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The synthesis of housane derivatives from cyclopropenes is described. Under rhodium(II) catalysis, cyclopropenylvinyl carbinols can regioselectively generate a carbene intermediate which undergoes an intramolecular cyclopropanation to form a housane, a skeleton with similar ring strain as the cyclopropene precursor. The procedure shows a remarkable broad scope and efficiency. Moreover, the method served to prepare man-made housane-containing terpene derivatives, which are not accessible by Nature., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A computational approach to directly estimate the relative acidity of a given Lewis acid is presented. This approach is based on the strength of the π-conjugation in trans-crotonaldehyde-Lewis acid complexes, the species used in the well-known Childs' Lewis acidity scale. It is found that the π-conjugative strength values given by the Energy Decomposition Analysis - Natural Orbital for Chemical Valence method strongly correlate not only with the variation of the bond lengths in the system, which are greatly affected by the nature of the Lewis acid, but also with the downfield shifts experienced by the different nuclei of the conjugated system upon binding to the Lewis acid. These strong correlations indicate that the (easy-to-compute) π-conjugation energies can be used as an alternative Lewis acidity scale., (© 2024 The Author(s). Chemistry - An Asian Journal published by Wiley-VCH GmbH.)

Organic dyes are interesting building blocks for the preparation of organic semiconductors as they possess synthetic handles that can be used to functionalize them and, consequently, change their electronic properties. However, reactions to extend their π-conjugated framework through ring annulation have only been scarcely tested. Herein, we report the use of alkyne benzannulation on 2,8-dibromo-dibenzo[def,mno]chrysene (vat orange 3) and 2,9-dibromo-dibenzo[b,def]chrysene (vat orange 1) to extend the conjugation and reduce their bandgap. Unexpectedly, the ring closure reaction takes place at the most sterically hindered positions (peri to the substituent) to yield contorted polycyclic compounds. More surprisingly, both TIPS-acetylene-functionalized derivatives underwent a tandem dearomative spirocyclization to form bent polycyclic compounds. Absorption spectroscopy reveals that ring annulation on both 2,9-dibromo-dibenzo[b,def]chrysene and 2,8-dibromo-dibenzo[def,mno]chrysene resulted in a decrease of 0.38 and 0.12 eV in bandgap values, respectively, despite inducing a contorted conformation., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

A visible-light-induced intramolecular diradical-mediated hydrogen atom transfer (DHAT) of primary, secondary, and tertiary C(sp 3 )-H bonds and subsequent cyclization is described. This transformation is enabled by triplet energy transfer upon Lewis acid coordination to alkyl-substituted arylvinylpyridines and gives access to a variety of benzocyclobutenes (>40 examples, 32-96% yield). Notably, tri- and tetrasubstituted olefins with tertiary C(sp 3 )-H bonds effectively delivered sterically hindered products with adjacent all-carbon quaternary centers. Mechanistic evidence and density functional theory (DFT) calculations suggest that Lewis acid coordination was crucial for the success by modulating the reactivity of the diradical intermediates to unlock a challenging carbon-to-carbon DHAT and subsequent cyclization with a rather low barrier, which allows the functionalization of benzylic C(sp 3 )-H bonds to construct otherwise inaccessible benzocyclobutenes.

Conventional genome editing tools rely on DNA double-strand breaks (DSBs) and host recombination proteins to achieve large insertions, resulting in a heterogeneous mixture of undesirable editing outcomes. We recently leveraged a type I-F CRISPR-associated transposase (CAST) from the Pseudoalteromonas Tn 7016 transposon ( Pse CAST) for DSB-free, RNA-guided DNA integration in human cells, taking advantage of its programmability and large payload capacity. Pse CAST is the only characterized CAST system that has achieved human genomic DNA insertions, but multiple lines of evidence suggest that DNA binding may be a critical bottleneck that limits high-efficiency activity. Here we report structural determinants of target DNA recognition by the Pse CAST QCascade complex using single-particle cryogenic electron microscopy (cryoEM), which revealed novel subtype-specific interactions and RNA-DNA heteroduplex features. By combining our structural data with target DNA library screens and rationally engineered protein mutations, we uncovered CAST variants that exhibit increased integration efficiency and modified PAM stringency. Structure predictions of key interfaces in the transpososome holoenzyme also revealed opportunities for the design of hybrid CASTs, which we leveraged to build chimeric systems that combine high-activity DNA binding and DNA integration modules. Collectively, our work provides unique structural insights into type I-F CAST systems while showcasing multiple diverse strategies to investigate and engineer new RNA-guided transposase architectures for human genome editing applications.

The synthesis of diradical organic compounds has garnered significant attention due to their thermally accessible spin inversion and optoelectronic properties. Yet, preparing such stable structures with high open-shell behavior remains challenging. Herein, we report the synthesis and properties of four π-extended, fused fluorene derivatives with high diradical character, taking advantage of a molecular design where the closed-shell does not include any Clar sextet, comparatively to a maximum of 5 in the corresponding open-shell state. This led to an unusual open-shell triplet ground state with an outstanding singlet-triplet energy difference (ΔE ST ) of ca. 19 kcal/mol, one of the highest values reported to date for an all-carbon conjugated scaffold. Incorporation of dithiafulvene units at each end of the molecule (at the five-membered rings) furnishes extended tetrathiafulvalenes (TTFs) undergoing reversible oxidations to the radical cation and diradical dication. The various pro-aromatic structures presented herein show highly localized spin density and a limited conjugation due to the confined π-electrons in the aromatic cycles, as supported by 1 H NMR, UV/Visible, EPR spectroscopy and DFT calculations., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A bare lead atom is a σ-donor ligand capable of linearly bonding and stabilizing two units of a classical polyhydride complex, with a high-valent metal center. As a proof of concept, we have prepared and characterized the μ 2 -tetrylide complex (P i Pr 3 ) 2 H 4 Os═Pb═OsH 4 (P i Pr 3 ) 2 in the reaction of OsH 6 (P i Pr 3 ) 2 with Pb{N(SiMe 3 ) 2 } 2 . Although the Pb-Os bonds exhibit electrostatic interaction, the main orbital interactions result from two dative σ bonds from the lead atom to the osmium centers. The latter also provide much weaker π-backdonations.

