Palladium-Catalyzed Sequential Cross-Coupling/Annulation of ortho-Vinyl Bromobenzene with Aryl Bromide: Bimetallic Pathway versus Pd(II)-Pd(IV) Pathway: A DFT Investigation.

The palladium-catalyzed sequential cross-coupling/annulation of ortho-vinyl bromobenzenes with aryl bromides generating phenanthrenes was characterized by density functional theory (DFT). The Pd(II)-Pd(IV) pathway (Path V) is shown to be less probable than the bimetallic pathway (Path I), the latter proceeding via the following six steps: oxidative addition, vinyl-C(sp2)-H activation, Pd(II)-Pd(II) transmetalation, C-C coupling, aryl-C(sp2)-H activation, and reductive elimination. The aryl-C(sp2)-H activation process acts as the rate-determining step (RDS) of the entire chemical transformation, with an activation free energy barrier of ca. 27.4-28.8 kcal·mol-1, in good agreement with the corresponding experimental data (phenanthrenes' yields of ca. 65-90% at 130 °C after 5 h of reaction). The K2CO3 additive effectively reduces the activation free energy barrier of the RDS through direct participation in the reaction while preferentially modulating the charge distributions and increasing the stability of corresponding intermediates and complexes along the reaction path. Furthermore, bonding and electronic structure analyses of the key structures indicate that the chemo- and regioselectivities of the reaction are strongly influenced by both electronic effects and steric hindrance.

Mechanical and Lattice Thermal Properties of Si-Ge Lateral Heterostructures.

Two-dimensional (2D) materials have drawn extensive attention due to their exceptional characteristics and potential uses in electronics and energy storage. This investigation employs simulations using molecular dynamics to examine the mechanical and thermal transport attributes of the 2D silicene-germanene (Si-Ge) lateral heterostructure. The pre-existing cracks of the Si-Ge lateral heterostructure are addressed with external strain. Then, the effect of vacancy defects and temperature on the mechanical attributes is also investigated. By manipulating temperature and incorporating vacancy defects and pre-fabricated cracks, the mechanical behaviors of the Si-Ge heterostructure can be significantly modulated. In order to investigate the heat transport performance of the Si-Ge lateral heterostructure, a non-equilibrium molecular dynamics approach is employed. The efficient phonon average free path is obtained as 136.09 nm and 194.34 nm, respectively, in the Si-Ge heterostructure with a zigzag and armchair interface. Our results present the design and application of thermal management devices based on the Si-Ge lateral heterostructure.

Nickel-Catalyzed Three-Component Unsymmetrical Bis-Allylation of Alkynes with Alkenes: A Density Functional Theory Study.

Density functional theory (DFT) characterizations were employed to resolve the structural and energetic aspects and product selectivities along the mechanistic reaction paths of the nickel-catalyzed three-component unsymmetrical bis-allylation of alkynes with alkenes. Our putative mechanism initiated with the in situ generation of the active catalytic species [Ni(0)L2] (L = NHC) from its precursors [Ni(COD)2, NHC·HCl] to activate the alkyne and alkene substrates to form the final skipped trienes. This proceeds via the following five sequential steps: oxidative addition (OA), ß-F elimination, ring-opening complexation, C-B cleavage and reductive elimination (RE). Both the OA and RE steps (with respective free energy barriers of 24.2 and 24.8 kcal·mol-1) contribute to the observed reaction rates, with the former being the selectivity-controlling step of the entire chemical transformation. Electrophilic/nucleophilic properties of selected substrates were accurately predicted through dual descriptors (based on Hirshfeld charges), with the chemo- and regio-selectivities being reasonably predicted and explained. Further distortion/interaction and interaction region indicator (IRI) analyses for key stationary points along reaction profiles indicate that the participation of the third component olefin (allylboronate) and tBuOK additive played a crucial role in facilitating the reaction and regenerating the active catalyst, ensuring smooth formation of the skipped triene product under a favorably low dosage of the Ni(COD)2 catalyst (5 mol%).

Impacts of defects on the mechanical and thermal properties of SiC and GeC monolayers.

