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1. Coordination-induced O-H/N-H bond weakening by a redox non-innocent, aluminum-containing radical

   https://doi.org/10.1038/s41467-024-45721-1  

   Sinhababu, Soumen; Singh, Roushan Prakash; Radzhabov, Maxim R.; Kumawat, Jugal; Ess, Daniel H.; Mankad, Neal P. (February 2024, Nature Communications)

   Abstract Several renewable energy schemes aim to use the chemical bonds in abundant molecules like water and ammonia as energy reservoirs. Because the O-H and N-H bonds are quite strong (>100 kcal/mol), it is necessary to identify substances that dramatically weaken these bonds to facilitate proton-coupled electron transfer processes required for energy conversion. Usually this is accomplished through coordination-induced bond weakening by redox-active metals. However, coordination-induced bond weakening is difficult with earth’s most abundant metal, aluminum, because of its redox inertness under mild conditions. Here, we report a system that uses aluminum with a redox non-innocent ligand to achieve significant levels of coordination-induced bond weakening of O-H and N-H bonds. The multisite proton-coupled electron transfer manifold described here points to redox non-innocent ligands as a design element to open coordination-induced bond weakening chemistry to more elements in the periodic table. 

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2. Participation of S and Se in hydrogen and chalcogen bonds

   https://doi.org/10.1039/D1CE01046H  

   Scheiner, Steve (October 2021, CrystEngComm)

   This article reviews the history and the current state of knowledge concerning the ability of the heavy chalcogen atoms S and Se, and to some extent Te, to participate in a H-bond as either proton donor or acceptor. These atoms are nearly as effective proton acceptors as O, and only slightly weaker as donor. They can also participate in chalcogen bonds where they act as electron acceptors from a nucleophile. These bonds rapidly strengthen as the chalcogen atom becomes larger: S < Se < Te, or if they are surrounded by electron-withdrawing substituents, and can exceed that of many types of H-bonds. Experimental and computational evidence indicates that both H-bonds and chalcogen bonds involving S and Se occur widely in chemical and biological systems, and play an active role in structure and function. 

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3. A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main‐Group‐Element Catalysis

   https://doi.org/10.1002/anie.202206325  

   Chaturvedi, Ashwin; McCarver, Gavin A.; Sinha, Soumalya; Hix, Elijah G.; Vogiatzis, Konstantinos D.; Jiang, Jianbing (July 2022, Angewandte Chemie International Edition)

   Abstract Electrocatalytic proton reduction to form dihydrogen (H₂) is an effective way to store energy in the form of chemical bonds. In this study, we validate the applicability of a main‐group‐element‐based tin porphyrin complex as an effective molecular electrocatalyst for proton reduction. A PEGylated Sn porphyrin complex (SnPEGP) displayed high activity (−4.6 mA cm⁻²at −1.7 V vs. Fc/Fc⁺) and high selectivity (H₂Faradaic efficiency of 94 % at −1.7 V vs. Fc/Fc⁺) in acetonitrile (MeCN) with trifluoroacetic acid (TFA) as the proton source. The maximum turnover frequency (TOF_max) for H₂production was obtained as 1099 s⁻¹. Spectroelectrochemical analysis, in conjunction with quantum chemical calculations, suggest that proton reduction occurs via an electron‐chemical‐electron‐chemical (ECEC) pathway. This study reveals that the tin porphyrin catalyst serves as a novel platform for investigating molecular electrocatalytic reactions and provides new mechanistic insights into proton reduction. 

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4. CdS Quantum Dot Gels as a Direct Hydrogen Atom Transfer Photocatalyst for C−H Activation

   https://doi.org/10.1002/anie.202403186  

   Liu, Daohua; Hazra, Atanu; Liu, Xiaolong; Maity, Rajendra; Tan, Ting; Luo, Long (August 2024, Angewandte Chemie International Edition)

   Abstract Here, we report CdS quantum dot (QD) gels, a three‐dimensional network of interconnected CdS QDs, as a new type of direct hydrogen atom transfer (d‐HAT) photocatalyst for C−H activation. We discovered that the photoexcited CdS QD gel could generate various neutral radicals, including α‐amido, heterocyclic, acyl, and benzylic radicals, from their corresponding stable molecular substrates, including amides, thio/ethers, aldehydes, and benzylic compounds. Its C−H activation ability imparts a broad substrate and reaction scope. The mechanistic study reveals that this reactivity is intrinsic to CdS materials, and the neutral radical generation did not proceed via the conventional sequential electron transfer and proton transfer pathway. Instead, the C−H bonds are activated by the photoexcited CdS QD gel via a d‐HAT mechanism. This d‐HAT mechanism is supported by the linear correlation between the logarithm of the C−H bond activation rate constant and the C−H bond dissociation energy (BDE) with a Brønsted slopeα=0.5. Our findings expand the currently limited direct hydrogen atom transfer photocatalysis toolbox and provide new possibilities for photocatalytic C−H activation. 

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5. Facile proton-coupled electron transfer enabled by coordination-induced E–H bond weakening to boron

   https://doi.org/10.1039/D1CC02832D  

   Wong, Anthony; Chakraborty, Arunavo; Bawari, Deependra; Wu, Guang; Dobrovetsky, Roman; Ménard, Gabriel (January 2021, Chemical Communications)

   null (Ed.)

   We report the facile activation of aryl E–H (ArEH; E = N, O, S; Ar = Ph or C 6 F 5 ) or ammonia N–H bonds via coordination-induced bond weakening to a redox-active boron center in the complex, (1 − ). Substantial decreases in E–H bond dissociation free energies (BDFEs) are observed upon substrate coordination, enabling subsequent facile proton-coupled electron transfer (PCET). A drop of >50 kcal mol −1 in H 2 N–H BDFE upon coordination was experimentally determined. 

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