New and simple ligand design strategies for the preparation of versatile metal-based catalysts capable of operating under greener and eco-friendly conditions in several industrially attractive processes are in high demand for society development. We present the first nucleophilic addition of an organolithium to ketenimines which incorporates a stereogenic centre in an N-donor atom to prepare new enantiopure NNN-donor scorpionates. We have also verified its potential utility as a valuable scaffold for chirality induction through the preparation of inexpensive, non-toxic and asymmetric zinc complexes. The pro-ligands and the corresponding zinc-based complexes have been characterized by X-ray diffraction studies. DFT studies were carried out to rationalize the different complexation abilities of these pro-ligands. These complexes have proved to act as highly efficient catalysts for a variety of sustainable bioresourced processes that are industrially attractive, with a wide substrate scope. Thus, complex 7 behaves as a highly efficient initiator for the well-behaved living ring-opening polymerization (ROP) of rac -lactide under very mild conditions. The PLA materials produced exhibited enhanced levels of isoselectivity, comparable to the highest value reported so far for zinc-based catalysts ( P i = 0.88). In addition, the combination of 7 with onium halide salts functioned as a very active and selective catalyst for CO 2 fixation into five-membered cyclic carbonates through the cycloaddition of CO 2 into epoxides under very mild and solvent-free conditions, reaching very good to excellent conversions (TOF = 227 h -1 ). Furthermore, this bicomponent system exhibits a broad substrate scope and functional group tolerance, including mono- and di-substituted epoxides, as well as the very challenging bio-renewable tri-substituted terpene-derived cis / trans -limonene oxide, whose reaction proceeds with high stereoselectivity. Finally, complex 7 also achieved high activity and selectivity as a one-component initiator for the synthesis of poly(cyclohexene carbonate)s via ring-opening copolymerization (ROCOP) of cyclohexene oxide and CO 2 under very soft conditions, affording materials with narrow dispersity values.

While metal-ligand cooperativity is well-known, studies on element-ligand cooperativity involving main group species are comparatively much less explored. In this study, we computationally designed a few geometrically constrained borylenes supported by different carbenes. Our density functional theory studies indicate that they possess enhanced nucleophilicity as well as electrophilicity, thus rendering them promising candidates for exhibiting borylene-ligand cooperativity. The cooperation between the boron and adjacent carbene centers facilitates different bond activation processes, including the cycloaddition of acetylene across the boron-carbene bond as well as B-H/Si-H bond activation reactions, which have been analyzed in detail. To the best of our knowledge, the borylenes proposed in this study represent the first examples of theoretically proposed geometrically constrained bis(carbene)-stabilized borylenes capable of cooperative activation of enthalpically strong bonds.