Defect engineering has been considered as an effective way for controlling the heat transport properties of two-dimensional materials. In this work, the effects of point vacancies and grain boundaries on the mechanical and thermal performances of SiC and GeC monolayers are investigated systematically by molecular dynamics calculations. The failure strength in SiC and GeC is decreased by introducing vacancies at room temperature, and the stress-strain relationship can be tuned significantly by different kinds of vacancies. When the grain boundary of 21.78° is applied, the maximal fracture strengths can be as large as 27.56% for SiC and 23.56% for GeC. Also, the thermal properties of the two monolayers show a remarkable dependence on the vacancies and grain boundaries. The high vacancy density in SiC and GeC can induce disordered heat flow and the C/Ge point defect is crucial for thermal conductivity regulation for the Si/GeC monolayer. More importantly, the SiC and GeC monolayers with a grain boundary of 5.09° show excellent interfacial thermal conductance. Our findings are of great importance in understanding SiC and GeC monolayers and seeking their potential applications.

Electronic and Steric Control of Rates and Selectivities in Rhodium-Catalyzed [2+2+2] Cycloadditions for Constructing Fused Tricyclic Hydronaphthofurans: A Density Functional Theory Study.

Fused tricyclic hydronaphthofurans with multiple chiral centers are very important skeletons for constructing natural products; however, their synthesis is challenging, and a detailed understanding of the final formation mechanism remains elusive. In this work, density functional theory computations were employed to characterize rhodium-catalyzed [2+2+2] cycloaddition of enyne with terminal alkynes. The putative mechanism involves an initial ligand exchange, followed by oxidative cyclization, olefin insertion, and reductive elimination processes. Oxidative cyclization is shown to be the rate- and selectivity-determining step of the full chemical transformation, where the R substituent on terminal alkynes has a significant influence on the reaction selectivities. When R is an electron-donating group (OMe and Me), the ortho-substituted tricyclic hydronaphthofurans (P1) are predicted to be dominant; on the contrary, meta-substituted compounds P2 emerge as the main products when R is an electron-withdrawing group (NO2, CF3, and CN). Computational predictions for selectivity are in good agreement with experimental product ratios. Free energy barriers of the rate-determining step for P1 and P2 are ∼22.3-23.6 kcal mol-1, which align well with their experimental yields of ∼79-92% at 313 K after 0.5 h. The results also accurately reproduce experimentally observed regio-, chemo-, and enantioselectivities, with steric hindrance as well as electronic properties of the substrate and ligand markedly influencing the reaction rates and selectivities. The influence of computational methods is also explored and discussed in detail.

Multi-Pathway Consequent Chemoselectivities of CpRuCl(PPh3 )2 /MeI-Catalysed Norbornadiene Alkyne Cycloadditions.

Chemoselectivities of five experimentally realised CpRuCl(PPh3 )2 /MeI-catalysed couplings of 7-azabenzo-norbornadienes with selected alkynes were successfully resolved from multiple reaction pathway models. Density functional theory calculations showed the following mechanistic succession to be energetically plausible: (1) CpRuI catalyst activation; (2) formation of crucial metallacyclopentene intermediate; (3) cyclobutene product (P2) elimination (ΔGRel(RDS) ≈11.9-17.6 kcal mol-1 ). Alternative formation of dihydrobenzoindole products (P1) by isomerisation to azametalla-cyclohexene followed by subsequent CpRuI release was much less favourable (ΔGRel(RDS) ≈26.5-29.8 kcal mol-1 ). Emergent stereoselectivities were in close agreement with experimental results for reactions a, b, e. Consequent investigations employing dispersion corrections similarly support the empirical findings of P1 dominating in reactions c and d through P2→P1 product transformations as being probable (ΔG≈25.3-30.1 kcal mol-1 ).

Competing Mechanisms, Substituent Effects, and Regioselectivities of Nickel-Catalyzed [2 + 2 + 2] Cycloaddition between Carboryne and Alkynes: A DFT Study.

