Eveline H. Tiekink

The binding affinities for a series of Lewis acids (LAs) to acrolein and azabutadiene were investigated using density functional theory calculations at ZORA-BLYP-D3(BJ)/TZ2P. In all systems, LAs favor σ-binding to the lone pair of nitrogen or oxygen, rather than π-binding to the C=C double bond. Activation strain and energy decomposition analyses reveal that σ-binding is preferred over π-binding due to reduced steric (Pauli) repulsion between the LA and the substrate. Furthermore, LAs σ-bind more strongly to the nitrogen of azabutadiene than to the oxygen of acrolein due to enhanced electrostatic and orbital interactions. In addition, the role of solvation in the σ-binding versus π-binding preference was also examined: the preference for σ-binding clearly remains and even increases for strong LAs, but for weak LAs such as I2, the preference for σ-binding diminishes in solvent, though σ-binding remains dominant. Lastly, analysis of I2 catalysis of a model Diels-Alder reaction indicates that the preferred transition state features σ-binding. Overall, π-binding appears to be more of a (theoretical) curiosity and is unlikely to play a dominant role in catalysis.

The enantioselective construction of small ring carbocycles provides organic chemists with an enduring challenge.¹ Despite their commercial importance, enantioselective synthetic routes towards alkylidenecyclopropanes (ACPs), a class of small ring carbocycles, remain underdeveloped.^2,3 Importantly, ACPs can be converted into cyclopropanes, a common feature in drug molecules (e.g. Nirmatrelvir, 1),⁴ as well as both naturally occurring and synthetic agrochemicals (e.q. permethrin 2).^5,6 We now describe the facile synthesis of highly enantioenriched alkylidenecyclopropanes through the use of a bifunctional iminophosphorane (BIMP) catalysed, stereo-controlled, strain-relieving deconjugation. Small modifications to the basic catalyst system were used to broaden the scope of the reaction to substrates containing ester, amide, phosphine oxide, and ketone functionalities. Through the design of a suitable substrate and re-tuning of the catalyst's iminophosphorane moiety, the transformation was effectively applied to the synthesis of a single stereoisomer of the commonplace insecticide permethrin as well as a range of cyclopropane-based insecticide cores. State-of-the-art computational studies were performed to provide detailed insight into the mechanistic pathway and origin of both diastereo- and enantioselectivities.

The activation of small molecules is a crucial step in advancing sustainable chemistry, enabling key transformations in fine chemical synthesis and energy storage. While transition metals have traditionally dominated this field, main‐group elements—specifically metallylenes, which are heavier analogs of carbenes (silylenes, germylenes, stannylenes, and plumbylenes)—have emerged as viable alternatives due to their unique electronic properties and tunable reactivity. This review explores the mechanisms by which metallylenes activate small molecules, highlighting the influence of ligand design, electronic structure, and geometric factors. We discuss recent advances in the field, including computational insights into metallylene‐mediated bond activation and experimental demonstrations of their catalytic potential. Additionally, we examine follow‐up reactions such as hydrogenation and hydroboration, which illustrate the versatility of metallylenes in small‐molecule transformation. By providing a comprehensive overview of the latest developments, this review aims to bridge fundamental principles with potential applications, paving the way for metallylene‐based catalysis in sustainable chemistry.

The activation of small molecules is a crucial step in advancing sustainable chemistry, enabling key transformations in fine chemical synthesis and energy storage. While transition metals have traditionally dominated this field, main-group elements—specifically metallylenes, which are heavier analogs of carbenes (silylenes, germylenes, stannylenes, and plumbylenes)—have emerged as viable alternatives due to their unique electronic properties and tunable reactivity. This review explores the mechanisms by which metallylenes activate small molecules, highlighting the influence of ligand design, electronic structure, and geometric factors. We discuss recent advances in the field, including computational insights into metallylene-mediated bond activation and experimental demonstrations of their catalytic potential. Additionally, we examine follow-up reactions such as hydrogenation and hydroboration, which illustrate the versatility of metallylenes in small-molecule transformation. By providing a comprehensive overview of the latest developments, this review aims to bridge fundamental principles with potential applications, paving the way for metallylene-based catalysis in sustainable chemistry.

We have quantum chemically investigated the catalytic effect of hydrogen bonding organocatalysts, (H ₂ N) ₂ C=X (X=O, S, Se, NH, PH, AsH, CH ₂ , SiH ₂ GeH ₂ ), such as urea, on the classic Diels‐Alder reaction. All studied hydrogen bond donor catalysts enhance the Diels‐Alder reaction between acrolein and 1,3‐butadiene to a similar extent. Our activation strain and Kohn‐Sham molecular orbital analyses show that these organocatalysts lower the reaction barrier by polarizing the π‐orbitals away from the reactive carbon atoms of acrolein, reducing the Pauli repulsion between the reactants. Interestingly, this catalytic mechanism is not limited to >C=X moieties with relatively electronegative X (e. g., O, S, NH) but extends to situations like >C=CH ₂ and even >C=SiH ₂ .

The homologous series of gaseous C1-4 alkanes represents one of the most abundant sources of short alkyl fragments. However, their application in synthetic organic chemistry is exceedingly rare due to the challenging C–H bond cleavage, which typically demands high temperatures and pressures, thereby limiting their utility in the construction of complex organic molecules. In particular, the formation of C(sp2)–C(sp3) bonds is crucial for constructing biologically active molecules, including pharmaceuticals and agrochemicals. In this study, we present the previously elusive coupling between gaseous alkanes and (hetero)aryl bromides, achieved through a combination of Hydrogen Atom Transfer (HAT) photocatalysis and nickel-catalyzed cross coupling at room temperature. Utilizing flow technology allowed us to conduct this novel coupling reaction with reduced reaction times and in a scalable fashion, rendering it practical for widespread adoption in both academia and industry. Density Functional Theory (DFT) calculations unveiled that the oxidative addition constitutes the rate-determining step, with the activation energy barrier increasing with smaller alkyl radicals. Furthermore, radical isomerization observed in propane and butane analogues could be attributed to the electronic properties of the bromoarene coupling partner, highlighting the crucial role of oxidative addition in the observed selectivity of this transformation.

Correction for ‘Not antiaromaticity gain, but increased asynchronicity enhances the Diels–Alder reactivity of tropone’ by Eveline H. Tiekink et al., Chem. Commun., 2023, 59, 3703–3706, https://doi.org/10.1039/D3CC00512G.