Low-valent cobalt complexes can promote intramolecular (3 + 2) cycloadditions of alkyne-tethered cyclopropenes to provide bicyclic systems containing highly substituted cyclopentadienyl moieties with electronically diverse functional groups. The adducts can be easily transformed into new types of CpRh(III) and CpIr(III) complexes, which show catalytic activity in several relevant transformations. Preliminary computational (DFT) and experimental studies provide relevant information on the mechanistic peculiarities of the cobalt-catalyzed process and allow us to rationalize its advantages over the homologous rhodium-promoted reaction., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Quantum chemical calculations were carried out to quantitatively understand the origin of the Felkin-Anh(-Eisenstein) model, widely used to rationalize the π-facial stereoselectivity in the nucleophilic addition reaction to carbonyl groups directly attached to a stereogenic center. To this end, the possible approaches of cyanide to both ( S )-2-phenylpropanal and ( S )-3-phenylbutan-2-one have been explored in detail. With the help of the activation strain model of reactivity and the energy decomposition analysis method, it is found that the preference for the Felkin-Anh addition is mainly dictated by steric factors which manifest in a less destabilizing strain-energy rather than, as traditionally considered, in a lower Pauli repulsion. In addition, other factors such as the more favorable electrostatic interactions also contribute to the preferred approach of the nucleophile. Our work, therefore, provides a different, more complete rationalization, based on quantitative analyses, of the origin of this seminal and highly useful concept in organic chemistry., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Directional bonding strategies guide the design of complex molecular architectures, yet challenges arise due to emergent behavior. Rigid structures face geometric constraints and sensitivity to mismatches, hindering the efficient assembly of molecular organic cages (MOCs). Harnessing intramolecular non-covalent interactions offers a promising solution, broadening geometrical possibilities and enhancing adaptability to boost assembly yields. However, identifying these interactions remains challenging, with their full potential sometimes latent until final assembly. This study explores these challenges by synthesizing boronic acid tripods with varied oxygen positions at the tripodal feet and investigating their role in assembling tetrahedral boronate MOCs. Our results reveal substantial differences in the assembly efficiency among tripods. While the building blocks with oxygen in the benzylic position relative to the central aromatic ring form the MOCs in high yields, those with the oxygen atom directly bound to the central aromatic ring, only yield traces. Through X-ray crystallography and DFT analyses, we elucidate how intramolecular interactions profoundly influence the geometry of the building blocks and cages in a relay-like fashion, highlighting the importance of considering intramolecular interactions in the rational design of (supra)molecular architectures., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The synthesis, structure, and catalytic activity of a Ti(II)/Ti(III) inverted sandwich compound are presented in this study. Synthesis of the arene-bridged dititanium compound begins with the preparation of the titanium(IV) precursor [TiCl 2 ( Mes PDA)(thf) 2 ] ( Mes PDA = N , N '-bis(2,4,6-trimethylphenyl)- o -phenylenediamide) ( 2 ). The reduction of 2 with sodium metal results in species [{Ti( Mes PDA)(thf)} 2 (μ-Cl) 3 {Na}] ( 3 ) in oxidation state III. To achieve the lower oxidation state II, 2 undergoes reduction through alkylation with lithium cyclopentyl. This alkylation approach triggers a cascade of reactions, including β-hydride abstraction/elimination, hydrogen evolution, and chemical reduction, to generate the Ti(II)/Ti(III) compound [Li(thf) 4 ][(Ti Mes PDA) 2 (μ-η 6 : η 6 -C 6 H 6 )] ( 4 ). X-ray and EPR characterization confirms the mixed-valence states of the titanium species. Compound 4 catalyzes a mild, efficient, and regiospecific cyclotrimerization of alkynes to form 1,3,5-substituted arenes. Kinetic data support a mechanism involving a binuclear titanium arene compound, similar to compound 4 , as the resting state. The active catalyst promotes the oxidative coupling of two alkynes in the rate-limiting step, followed by a rapid [4 + 2] cycloaddition to form the arene product. Computational analysis of the resting state for the cycloaddition of trimethylsilylacetylene indicates a thermodynamic preference for stabilizing the 1,3,5-arene within the space between the two [Ti Mes PDA] fragments, consistent with the observed regioselectivity.

Conjugated dienes (1,3-dienes) are versatile and valuable chemical feedstocks that can be used as two-carbon or four-carbon synthons with vast applications across the chemical industry. However, the main challenge for their productive incorporation in synthetic routes is their chemo-, regio-, and stereoselective functionalization. Herein, we introduce a unified strategy for the 1,2-hydroarylation and 1,4-trifluoromethylarylation of 1,3-dienes using anilines in hexafluoroisopropanol. DFT calculations point toward a kinetically controlled process in both transformations, particularly in the trifluoromethylarylation, to explain the regiodivergent outcome. In addition, we perform an extensive program of functionalization and diversification of the products obtained, including hydrogenation, oxidation, cyclizations, or cross-coupling reactions, that allows access to a library of high-value species in a straightforward manner., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

We report on the synthesis and characterization of a series of (mostly) air-stable diorganyl bis(pyridylimino) isoindolide (BPI) aluminum complexes and their chemistry upon visible-light excitation. The redox non-innocent BPI pincer ligand allows for efficient charge transfer homolytic processes of the title compounds. This makes them a universal platform for the generation of carbon-centered radicals. The photo-induced homolytic cleavage of the Al-C bonds was investigated by means of stationary and transient UV/Vis spectroscopy, spin trapping experiments, as well as EPR and NMR spectroscopy. The experimental findings were supported by quantum chemical calculations. Reactivity studies enabled the utilization of the aluminum complexes as reactants in tin-free Giese-type reactions and carbonyl alkylations under ambient conditions, which both indicated radical-polar crossover behavior. A deeper understanding of the physical fundamentals and photochemical process was provided, furnishing in turn a new strategy to control the reactivity of bench-stable aluminum organometallics., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Catalysts generated in situ by the combination of pyridine-hydrazone N , N -ligands and Pd(TFA) 2 have been applied to the addition of arylboronic acids to formylphosphonate-derived hydrazones, yielding α-aryl α-hydrazino phosphonates in excellent enantioselectivities (96 → 99% ee). Subsequent removal of the benzyloxycarbonyl (Cbz) N -protecting group afforded key building blocks en route to appealing artificial peptides, herbicides and antitumoral derivatives. Experimental and computational data support a stereochemical model based on aryl-palladium intermediates in which the phosphono hydrazone coordinates in its Z -configuration, maximizing the interactions between the substrate and the pyridine-hydrazone ligand., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

An unexpected Lewis acid-catalyzed carbohydrate rearrangement of a 1,5-bis-glycopyranoside to the product of a formal intramolecular C -aryl glycosylation reaction is reported. Mechanistic studies based mainly on intermediate trapping experiments and density functional theory (DFT) calculations reveal a cascade process involving three transient (a)cyclic oxocarbenium cations, the breaking of three single C(sp 3 )-O bonds, and the formation of three single bonds (i.e., exo -, endo -, and C -glycosidic bonds), leading to the 2,6-epoxybenzoxocine skeleton of bioactive natural glycoconjugates related to serjanione A and mimocaesalpin E. DFT calculations established that the generation of the pyran moiety embedded in the bridged benzoxocin ring system is likely to proceed through an unusual ring-closure of an ortho-quinone methide intermediate in which the attacking nucleophile is a carbonyl oxygen.