Competing reaction mechanisms, substituent effects, and regioselectivities of Ni(PPh3)2-catalyzed [2 + 2 + 2] carboryne-alkyne cycloadditions were characterized by density functional theory using the real chemical systems and solvent effects considered. A putative mechanism involving the following steps was characterized: (1) exothermic carboryne-catalyst complexation and nucleophilic attack by the first alkyne; (2) insertion of the second alkyne, the rate-determining step (RDS) in all four reactions studied; (3) isomerization of reactant-bound complexes; and (4) product elimination and catalyst regeneration. The RDS in three reactions is mediated by free energy barriers of 27.2, 31.1, and 36.6 kcal·mol(-1), representative of the corresponding experimental yields of 67, 54, and 33%, respectively. A fourth reaction with 0% experimental yield showed representative RDS free energy barriers of 60.4 kcal·mol(-1), which are difficult to surmount even at 90 °C. Alternative pathways leading to differing isomers were similarly characterized and successfully reproduced experimentally determined product regioselectivities. Kinetic data derived from free energy barriers are in quantitative agreement (< ± 0.75-3.0 kcal·mol(-1)) of the experimental times, affirming the theoretical results as representative of the real chemical transformations. Complementary determinations show the use of truncated models (Ni(PMe3)2, Ni(PH3)2) causes the RDS to vary from step 2 (alkyne insertion) to step 1 (alkyne attack), highlighting the need to employ real chemical systems in modeling these reactions.

The prediction of two-dimensional PbN: opened bandgap in heterostructure with CdO.

The development of two-dimensional (2D) materials has received wide attention as a generation of optoelectronics, thermoelectric, and other applications. In this study, a novel 2D material, PbN, is proposed as an elemental method using the prototype of a recent reported nitride (J. Phys. Chem. C 2023, 127, 43, 21,006-21014). Based on first-principle calculations, the PbN monolayer is investigated as stable at 900 K, and the isotropic mechanical behavior is addressed by the Young's modulus and Poisson's ratio at 67.4 N m-1 and 0.15, respectively. The PbN monolayer also presents excellent catalytic performance with Gibbs free energy of 0.41 eV. Zero bandgap is found for the PbN monolayer, and it can be opened at about 0.128 eV by forming a heterostructure with CdO. Furthermore, the PbN/CdO is constructed by Van der Waals interaction, while the apparent potential drop and charge transfer are investigated at the interface. The PbN/CdO heterostructure also possesses excellent light absorption properties. The results provide theoretical guidance for the design of layered functional materials.

Stacking engineering induced Z-scheme MoSSe/WSSe heterostructure for photocatalytic water splitting.

Stacking engineering is a popular method to tune the performance of two-dimensional materials for advanced applications. In this work, Jansu MoSSe and WSSe monolayers are constructed as a van der Waals (vdWs) heterostructure by different stacking configurations. Using first-principle calculations, all the relaxed stacking configurations of the MoSSe/WSSe heterostructure present semiconductor properties while the direct type-II band structure can be obtained. Importantly, the Z-scheme charge transfer mode also can be addressed by band alignment, which shows the MoSSe/WSSe heterostructure is an efficient potential photocatalyst for water splitting. In addition, the built-in electric field of the MoSSe/WSSe vdWs heterostructure can be enhanced by the S-Se interface due to further asymmetric structures, which also results in considerable charge transfer comparing with the MoSSe/WSSe vdWs heterostructure built by the S-S interface. Furthermore, the excellent optical performances of the MoSSe/WSSe heterostructure with different stacking configurations are obtained. Our results provide a theoretical guidance for the design and control of the two-dimensional heterostructure as photocatalysts through structural stacking.

Liquid-Metal Molecular Scissors.

Molecules are the smallest units of matter that can exist independently, relatively stable, maintaining their physical and chemical activities. The key factors that dominate the structures and properties of molecules include atomic species, alignment commands, and chemical bonds. Herein, we reported a generalized effect in which liquid metals can directly cut off oxygen-containing groups in molecular matter at room temperature, allowing the remaining groups to recombine to form functional materials. Thus, we propose basic liquid-metal scissors for molecular directional clipping and functional transformations. As a proof of concept, we demonstrate the capabilities of liquid-metal scissors and reveal that the gallium on the surface of liquid metals directly extracts oxygen atoms from H2O or CH3OH molecules to form oxides. After clipping, the remaining hydrogen atoms from the H2O molecules recombine to form H2, while the remaining fragments of CH3OH produce H2, carbon materials, and carboxylates. This finding refreshes our basic understanding of chemistry and should lead to the development of straightforward molecular weaving techniques, which can help to overcome the limitations of molecular substances with single purposes. It also opens a universal route for realizing future innovations in molecular chemical engineering, life sciences, energy and environment research, and biomedicine.

Directly Printable Flexible Optoelectronics through Surface Atomic Modification of Liquid Metals at Room Temperature.

