Pascal Vermeeren

Transition metal‐anchored nitrogen‐doped graphene single‐atom catalysts (SACs) have emerged as promising catalysts that combine the advantages of both homogeneous and heterogeneous catalysis. Two common vacancy motifs in nitrogen‐doped graphene‐based SACs are the pyridinic and pyrrolic vacancy sites. Despite their importance for catalyst design, quantitative insights into the intrinsic differences in their metal–support bonding interactions and their impact on the preferred metal binding site are still lacking. Here, we have quantum chemically investigated the trends in bonding interactions between Period 4 transition metals (TM = Ti, V, Cr, Mn, Fe Co, Ni, Cu, and Zn) and these vacancy motifs using relativistic, dispersion‐corrected periodic density functional theory in combination with the activation strain model and Kohn‐Sham molecular orbital (KS‐MO) analyses. Regardless of the vacancy motif, the metal–support interaction follows the same trend across Period 4, namely a strengthening from Ti to Ni followed by a weakening from Ni to Zn. This trend originates from the interplay between the increasing effective nuclear charge and the gradual filling of the metal's 3 d atomic orbitals. Additionally, the vacancy motif plays a key role in determining the preferred transition metal binding site. Ti and V preferentially bind to the larger pyrrolic vacancy site because the planar coordination minimizes Pauli repulsion between the TM and the support. In contrast, Cr through Zn favor the pyridinic motif, where shorter TMN bonds and a larger CNC angle enhance both electrostatic and orbital interactions. Together, these insights could aid in the rational design of future SACs.

We provide design principles for predicting bond exchange kinetics in acylsemicarbazide (ASC)‐based systems that can be applied to tuning the properties of dynamic networks. Because of their capability of dynamic and reversible bond dissociation, ASCs are promising motifs in the design of tunable dynamic covalent networks that combine mechanical robustness with reprocessability and stability. We elucidate the factors that determine the rate of bond dissociation using density functional theory in combination with detailed kinetic studies on the mechanism of the ASC dissociation. Several ASC compounds were investigated, R ¹ ─C(═O)(H)N─N(H)─C(═O)NH─R ² , with R ¹ methyl or phenyl, and R ² methyl, phenyl, or benzoyl, that dissociate into hydrazide and isocyanate parts. The experimentally measured dissociation rate correlates with the proton affinity of the N─H bond next to R ² , which could also be used to predict relative dissociation rates a priori . Proton‐transfer assistance is required for efficient bond exchange. A water molecule, but also neighboring ASCs (reactant) and hydrazides (product), lowers the activation barrier for bond dissociation considerably, likely facilitating autocatalysis that can occur in polymeric ASC networks. These findings can aid in the rational design of reversible polymers based on ASC motifs and can also be generalized for other dynamic covalent networks.

Transition metal-anchored, heteroatom-doped graphene single-atom catalysts have emerged as a promising class of catalysts that combine the strengths of traditional homogeneous and heterogeneous catalysis. Strong metal–support interactions are critical for ensuring long-term catalyst stability and durability. This review assesses strategies for tuning the metal–support interactions in graphene-based single-atom catalysts, with the focus on insights from quantum chemical calculations. By systematically comparing computational studies, we address how variations in key structural and electronic features influence the metal–support bond strength. We evaluate the influence of graphene defect topology by comparing single and double vacancy sites, examine the role of heteroatom dopants (e.g., B, N, or O) in the first coordination sphere, and assess periodic trends by comparing catalytically active transition metals from periods 3, 4, and 5. Overall, this review identifies key structural–electronic features governing metal–support interactions and outlines tuning handles for optimizing metal–support bond strengths.

Catch bonds—dynamic molecular interactions whose lifetimes increase under mechanical load—are central to biological mechanotransduction but remain challenging to replicate synthetically. Here, we report a covalent catch-bonding mechanism in a low-molecular-weight motif based on hydroxyethyl phosphate (HEP) triesters. Our design uses force-mediated inhibition of a neighboring group participation (NGP) pathway: mechanical tension suppresses intramolecular assistance, thereby increasing the reaction barrier and prolonging bond lifetimes. Density Functional Theory calculations confirm that tensile force hinders the geometric contraction required for NGP, providing a mechanistic basis for catch-bond behaviour. Single-molecule force spectroscopy reveals that HEP triester lifetimes increase over threefold at 400 pN. This work establishes a molecular mechanism for engineering covalent catch bonds, offering opportunities to design force-responsive polymer networks. By translating a biological concept into a synthetic framework, our findings open new avenues for adaptive materials and mechanochemical sensing.