The factors governing the acceleration of the oxidative addition of methyl iodide to pincer rhodium(I)-complexes induced by coronene have been computationally explored in detail using quantum chemical methods. Both the parent reaction and the coronene-mediated process proceed via a stepwise S N 2-type mechanism. It is found that the acceleration of the process derives from the formation of an initial supramolecular complex, mainly stabilized by electrostatic and π-π interactions, which significantly increases the electron richness of the complex. The impact of this effect on the reaction barrier has been quantitatively analyzed by applying the activation strain model in combination with the energy decomposition analysis method. In addition, the influence of other polycyclic aromatic hydrocarbons on the oxidative reaction has been also considered., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

The factors governing 1,3-dipolar cycloaddition reactions involving C≡P-containing compounds are computationally explored in detail using quantum chemical tools. To this end, the parent process involving tBuN 3 and tBuCP is analyzed and compared to the analogous reaction involving organometallic cyaphide complexes (metal=Au, Pt, Ge, Mg), in order to understand the role of the metal fragment in such transformations. It is found that while the metal fragment does not significantly influence the aromaticity of the corresponding concerted transition states or the regioselectivity of the transformation, it may modify the reactivity of the cyaphide complexes (i. e. Ge and Mg cyaphide complexes are comparatively more reactive). The computed reactivity trends and the factors behind the regioselectivity of the cycloaddition reaction are quantitatively analyzed with the help of the activation strain model in combination with the energy decomposition analysis method., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

A straightforward and selective conversion of nitriles into highly substituted tetrahydropyridines, aminoketones or enamines by using allylmagnesium bromide as an addition partner (under neat conditions) and subsequent treatment with different aqueous-based hydrolysis protocols is reported. Refuting the conventional wisdom of the incompatibility of Grignard reagents with air and moisture, we herein report that the presence of water allows us to promote the chemoselective formation of the target tetrahydropyridines over other competing products (even in the case of highly challenging aliphatic nitriles). Moreover, the careful tuning of both the reaction media employed (acid or basic aqueous solutions for the hydrolysis protocol) and the electronic properties of the starting nitriles allowed us to design a multi-task system capable of producing either β-aminoketones or enamines in a totally selective manner. Importantly, and for the first time in the chemistry of main-group polar organometallic reagents in non-conventional protic solvents ( e.g. , water), both experimental and computational studies showed that the excellent efficiency and selectivity observed in aqueous media cannot be replicated by using standard dry volatile organic solvents (VOCs) under inert atmosphere conditions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Quantum-chemical (DFT) calculations on hitherto unknown base(carbene)-stabilized gallium monoiodides (LB→GaI) suggest that these systems feature one lone pair of electrons and a formally vacant p-orbital - both centered at the central gallium atom - and exhibit metallomimetic behavior. The calculated reaction free energies as well as bond dissociation energies suggest that these LB→GaI systems are capable of forming stable donor-acceptor complexes with group 13 trichlorides. Examination of the ligand exchange reactions with iron and nickel complexes indicates their potential use as ligands in transition metal chemistry. In addition, it is found that the title compounds are also able to activate various enthalpically robust bonds. Further, a detailed mechanistic investigation of these small molecule activation processes reveals the non-innocent behavior of the carbene (base) moiety attached to the GaI fragment, thereby indicating the cooperative nature of these bond activation processes. The energy decomposition analysis (EDA) and activation strain model (ASM) of reactivity were also employed to quantitatively understand and rationalize the different activation processes., (© 2023 Wiley-VCH GmbH.)

Herein, we present that the radicals [Ph 3 PC(Me)EMes 2 ]˙ (2Si and 2Ge) can be generated from the α-silylated and α-germylated phosphorus ylides Ph 3 PC(Me)E(Cl)Mes 2 (1Si and 1Ge) through one-electron reduction with Jones' dimer ( Mes NacNacMg) 2 in benzene. Although isolation of the free radicals was not possible, the products of the intramolecular addition of the radicals to a phenyl substituent of the phosphorus moiety, followed by subsequent reaction with 2Si or 2Ge to the isolated species 3Si and 3Ge, respectively, were observed. This transformation witnesses a dearomative 1,4-addition of tetryl radical species to the phenyl scaffold in a stereoselective anti -fashion.