Flexible optoelectronics have fully demonstrated their transformative roles in various fields, but their fabrication and application have been limited by complex processes. Liquid metals (LMs) are promising to be ideal raw materials for making flexible optoelectronics due to their extraordinary fluidity and printability. Herein, we propose a painting-modifying strategy based on solution processability for directly printing out fluorescent flexible optoelectronics from LMs via surface modification. The LMs of eGaIn, which were obtained by the mixing of gallium with indium metal spheres, were used as ink to paint high-finesse patterns on flexible substrates. Through introducing surface modification of LMs, the gallium atom on the surface of the LMs was directly transformed into the composite fluorescent functional layers of GaO(OH) and GaN after being modified with an ammonia aqueous solution. Owing to painting, this strategy is not limited by any curved surfaces, shapes, or facilities and has excellent adaptability. Particularly, the fluorescent layers were obtained through a spontaneous, instantaneous, and solution-processable process that is environmentally friendly, easy to administrate, recyclable, and adjustable. The present finding breaks through the limitations of LMs in making flexible optoelectronics and provides strategies for addressing severe challenges facing existing materials and flexible optoelectronics. This method is expected to be very useful for fabricating flexible lights, transformable displays, intelligent anticounterfeiting devices, skin-inspired optoelectronics, and chameleon-biomimetic soft robots in the coming time.

A new natural naphtho[1,2-b]furan from the leaves of Cassia fistula.

A new naphtho[1,2-b]furan, 2,9-dihydroxy-7-methoxy-4-methylnaphtha[1,2-b]furan-3(2H)-one (1), along with 10 known compounds vanillic acid (2), naringenin (3), glyceryl-1-tetracosanoate (4), moracin J (5), 1,3,8-trihydroxyanthraquinone (6), esculetin (7), mauritianin (8), kaempferol 3-neohesperidoside (9), ß-sitosterol (10), and ß-daucosterol (11), was isolated from the leaves of Cassia fistula. The structure of the new compound was determined by NMR and X-ray analysis. Compounds 1, 3, 5-9 were isolated from this plant for the first time. The naphtha[1,2-b]furan was firstly isolated from the natural resources.

Pd-NHC catalysed regioselective activation of B(3,6)-H of o-carborane - a synergy between experiment and theory.

Regioselective B-H activation of o-carboranes is an effective way for constructing o-carborane derivatives, which have broad applications in medicine, catalysis and the wider chemical industry. However, the mechanistic basis for the observed selectivities remains unresolved. Herein, a series of density functional theory (DFT) calculations were employed to characterise the palladium N-heterocyclic carbene (Pd-NHC) catalysed regioselective B(3,6)-diarylation of o-carboranes. Computational results at the IDSCRF(ether)-LC-ωPBE/BS1 and IDSCRF(ether)-LC-ωPBE/BS2 levels showed that the reaction undergoes a Pd(0) → Pd(II) → Pd(0) oxidation/reduction cycle, with the regioselective B(3)-H activation being the rate-determining step (RDS) for the full reaction profile. The computed RDS free energy barrier of 24.3 kcal mol-1 agrees well with the 82% yield of B(3,6)-diphenyl-o-carborane in ether solution at 298 K after 24 hours of reaction. The Ag2CO3 additive was shown to play a crucial role in lowering the RDS free energy barrier and facilitating the reaction. Natural charge population (NPA) and molecular surface electrostatic potential (ESP) analyses successfully predicted the experimentally observed regioselectivities, with electronic effects being revealed to be the dominant contributors to product selectivity. Steric hindrance was also shown to impact the reaction rate, as revealed by experimental and computational characterisation studies of substituents and ligand effects. Furthermore, computational predictions aligned with the experimental findings that NHC ligands outperform the phosphine ones for this particular reaction. Overall, the observed trends reported in this work are expected to assist in the rational optimisation of the efficiency and regioselectivity of this and related reactions.

Gelatin Methacryloyl-Based Sponge with Designed Conical Microchannels for Rapidly Controlling Hemorrhage and Theoretical Verification.

