIAN) ligands have been recognized as robust scaffolds for metal complexes since the 1990 s and most of their coordination chemistry was developed with transition metals. Notably, there have been relatively few reports on complexes comprising main group elements, especially those capitalizing on the redox non-innocence of Ar-BIAN ligands supporting p-block elements. Here we present an overview of synthetic approaches to Ar-BIAN ligands and their p-block complexes using conventional solution-based methodologies and environmentally-benign mechanochemical routes. This is followed by a discussion on their catalytic properties, including comparisons to transition metal counterparts, as well as key structural and electronic properties of p-block Ar-BIAN complexes.

A hydrogen-bond facilitated cycle for oxygen reduction by an acid- and base-compatible iron platform.

We report a hydrogen-bond functionalized N4Py ligand platform (N,N-bis(2-R-6-pyridylmethyl)-N-bis(2-pyridyl)methylamine; R = neopentyl-NH, N4Py(2NpNH), 9; R = phenyl-NH, N4Py(2PhNH), 10) and the ability of its iron(II)-triflate [N4Py(2R)Fe(II)(OTf)][OTf] complexes (R = NpNH, 11; R = PhNH, 12) to activate and reduce dioxygen in a synthetic cycle by coupled proton and electron transfer. A pair of iron(III)-hydroxide [N4Py(2R)Fe(III)(OH)][OTf](2) complexes (R = NpNH, 13; R = PhNH, 14) are isolated and structurally and spectroscopically characterized after exposure of the iron(II)-triflate precursors to 1 atm of O(2) at ambient temperature. The stability of this system to acids and bases allows regeneration of the labile iron(II)-triflate starting materials by sequential electron and proton transfer with cobaltocene and triflic acid, respectively, or through direct proton-coupled reduction with ascorbic acid. In the stepwise process, reduction of the iron(III)-hydroxide complexes with cobaltocene gives structurally homologous iron(II)-hydroxide [N4Py(2R)Fe(II)(OH)][OTf] congeners (R = NpNH, 15; R = PhNH, 16) that can be prepared independently from 11 and 12 with 20% aq. NaOH. Additions of triflic acid to complexes 15 and 16 furnish the starting compounds 11 and 12, respectively, to complete the synthetic cycle. The combined data establish a synthetic cycle for O(2) reduction by an iron platform that manages proton and electron transfer through its first and second coordination spheres.

Visible Light-Driven Cascade Carbon-Carbon Bond Scission for Organic Transformations and Plastics Recycling.

Significant efforts are devoted to developing artificial photosynthetic systems to produce fuels and chemicals in order to cope with the exacerbating energy and environmental crises in the world now. Nonetheless, the large-scale reactions that are the focus of the artificial photosynthesis community, such as water splitting, are thus far not economically viable, owing to the existing, cheaper alternatives to the gaseous hydrogen and oxygen products. As a potential substitute for water oxidation, here, a unique, visible light-driven oxygenation of carbon-carbon bonds for the selective transformation of 32 unactivated alcohols, mediated by a vanadium photocatalyst under ambient, atmospheric conditions is presented. Furthermore, since the initial alcohol products remain as substrates, an unprecedented photodriven cascade carbon-carbon bond cleavage of macromolecules can be performed. Accordingly, hydroxyl-terminated polymers such as polyethylene glycol, its block co-polymer with polycaprolactone, and even the non-biodegradable polyethylene can be repurposed into fuels and chemical feedstocks, such as formic acid and methyl formate. Thus, a distinctive approach is presented to integrate the benefits of photoredox catalysis into environmental remediation and artificial photosynthesis.

Completely Solvent-free Protocols to Access Phase-Pure, Metastable Metal Halide Perovskites and Functional Photodetectors from the Precursor Salts.

Mechanochemistry is a green, solid-state, re-emerging synthetic technique that can rapidly form complex molecules and materials without exogenous heat or solvent(s). Herein, we report the application of solvent-free mechanochemical ball milling for the synthesis of metal halide perovskites, to overcome problems with solution-based syntheses. We prepared phase-pure, air-sensitive CsSnX3 (X = I, Br, Cl) and its mixed halide perovskites by mechanochemistry for the first time by reactions between cesium and tin(II) halides. Notably, we report the sole examples where metastable, high-temperature phases like cubic CsSnCl3, cubic CsPbI3, and trigonal FAPbI3 were accessible at ambient temperatures and pressures without post-synthetic processing. The perovskites can be prepared up to "kilogram scales." Lead-free, all-inorganic photodetector devices were fabricated using the mechanosynthesized CsSnBr1.5Cl1.5 under solvent-free conditions and showed 10-fold differences between on-off currents. We highlight an essentially solvent-free, general approach to synthesize metastable compounds and fabricate photodetectors from commercially available precursors.

Artificial photosynthesis by light absorption, charge separation, and multielectron catalysis.

Our society's current energy demands are largely met by the exploitation of fossil fuels, which are unsustainable and environmentally harmful resources. However, Nature has provided us with a clean and virtually limitless alternative in the form of solar energy. This abundant resource is utilized constantly by photosynthetic organisms, which has in turn motivated decades of research in our quest to create artificial counterparts of comparable scales. In this feature article, we will highlight some of the recent novel approaches in the field of artificial photosynthesis (AP), which we define by a more general term as a process that stores energy overall by generating fuels and chemicals using light. We will particularly emphasize on the potential of a highly modular plug-and-play concept that we hope will persuade the community to explore a more inclusive variety of multielectron redox catalysis to complement the proton reduction and water oxidation half-reactions in traditional solar water splitting systems. We discuss some of the latest developments in the vital functions of light harvesting, charge separation, and multielectron reductive and oxidative catalysis, as well as their optimization, to achieve the ultimate goal of storing sunlight in chemical bonds. Specific attention is dedicated to the use of earth-abundant elements and molecular catalysts that offer greater product selectivity and more intricate control over the reactivity than heterogeneous systems. In this context, we showcase our team's contributions in presenting a unique oxidative carbon-carbon bond cleavage reaction in aliphatic alcohols and biomass model compounds, under ambient atmospheric conditions, facilitated by vanadium photocatalysts. We offer this discovery as a promising alternative to water oxidation in an integrated AP system, which would concurrently generate both solar fuels and valuable solar chemicals.