Herein, we report the use of isonitriles as alkyl radical precursors in light-mediated hydro- and deuterodeamination reactions. The reaction is scalable, shows broad functional group compatibility and potential to be used in late-stage functionalization. Importantly, the method is general for C α -primary, C α -secondary and C α -tertiary alkyl isonitriles. For most examples, high yields were obtained through direct visible-light irradiation of the isonitrile in the presence of a silyl radical precursor. Interestingly, in the presence of an organic photocatalyst (4CzIPN) a dramatic acceleration was observed. In-depth mechanistic studies using UV/Vis absorption, steady-state and time-resolved photoluminescence, and transient absorption spectroscopy suggest that the excited state of 4CzIPN can engage in a single-electron transfer with the isonitrile., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The origin of the electrophilicity of a series of cyclohexanones and benzaldehydes is investigated using the activation strain model and quantitative Kohn-Sham molecular orbital (MO) theory. We find that this electrophilicity is mainly determined by the electrostatic attractions between the carbonyl compound and the nucleophile (cyanide) along the entire reaction coordinate. Donor-acceptor frontier molecular orbital interactions, on which the current rationale behind electrophilicity trends is based, appear to have little or no significant influence on the reactivity of these carbonyl compounds., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We report on so-called "hidden FLPs" (FLP: frustrated Lewis pair) consisting of a phosphorus ylide featuring a group 13 fragment in the ortho position of a phenyl ring scaffold to form five-membered ring structures. Although the formation of the Lewis acid/base adducts was observed in the solid state, most of the title compounds readily react with carbon dioxide to provide stable insertion products. Strikingly, 0.3-3.0 mol% of the reported aluminum and gallium/carbon-based ambiphiles catalyze the reduction of CO 2 to methanol with satisfactory high selectivity and yields using pinacol borane as stoichiometric reduction equivalent. Comprehensive computational studies provided valuable mechanistic insights and shed more light on activity differences., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Despite recent achievements in the field of frustrated Lewis pairs (FLPs) for small molecule activations, the reversible activation and catalytic transformations of N-H-activated ammonia remain a challenge. Here we report on a rare combination of an aluminium Lewis acid and a carbon Lewis base. A so-called hidden FLP consisting of a phosphorus ylide featuring an aluminium fragment in the ortho position of a phenyl ring scaffold is introduced. Although the formation of the Lewis acid/base adduct is observed in the solid state, which at first glance leads to formally quenched FLP reactivity, we show that the title compound readily reacts with non-aqueous ammonia thermoneutrally and splits the N-H bond reversibly at ambient temperature. In addition, NH 3 transfer reactions mediated by a main-group catalyst are presented. This proof-of-principle study is expected to initiate further activities in utilizing N-H-activated ammonia as a readily available, atom-economical nitrogen source., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Cobalt(I) catalysts equipped with bisphosphine ligands can be used to promote formal (3 + 2 + 2) intramolecular cycloadditions of enynylidenecyclopropanes of type 1 . The method provides synthetically appealing 5,7,5-fused tricyclic systems in good yields and with complete diastereo- and chemoselectivity. Interestingly, its scope differs from that of previously reported annulations based on precious metal catalysts, specifically rhodium and palladium. Noticeably, density functional theory calculations confirm that the mechanism of the reaction is also different from those proposed for these other catalysts.

The mechanism and selectivity patterns of the DABCO-catalyzed Cloke-Wilson rearrangement were computationally studied in detail using density functional theory calculations. Our computations suggest that the process occurs stepwise involving the initial ring opening of the cyclopropane promoted by a DABCO molecule followed by a ring-closure reaction of the readily formed zwitterionic intermediate. The regioselectivity of the initial nucleophilic ring-opening step strongly depends on the nature of the substituent attached to the cyclopropane moiety. The physical factors governing the preference for the more sterically hindered C2 (tertiary) position have been quantitatively analyzed by applying the combined activation strain model-energy decomposition analysis method. In addition, our calculations revealed a new mechanism for the analogous transformation involving vinylcyclopropanes consisting of an initial S N 2' ring-opening process followed by a 5-exo-trig cyclization step, which proceeds without facial selectivity.

Understanding the geometrical preferences in chemical reactions is crucial for advancing the field of organic chemistry and improving synthetic strategies. One such preference, the Bürgi-Dunitz angle, is central to nucleophilic addition reactions involving carbonyl groups. This study successfully employs a novel two-dimensional Distortion-Interaction/Activation-Strain Model in combination with a two-dimensional Energy Decomposition Analysis to investigate the origins of the Bürgi-Dunitz angle in the addition reaction of CN - to (CH 3 ) 2 C═O. We constructed a 2D potential energy surface defined by the distance between the nucleophile and carbonylic carbon atom and by the attack angle, followed by an in-depth exploration of energy components, including strain and interaction energy. Our analysis reveals that the Bürgi-Dunitz angle emerges from a delicate balance between two key factors: strain energy and interaction energy. High strain energy, as a result of the carbonyl compound distorting to avoid Pauli repulsion, is encountered at high angles, thus setting the upper bound. On the other hand, interaction energy is shaped by a dominant Pauli repulsion when the angles are lower. This work emphasizes the value of the 2D Energy Decomposition Analysis as a refined tool, offering both quantitative and qualitative insights into chemical reactivity and selectivity.

The reactivity and endo / exo selectivity of the Diels-Alder cycloaddition reactions involving furan and substituted furans as dienes have been computationally explored. In comparison to cyclopentadiene, it is found that furan is comparatively less reactive and also less endo -selective in the reaction with maleic anhydride as the dienophile. Despite that, both the reactivity and the selectivity can be successfully modified by the presence of substituents at either 2- or 3-positions of the heterocycle. In this sense, it is found that the presence of strong electron-donor groups significantly increases the reactivity of the system while the opposite is found in the presence of electron-withdrawing groups. The observed trends in both the reactivity and selectivity are analyzed quantitatively in detail by means of the activation strain model of reactivity in combination with the energy decomposition analysis methods.