It remains a challenge to develop effective hemostatic products in battlefield rescue for noncompressible massive hemorrhage. Some previous research had concentrated on the modification of different materials to improve the hemostasis ability of sponges. Herein, to investigate the relationship between the taper of microchannels and hemostatic performance of porous sponges, gelatin methacryloyl-based sponges with designed conical microchannels and a disordered porous structure were prepared using the 3D printing method and freeze-drying technology. Experiments and theoretical model analysis demonstrated that the taper and distribution of microchannels in the sponge affected the water and blood absorption properties, as well as the expansion ability. In treatment of SD rat liver defect and SD rat liver perforation wound, GS-1 sponge with the taper (1/15) microchannels exhibited an excellent hemostatic effect with blood loss of 0.866 ± 0.093 g and a hemostasis time of 280 ± 10 s. Results showed that the hemostatic capacities of GelMA sponges were increased with the bottom diameter (taper) of conical microchannels. This is a potential strategy to develop designed taper sponges with designed taper microchannels for rapidly controlling hemorrhage.

Understanding the Optimal Cooperativity of Human Glucokinase: Kinetic Resonance in Nonequilibrium Conformational Fluctuations.

The cooperativity of a monomeric enzyme arises from dynamic correlation instead of spatial correlation and is a consequence of nonequilibrium conformation fluctuations. We investigate the conformation-modulated kinetics of human glucokinase, a monomeric enzyme with important physiological functions, using a five-state kinetic model. We derive the non-Michealis-Menten (MM) correction term of the activity (i.e., turnover rate), predict its relationship to cooperativity, and reveal the violation of conformational detailed balance. Most importantly, we reproduce and explain the observed resonance effect in human glucokinase (i.e., maximal cooperativity when the conformational fluctuation rate is comparable to the catalytic rate). With the realistic parameters, our theoretical results are in quantitative agreement with the reported measurement by Miller and co-workers. The analysis can be extended to a general chemical network beyond the five-state model, suggesting the generality of kinetic cooperativity and resonance.

Synthesis, characterization, photoinduced isomerization, and spectroscopic properties of vinyl-1,8-naphthyridine derivatives and their copper(I) complexes.

A series of 1,8-naphthyridine derivatives containing vinyl, 2-(2-acetylamino-pyridine-6-ethylene)-4-methyl-7-acetylamino-1,8-naphthyridine (L(1)), 2-(2-acetylamino-pyridine-6-ethylene)-1,8-naphthyridine (L(2)), 2-(2-acetylamino-pyridinyl-6-ethylene)-4-methyl-7-hydroxyl-1,8-naphthyridine (L(3)), 2-(2-diacetylamino-pyridinyl-3-ethylene)-7-diacetylamino-1,8-naphthyridine (L(4)), and 7-(2-diacetylamino-pyridinyl-3-ethylene)-4'-acetyl-pyrrolo[1',5'-a]-1,8-naphthyridine (L(5)), as well as complexes [CuL(1)(PCy(3))](BF(4))(2) (1) (PCy(3) = tricyclohexylphosphine), [Cu(2)L(1)(PPh(3))(4)](BF(4))(2) (2) (PPh(3) = triphenylphosphine), [Cu(2)L(1)(dppm)](BF(4))(2) (3) (dppm = bis(diphenylphosphino)methane), and [Cu(2)(L(1))(dcpm)][BF(4)](2) (4) (dcpm = bis(dicyclohexylphosphino)methane, were synthesized. All these compounds, except for L(1) and L(2), were characterized by single crystal X-ray diffraction analysis, and a comprehensive study of their spectroscopic properties involving experimental theoretical studies is presented. We found an intramolecular 1,3-hydrogen transfer during the formation of L(3) and L(4), which in the case of the latter plays an important role in the 1,5-dipolar cyclization of L(5). The spectral changes that originate from an intramolecular charge transfer (ICT) in the form of a pi(py)-->pi*(napy) transition can be tuned through acid/base-controlled switching for L(1)-L(3). A photoinduced isomerization for L(1)-L(3), 1, and 2 having flexible structures was observed under 365 nm light irradiation. Quantum chemical calculations revealed that the dinuclear complexes with structural asymmetry exhibit different metal-to-ligand charge-transfer transitions.

Density functional theory investigation of the alkyl-alkyl Negishi cross-coupling reaction catalyzed by N-heterocyclic carbene (NHC)-Pd complexes.