Thermosets are made to last. Yet, this very durability creates significant challenges for responsible end-of-life management, rendering conventional recycling nearly impossible. Developing recyclable-by-design thermosets that can be selectively broken down through targeted chemical reactions offers a promising path forward but requires innovative chemistry. While most reported recyclable thermosets are optimized for a single end-of-life route (e.g., chemical depolymerization or reprocessing), achieving multiple distinct circularity pathways in one high-performance thermoset remains challenging. Here, we uncover that hexahydrotriazines─widely used as stable cross-linking units in thermosets─can undergo nucleophilic attack by amines and engage in metathesis reactions, unlocking new avenues for circular material design. Adopting a holistic approach, we first conduct detailed mechanistic studies to elucidate this previously unexplored reactivity, then apply these insights to polyhexahydrotriazine-based thermosets. We demonstrate a single material platform that uniquely combines closed-loop recycling, postsynthetic property reprogramming, repurposing into distinct material architectures, and thermal reprocessing. This multifold circularity introduces a flexible and adaptive strategy for thermoset recycling, addressing the increasing complexity of a circular economy.

The copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction is a foundational transformation in synthetic chemistry, owing to its high efficiency and selectivity. In this work, state‐of‐the‐art quantum chemical methods are applied to elucidate the preference for the dinuclear CuAAC mechanism, involving two copper centers, over the mononuclear analog, involving one copper center. Activation strain and Kohn–Sham molecular orbital analyses reveal that the enhanced reactivity of the dinuclear CuAAC mechanism arises not from alleviation of strain in the copper acetylide upon formation of the six‐membered metallacycle, as previously proposed, but rather from reduced steric Pauli repulsion between the copper acetylide and the azide. These results provide mechanistic insight into the origin of dinuclear catalysis in the CuAAC reaction.

Coordination of chalcogeno-carbonyl ligands CX (X = O, S, Se) to transition metals can induce either expansion (classical) or contraction (nonclassical) of the C-X bond. While nonclassical CO complexes have been extensively studied, the heavier analogs CS and CSe remain comparatively underexplored, despite their higher π-acidity and potential for broader applications. In this work, we used Kohn-Sham molecular orbital theory together with canonical energy decomposition analysis to investigate the nature and bonding characteristics of [M(CO)₅(CX)]^q complexes (M^q = Ti^2-, V^-, Cr⁰, Mn⁺, Fe²⁺). Our results show that nonclassical behavior occurs in the cationic metal complexes, where the trend set by the electrostatic [M]-CX interactions (favoring C-X contraction) dominates the trend set by [M]-CX π-backdonation (favoring C-X expansion), even for the heavier chalcogeno-carbonyl ligands, despite their higher π acidity.

We performed a hierarchical, convergent ab initio benchmark study and systematically analyzed the performance of density functional approximations for describing hydrogen bonds in small neutral, cationic, and anionic complexes, as well as in larger systems involving amide, urea, deltamide, and squaramide moieties. Focal point analyses (FPA), extrapolating to the ab initio limit, were carried out using correlated wave function methods up to CCSDT(Q) for the small complexes and CCSD(T) for the larger systems, together with correlation‐consistent Gaussian basis sets up to the complete basis set limit. Optimized geometries and vibrational frequencies were obtained at the CCSD(T) level. The resulting FPA hydrogen‐bond energies converge within a few tenths of a kcal mol ⁻¹ . These reference data were used to evaluate 60 density functionals (including 12 dispersion‐corrected), spanning the local‐density approximation (LDA), generalized gradient approximations (GGAs), meta‐GGAs, hybrids, meta‐hybrids, double‐hybrids, and range‐separated hybrids. Overall, the meta‐hybrid M06‐2X provides the best performance for both hydrogen bond energies and geometries, while the dispersion‐corrected GGAs BLYP‐D3(BJ) and BLYP‐D4 also yield accurate hydrogen‐bond data and can serve as cost‐effective options for studying large and complex systems.

Transition metal‐anchored nitrogen‐doped graphene single‐atom catalysts (SACs) represent an emerging class of catalysts that combine the advantages of both homogeneous and heterogeneous catalysis. To prevent demetallation and ensure catalyst stability, sufficiently strong bonds between the transition metal and the support are essential. We have quantum chemically analyzed the trend in bonding interaction between period 4 transition metals (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) and the four‐nitrogen‐doped graphene support. We find that the metal–support interactions strengthen from Ti to Ni but weaken from Ni to Zn. Activation strain and Kohn‐Sham molecular orbital (KS‐MO) analyses reveal that this trend stems from changes in the interaction between the metal's 3d_xy atomic orbital and the nitrogen lone pair orbitals of the support. As we move along period 4, the bonding mechanism changes from an increasingly more stabilizing HOMO–LUMO interaction (TM = Ti‐Ni), due to the higher effective nuclear charge of the metal, to a less favorable HOMO–SOMO (TM = Cu) and unfavorable HOMO–HOMO (TM = Zn) interaction, as a result of the filling of the metal's 3d_xy atomic orbital. This results in the observed strengthening, followed by weakening, of the metal–support interaction. These insights could guide the rational design of future single‐atom catalysts.