The successful architecture of active catalytic species with enhanced efficiencies is critical for the optimal exploitation of sustainable resources in industrially demanded processes. In this work, we describe the preparation of novel helical heterobimetallic Al/Mg-based complexes of the type [AlMe 2 (pbpamd - )MgR{κ 1 -O-(OC 4 H 8 O)}] [R = Et ( 1a ), t Bu ( 2a )] as potential catalysts. The design was performed through the sequential addition of the Al fragment to the ligand, followed by the Mg platform, resulting in a planar π-C 2 N 2 (sp 2 )-Al/Mg bridging core between metals. The new heterobimetallic species have been unambiguously characterized by single-crystal X-ray analysis. NOESY, DOSY, and EXSY NMR studies as well as density functional theory calculations corroborate both a rearrangement in solution to scorpionate complexes containing an unprecedented apical carbanion with a direct σ-C(sp 3 )-Al covalent bond named [{Mg(R)(pbpamd - ) Al(Me) 2 }] [R = Et ( 1b ), t Bu ( 2b )] and an interconversion equilibrium between both isomers. We verified their utility and high efficiency as catalysts in the well-controlled ring-opening polymerization of the biorenewable l- and rac -lactide (LA) at 23 °C, reaching a remarkable turnover frequency value close to 25000 h -1 for rac -LA at this temperature and exerting a significant level of heteroselectivity ( P r = 0.80). Very interestingly, the kinetics demonstrate apparent first-order with respect to the catalyst and LA, which supports a synergic intramolecular cooperation between centers with electronic modulation among them.

The Bürgi-Dunitz (BD) angle plays a pivotal role in organic chemistry to rationalize the nucleophilic addition to carbonyl groups. Yet, the origin of the obtuse trajectory of the nucleophile remains incompletely understood. Herein, we quantify the importance of the underlying physical factors quantum chemically. The obtuse BD angle appears to originate from the concerted action of a reduced Pauli repulsion between the nucleophile HOMO and carbonyl π bond, a more stabilizing HOMO-π*-LUMO(C=O) interaction, as well as a more favorable electrostatic attraction., (© 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

The physical factors governing the catalysis in Lewis acid-promoted carbonyl-ene reactions have been explored in detail quantum chemically. It is found that the binding of a Lewis acid to the carbonyl group directly involved in the transformation greatly accelerates the reaction by decreasing the corresponding activation barrier up to 25 kcal/mol. The Lewis acid makes the process much more asynchronous and the corresponding transition state less in-plane aromatic. The remarkable acceleration induced by the catalyst is ascribed, by means of the activation strain model and the energy decomposition analysis methods, mainly to a significant reduction of the Pauli repulsion between the key occupied π-molecular orbitals of the reactants and not to the widely accepted stabilization of the LUMO of the enophile.

Comprehensive computational investigations were carried out to understand the electronic and ligand properties of skeletally substituted β-diketiminate stabilized Al(I) and Ga(I) carbenoids as well as to probe their potential in small molecule activation. All of the proposed group 13 carbenoids possess a stable singlet ground state, and the majority of them have a significantly enhanced electron donation ability compared to the experimentally reported systems. The evaluation of the energetics associated with the splitting of various strong bonds such as H-H, N-H, C-F, and B-H by these carbenoids indicates that many of the proposed Al and Ga carbenoids may be considered as suitable candidates for small molecule activation.

The poorly understood factors governing the small molecule activation reactions mediated by diazaborinines have been computationally explored in detail using quantum chemical tools. To this end, the activation of E-H σ-bonds (E = H, C, Si, N, P, O, S) has been investigated. These reactions, which proceed in a concerted manner, are exergonic and, in general, associated with relatively low activation barriers. In addition, the barrier becomes lower for the E-H bonds involving the heavier element in the same group (ΔG ≠ : C>Si; N>P; O>S). This reactivity trend together with the mode of action of the diazaborinine system are quantitatively analyzed by means of the activation strain model of reactivity in combination with the energy decomposition analysis method., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

We report herein the synthesis of a bisphosphine-[NHC-BH 3 ] compound and its coordination toward gold. The ligand is shown to support a bimetallic structure bisphosphine-[NHC-BH 3 ](AuCl) 2 . The abstraction of one chloride from the gold metal center triggers the activation of a BH 3 fragment, leading to the reductive elimination of H 2 and the formation of a dicationic Au 4 2+ complex featuring Au centers at the +0.5 oxidation state, via a (μ-H)Au 2 intermediate, characterized in situ at 183 K. The reactivity of Au 4 with thiophenol led to the reoxidation of the gold metal centers to a (μ-S(Ph))Au 2 complex. In the different complexes, borane fragment was shown to bridge the Au 2 core via weak interaction with [BH], [BCl], and [BH 2 ] moieties.

Non-alternant non-benzenoid hydrocarbons exhibit very different optical and electronic properties than their well-studied benzenoid analogues. However, preparing such structures with extended conjugation length, remains challenging. Herein, we report the synthesis and properties of azuleno[2,1,8-ija]azulene derivatives using a two-step sequence involving a four-fold aldol condensation between aromatic dialdehydes and readily available tetrahydropentalene-2,5-(1H,3H)-dione. Molecules with band gap values ranging from 1.69 to 2.14 eV and molar extinction coefficients (ϵ) of nearly 3×10 5  M -1  cm -1 have been prepared. These annulene-like structures exhibit significant diatropic ring currents (aromatic), as supported by 1 H NMR spectroscopy and DFT calculations. Field-effect transistors (OFETs) using azuleno[2,1,8-ija]azulene derivatives as semiconductors exhibit charge mobility values of up to 0.05 cm 2  V -1  s -1 ., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The reaction of the oxygen-bridged frustrated Lewis pairs (FLPs) tBu 2 P-O-Si(C 2 F 5 ) 3 (1) and tBu 2 P-O-AlBis 2 (2) with azobenzene, promoted by UV irradiation, led to a selective complexation of the cis-isomer. The addition product of 2 is stable, while the adduct of 1 isomerizes in solution in an ortho-benzidine-like [3,3]-rearrangement by cleavage of the N-N bond, saturation of the nitrogen atoms with hydrogen atoms and formation of a new bond between two phenyl ortho-carbon atoms. Similar rearrangements take place with different para-substituted azobenzenes (R=Me, OMe, Cl) and di(2-naphthyl)diazene, while ortho-methylated azo compounds do not form adducts with 1. All adducts were characterized by multinuclear NMR spectroscopy and elemental analyses and the mechanism of the rearrangement was explored by quantum-chemical calculations., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Aromaticity is one of the most deeply rooted concepts in chemistry. But why, if two-thirds of existing compounds can be classified as aromatic, is there no consensus on what aromaticity is? σ-, π-, δ-, spherical, Möbius, or all-metal aromaticity… why are so many attributes needed to specify a property? Is aromaticity a dubious concept? This perspective aims to reflect where the aromaticity community is and where it is going., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