A novel mechanism is proposed for the Pd-1,3-(2,6-diisopropylphenyl)imidazolyl-2-ylidene (1) catalyzed Negishi reaction. DFT computations supported by atoms-in-molecules (AIM) analyses of non-truncated models show that a "steric wall" created by the N-substituent on the ligand guides reactants to and from the Pd center. Notably, transmetalation and not oxidative addition is found to be rate-limiting. Additionally, a key Pd-Zn interaction (approximately = 2.4 A, rho(b) approximately = 0.0600 au) is identified in the mechanism. This interaction persists beyond reductive elimination and, in combination with the ligand, facilitates reductive elimination by creating a highly sterically crowded environment in the coordination sphere of the Pd center.

Electronic Effect-Guided, Palladium-Catalyzed Regioselective B-H Activation and Multistep Diarylation of o-Carboranes with Aryl Iodides.

Density functional theory calculations at IDSCRF-B3LYP/DZVP computational level were conducted on palladium-catalyzed regioselective B-H activation and diarylation of o-carboranes with aryl iodides in solution. Computational results indicate that this reaction follows a multistep mechanism and needs to get over several transition states before the final B(4,5)-diarylated o-carborane derivatives are formed. B-H activation, oxidation addition, and successive reduction of the Pd(II) catalyst involving a Pd(II)-Pd(IV)-Pd(II) catalytic cycle has been confirmed, in which AgOAc plays a crucial role. Electron-donating group on the cage carbon of o-carboranes is verified to be beneficial for its B-H activation and diarylation, while steric hindrance between the aryl and o-carboranyl groups retards it. Natural population analysis and Gibbs free energetic results predict consistent regioselectivities with experiments and manifest the pivotal role of electronic effect in controlling regioselective B-H activation of o-carboranes. These results are expected to shed some light on further improvement of experimental conditions and better controlling of regioselectivities.

High level ab initio exploration on the conversion of carbon dioxide into oxazolidinones: the mechanism and regioselectivity.

Density functional theory (DFT) and second order Møller-Plesset perturbation (MP2) calculations, employing the 6-311++G(d,p) basis set, were carried out on alkyl-substituted aziridines to explore the reaction mechanisms and regioselectivity associated with their ring-opening conversions to oxazolidinones, in the presence of carbon dioxide. Computational results, employing the self-consistent reaction field polarizable continuum model (SCRF(PCM/Bader)), indicated that the conversions proceed with thermodynamic ease in THF solvent at room temperature. It is proposed that the N-alkylaziridine promotes ring opening through a SN2 attack of the iodide ion, of catalytic lithium iodide, on the preformed complex. The oxazolidinone regioisomer ratio is highly sensitive to aziridine ring-carbon substitution. Therein, monophenyl substitutions show preference to opening more highly substituted carbon-nitrogen bonds, providing rationale as to why experimental works result in an exclusive oxazolidinone regioisomer product.

The pivotal role of electronics in preferred alkene over alkyne Ni-carboryne insertions and absolute regioselectivities.

The in situ formation mechanisms of active Ni-carboryne species (COM1) and subsequent alkene/alkyne Ni-C bond insertion priorities, as well as relevant cycloaddition regioselectivities and kinetics, were investigated using the IDSCRF-B3LYP density functional theory (DFT) method, and all atoms were equitably treated at the DGDZVP level. The results reveal the o-carborane species to be energetically hedged into a four-step path (barrier heights 5.3, 19.7, 18.4 and 0.3 kcal mol-1, respectively) prior to being transferred into the active Ni-carboryne species (COM1) with the assistance of nBuLi and NiCl2(PPh3)2 at room temperature. In direct agreement with empirical trends, alkene insertion into Ni-C bonds on COM1 is exclusively favoured over the competing alkyne insertion. Electronic structure analyses of the corresponding transition structures showed that the preference of alkenes to alkynes is due to different bonding characteristics during this insertion process, namely, back donation for alkenes but donation for alkyne insertion, as evidenced by molecular graphics and NBO charge distributions. Subsequent alkyne additions (i.e. post alkene insertion) arise as the rate-determining step (RDS) for each of the five different reactions (a-e) explored. The solution free-energy barriers of these RDSs (30.5-38.5 kcal mol-1) were in quantitative agreement with their corresponding experimental yields, evidencing the reliability of the DFT results to reproduce chemical phenomena and energetic trends in real Ni-catalysed carboryne-alkene/alkyne cycloadditions.