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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. (December 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. Adjustment of the Proton‐Accepting Ability of Π‐Bonds and Lone Pairs

   https://doi.org/10.1002/cphc.202500448  

   Amonov, Akhtam; Scheiner, Steve (October 2025, ChemPhysChem)

   A hydroxyl group is placed on a series of systems containing CC double bonds, and quantum chemical calculations consider the preferred target of an incoming1 HCl molecule to form an H‐bond. The O lone pairs are favored over the π‐system in most instances but can be reversed by the presence of electron‐donating substituents. This reversal occurs when NH₂groups are added to a simple alkene or if NMe₂substituents are placed on a conjugated butadiene derivative. There are a variety of means of favoring the aromatic ring as a proton‐accepting site over the phenol O. Dispersion is the primary factor in determining the preferred electron‐donor site in the aromatic systems. The particular site and orientation of attachment of HCl to theπsystem is controlled by a combination of electrostatic potential and HOMO disposition. 

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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/ange.202403186  

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

   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. Site- and stereoselective silver-catalyzed intramolecular amination of electron-deficient heterobenzylic C–H bonds

   https://doi.org/10.1039/D4SC08757G  

   Trinh, Tuan Anh; Cherempei, Stanislav; Rampon, Daniel S; Schomaker, Jennifer M (January 2025, Chemical Science)

   Rational ligand design in a silver catalyst enables highly selective amination of electron-deficient heterobenzylic C–H bondsvianitrene transfer, with scaffold rigidity crucial for unlocking this elusive reactivity in heteroaromatic compounds. 

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