While the synthesis of nanographenes has advanced greatly in the past few years, development of their atomically precise functionalization strategies remains rare. The ability to modify the carbon scaffold translates to controlling, adjusting, and adapting molecular properties. Towards this end, here, we show that mechanochemistry is capable of transforming graphitization precursors directly into chlorinated curved nanographenes through a Scholl reaction. The halogenation occurs in a regioselective, high-yielding, and general manner. Density Functional Theory (DFT) calculations suggest that graphitization activates specific edge-positions for chlorination. The chlorine atoms allow for precise chemical modification of the nanographenes through a Suzuki or a nucleophilic aromatic substitution reaction. The edge modification enables modulation of material properties. Among the molecules prepared, corannulene-coronene hybrids and laterally fully π-extended helicenes, heptabenzo[5]superhelicenes, are particularly noteworthy., (© 2023. The Author(s).)

Scholl oxidation has become an essential reaction in the bottom-up synthesis of molecular nanographenes. Herein, we describe a Scholl reaction controlled by the electronic effects on the starting substrate (1 a, b). Anthracene-based polyphenylenes lead to spironanographenes under Scholl conditions. In contrast, an electron-deficient anthracene substrate affords a helically arranged molecular nanographene formed by two orthogonal dibenzo[fg,ij]phenanthro-[9,10,1,2,3-pqrst]pentaphene (DBPP) moieties linked through an octafluoroanthracene core. Density Functional Theory (DFT) calculations predict that electronic effects control either the first formation of spirocycles and subsequent Scholl reaction to form spironanographene 2, or the expected dehydrogenation reaction leading solely to the helical nanographene 3. The crystal structures of four of the new spiro compounds (syn 2, syn 9, anti 9 and syn 10) were solved by single crystal X-ray diffraction. The photophysical properties of the new molecular nanographene 3 reveal a remarkable dual fluorescent emission., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The potential application of η 6 -metalated aryl iodides as organocatalyst has been explored by means of computational methods. It is found that the enhanced halogen bonding donor ability of these species, in comparison with their demetalated counterparts, translates into a significant acceleration of the Diels-Alder cycloaddition reaction involving cyclohexadiene and methyl vinyl ketone. The factors behind this acceleration, the endo-exo selectivity of the process and the influence of the nature of the transition metal fragment in the activity of these species are quantitatively explored in detail by means of the combination of the Activation Strain Model of reaction and the Energy Decomposition Analysis methods., (© 2022 The Authors. Chemistry - An Asian Journal published by Wiley-VCH GmbH.)

The low electron count Pt(II) complexes [Pt(NHC')(NHC)][BAr F ] (where NHC is a N -heterocyclic carbene ligand and NHC' its metalated form) react with tertiary hydrogermanes HGeR 3 at room temperature to generate the 14-electron platinum(II) germyl derivatives [Pt(GeR 3 )(NHC) 2 ][BAr F ]. Low-temperature NMR studies allowed us to detect and characterize spectroscopically some of the σ-GeH intermediates [Pt(η 2 -HGeR 3 )(NHC')(NHC)][BAr F ] that evolve into the platinum-germyl species. One of these compounds has been characterized by X-ray diffraction studies, and the interaction of the H-Ge bond with the platinum center has been analyzed in detail by computational methods, which suggest that the main contribution is the donation of the H-Ge to a σ*(Pt-C) orbital, but backdonation from the platinum to the σ*(Ge-H) orbital is significant. Primary and secondary hydrogermanes also produce the corresponding platinum-germyl complexes, a result that contrasts with the reactivity observed with primary silanes, in which carbon-silicon bond-forming reactions have been reported. According to density functional theory calculations, the formation of Pt-Ge/C-H bonds is both kinetically and thermodynamically preferred over the competitive reaction pathway leading to Pt-H/C-Ge bonds.

In our search for new neuroprotective agents for stroke therapy to improve the pharmacological profile of the compound quinolylnitrone QN23, we have prepared and studied sixteen new, related and easily available quinolylnitrones. As a result, we have identified compounds QN4 and QN15 as promising candidates showing high neuroprotection power in a cellular experimental model of ischemia. Even though they were found to be less active than our current lead compound QN23, QN4 and QN15 provide an improved potency and, particularly for QN4, an expanded range of tolerability and improved solubility compared to the parent compound. A computational DFT-based analysis has been carried out to understand the antioxidant power of quinolylnitrones QN23, QN4 and QN15. Altogether, these results show that subtle, simple modifications of the quinolylnitrone scaffold are tolerated, providing high neuroprotective activity and optimization of the pharmacological potency required for an improved design and future drug developments in the field.

The reaction of [IrH(Cl)(κ 2 -NSi tBu2 )(coe)] ( 1 ) with 1 equiv of PCy 3 (or PH t Bu 2 ) gives the species [IrH(Cl)(κ 2 -NSi tBu2 )(L)] (L = PCy 3 , 2a ; PH t Bu 2 , 2b ), which reacts with 1 equiv of AgOTf to afford [IrH(OTf)(κ 2 -NSi tBu2 )(L)] (L = PCy 3 , 3a and PH t Bu 2 , 3b ). Complexes 2a , 2b , 3a , and 3b have been characterized by means of NMR spectroscopy and HR-MS. The solid-state structures of complexes 2a, 2b , and 3a have been determined by X-ray diffraction studies. The reversible coordination of water to 3a , 3b , and 4 to afford the corresponding adduct [IrH(OTf)(κ 2 -NSi tBu2 )(L)(H 2 O)] (L = PCy 3 , 3a -H 2 O; PH t Bu 2 , 3b -H 2 O; coe, 4 -H 2 O) has been demonstrated spectroscopically by NMR studies. The structure of complexes 3b -H 2 O and 4 -H 2 O have been determined by X-ray diffraction studies. Computational analyses of the interaction between neutral [NSi tBu2 ] • and [Ir( H )L(X)] • fragments in Ir-NSi tBu2 species confirm the electron-sharing nature of the Ir-Si bond and the significant role of electrostatics in the interaction between the transition metal fragment and the κ 2 -NSi t Bu2 ligand. The activity of Ir-(κ 2 -NSi tBu2 ) species as catalysts for the hydrolysis of HSiMe(OSiMe 3 ) 2 depends on the nature of the ancillary ligands. Thus, while the triflate derivatives are active, the related chloride species show no activity. The best catalytic performance has been obtained when using complexes 3a , with triflate and PCy 3 ligands, as a catalyst precursor, which allows the selective obtention of the corresponding silanol.

The ambiguous bonding situation of σ-E-H (E=Si, B) complexes in transition metal compounds has been rationalized by means of Density Functional Theory calculations. To this end, the combination of the Energy Decomposition Analysis (EDA) method and its Natural Orbital for Chemical Valance (NOCV) extension has been applied to representative complexes described in the literature where the possible η 1 versus η 2 coordination mode is not unambiguously defined. Our quantitative analyses, which complement previous data based on the application of the Quantum Theory of Atoms in Molecules (QTAIM) approach, indicate that there exists a continuum between genuine η 1 and η 2 modes depending mainly on the strength of the backdonation. Finally, we also applied this EDA-NOCV approach to related main-group species where the backdonation is minimal., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Bimetallic motifs mediate the selective activation and functionalization of CO 2 in metalloenzymes and some recent synthetic systems. In this work, we build on the nascent concept of bimetallic frustrated Lewis pairs (FLPs) to investigate the activation and reduction of CO 2 . Using the Fe 0 fragment [(depe) 2 Fe] (depe=1,2-bis(diethylphosphino)ethane) as base, we modify the nature of the partner Lewis acid to accomplish a divergent and highly chemoselective reactivity towards CO 2 . [Au(PMe 2 Ar)] + irreversibly dissociates CO 2 , Zn(C 6 F 5 ) 2 and B(C 6 F 5 ) 3 yield different CO 2 adducts stabilized by push-pull interactions, while Al(C 6 F 5 ) 3 leads to a rare heterobimetallic C-O bond cleavage, and thus to contrasting reduced products after exposure to dihydrogen. Computational investigations provide a rationale for the divergent reactivity, while Energy Decomposition Analysis-Natural Orbital for Chemical Valence (EDA-NOCV) method substantiates the heterobimetallic bonding situation., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A new methodology for the synthesis of seven-membered unsaturated azacycles (tetrahydroazepines) was developed. It is based on the powerful aza-Prins cyclization in combination with the Peterson-type elimination reaction. In a single reaction step, a C-N, C-C bond and an endocyclic double bond are formed. Under mild reaction conditions and using iron(III) salts as sustainable catalysts, tetrahydroazepines with different degrees of substitution are obtained directly and efficiently. DFT calculations supported the proposed mechanism.

Bacterial transposons are pervasive mobile genetic elements that use distinct DNA-binding proteins for horizontal transmission. For example, Escherichia coli Tn7 homes to a specific attachment site using TnsD 1 , whereas CRISPR-associated transposons use type I or type V Cas effectors to insert downstream of target sites specified by guide RNAs 2,3 . Despite this targeting diversity, transposition invariably requires TnsB, a DDE-family transposase that catalyses DNA excision and insertion, and TnsC, a AAA+ ATPase that is thought to communicate between transposase and targeting proteins 4 . How TnsC mediates this communication and thereby regulates transposition fidelity has remained unclear. Here we use chromatin immunoprecipitation with sequencing to monitor in vivo formation of the type I-F RNA-guided transpososome, enabling us to resolve distinct protein recruitment events before integration. DNA targeting by the TniQ-Cascade complex is surprisingly promiscuous-hundreds of genomic off-target sites are sampled, but only a subset of those sites is licensed for TnsC and TnsB recruitment, revealing a crucial proofreading checkpoint. To advance the mechanistic understanding of interactions responsible for transpososome assembly, we determined structures of TnsC using cryogenic electron microscopy and found that ATP binding drives the formation of heptameric rings that thread DNA through the central pore, thereby positioning the substrate for downstream integration. Collectively, our results highlight the molecular specificity imparted by consecutive factor binding to genomic target sites during RNA-guided transposition, and provide a structural roadmap to guide future engineering efforts., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)