Synthesis, IR spectra, and solid-state luminescence of triphenylguanidinium salts with the anions B10H 10 2− , B12H 12 2− , B9C2H 12 2− , [Co(C2B9H11)2]−, and [Ni(C2B9H11)2]−

Triphenylguanidinium Ph₃GH⁺ salts with the anions B₁₀H ₁₀ ^2? , B₁₂H ₁₂ ^2? , B₉C₂H ₁₂ ^2? , [Co(C₂B₉H₁₁)₂]^?, and [Ni(C₂B₉H₁₁)₂]^? were synthesized and described by DTA, IR spectroscopy, and solid-state luminescence. By IR spectroscopy, it was shown that intermolecular interactions involving the NH groups of the cation are enhanced in the sequence [Co(C₂B₉H₁₁)₂]^? ～ [Ni(C₂B₉H₁₁)₂]^? < B₉C₂H ₁₂ ^2? < B₁₂H ₁₂ ^2? < B₁₀H ₁₀ ^2? .     

Theoretical study of dodecahydro-closo-decaborane B10H12, the diprotonated boron cluster B10H 10 2−

The electronic and geometric structures of different isomers of the closo-B₁₀H₁₂ boron cluster have been calculated by the density functional theory method (in the B3LYP/6-311++G**//B3LYP/6-31G* approximation). The compound is considered to be the diprotonated (H*) analogue of the well-studied B₁₀H ₁₀ ^2? anion and serves as a model system. The increase in the relative energies of isomers and the preferred location of the extra H* protons near the opposite B(1) and B(10) “poles” are consistent with the charge separation (in the framework of the Mulliken population analysis) between B(1) and B(10). The reactions of migration of one or simultaneously two H* protons in B₁₀H₁₂ over the boron polyhedron have been considered, and the corresponding energies of elementary events E and activation barriers h have been estimated. The elementary events have been predicted in which both H* protons simultaneously move along the trajectories near the opposite B(1) and B(10) poles of the B₁₀H ₁₀ ^2? polyhedron with the same or opposite changes in the angles determining the H* position with respect to the B(1)–B(10) axis. The activation barrier to the “opposite” migration of the H* protons has been assessed to be h ～ 1.2 kcal/mol, whereas for the migration of the H* protons in the same direction, h ～ 1.4 kcal/mol. The H* proton transfer from the position near the B(1) pole to the position near the opposite B(10) pole is hindered, and higher activation barriers on the order of h ～ 13–15 kcal/mol should be overcome for this transfer to occur.     

Metal-Free Intermolecular C−H Borylation of N-Heterocycles at B−B Multiple Bonds

Carbene-stabilized diborynes of the form LBBL (L=N-heterocyclic carbene (NHC) or cyclic alkyl(amino)carbene (CAAC)) induce rapid, high yielding, intermolecular ortho-C−H borylation at N-heterocycles at room temperature. A simple pyridyldiborene is formed when an NHC-stabilized diboryne is combined with pyridine, while a CAAC-stabilized diboryne leads to activation of two pyridine molecules to give a tricyclic alkylideneborane, which can be forced to undergo a further H-shift resulting in a zwitterionic, doubly benzo-fused 1,3,2,5-diazadiborinine by heating. Use of the extended N-heteroaromatic quinoline leads to a borylmethyleneborane under mild conditions via an unprecedented boron-carbon exchange process.     

S−H…O and O−H…O Hydrogen Bonds-Comparison of Dimers of Thiocarboxylic and Carboxylic Acids

ωB97-XD/aug-cc-pVTZ calculations were performed on dimers of selected thiocarboxylic acids and on analogous carboxylic acids. The sample of calculated thiocarboxylic acids is an extension of the Cambridge Structural Database search that contains only a few such structures. The Natural Bond Orbital (NBO) method, Symmetry-Adapted Perturbation Theory (SAPT) approach, Non-Covalent Interaction (NCI) method and Quantum Theory of Atoms in Molecules (QTAIM) were applied additionally to analyse interactions in dimers of thiocarboxylic and carboxylic acids. The insights into crystal structures as well as into results of calculations show that the formation of S−H…O hydrogen bonds between molecules of thiocarboxylic acids is steered by the same mechanisms as the formation of much stronger O−H…O hydrogen bonds in carboxylic acids. The intramolecular O−H…O and C−H…S hydrogen bonds occurring in few considered structures are also analysed.     

Palladium-Catalyzed Atroposelective Kinetic C−H Olefination and Allylation for the Synthesis of C−B Axial Chirality

The direct C−H functionalization of 1,2-benzazaborines, especially asymmetric version, remains a great challenge. Here we report a palladium-catalyzed enantioselective C−H olefination and allylation reactions of 1,2-benzazaborines. This asymmetric approach is a kinetic resolution (KR), providing various C−B axially chiral 2-aryl-1,2-benzazaborines and 3-substituted 2-aryl-1,2-benzazaborines in generally high yields with excellent enantioselectivities (selectivity (S) factor up to 354). The synthetic potential of this reaction is showcased by late-stage modification of complex molecules, scale-up reaction, and applications.     

Rhoda-Electrocatalyzed C−H Methylation and Paired Electrocatalyzed C−H Ethylation and Propylation

The use of electricity over traditional stoichiometric oxidants is a promising strategy for sustainable molecular assembly. Herein, we describe the rhoda-electrocatalyzed C−H activation/alkylation of several N-heteroarenes. This catalytic approach has been successfully applied to several arenes, including biologically relevant purines, diazepam, and amino acids. The versatile C−H alkylation featured water as a co-solvent and user-friendly trifluoroborates as alkylating agents. Finally, the rhoda-electrocatalysis with unsaturated organotrifluoroborates proceeded by paired electrolysis.     

Iodination of B12H11OC(O)CH2–3, B12H11OH2–, and B12H11SCN2–

Reactions of iodination of monosubstituted derivatives of B₁₂H₁₁X^2–anion (X = OC(O)CH₃, OH, SCN) were studied. The reactions were shown to proceed smoothly to give B₁₂H₁₀(OC(O)CH₃)I^2–((carboxy)(iodo)[decahydro[I _h1551-²⁰-closo]dodecaborate(2–)] anion), B₁₂H₁₀(OH)I^2–((hydroxo)(iodo)[decahydro[I _h1551-²⁰-closo]dodecaborate(2–)] anion), and B₁₂H₁₀(SCN)I^2–((thiocyanato)(iodo)[decahydro[I _h1551-²⁰-closo]dodecaborate(2–)] anion) in high yields, irrespective of the solvent used (benzene, H₂O–ROH, where R = C₂H₅, CH₂CH₂CH₃).¹     

Isomerization of B6, B6 − and B6 + clusters

The interconversions between isomers with the same spin multiplicity of neutral B₆ and charged B₆ ^? and B₆ ⁺ clusters have been investigated at the B3LYP/6-311+G* level of theory, including determination of the minimum energy pathways with transition states connecting the corresponding reactants and products. In dynamic calculations, 26 isomers were optimized, including 11 novel isomers. In order to further refine the energies, single-point B3LYP/6-311+G(3df) calculations were carried out on the corresponding B3LYP/6-311+G* geometries of all isomers of B₆, B₆ ^? and B₆ ⁺ and the corresponding isomerization transition states. The stability of each isomer of B₆ (singlet and triplet states), B₆ ^? (doublet state) and B₆ ⁺ (doublet state) was analyzed from both thermodynamic and dynamic viewpoints.     

Electrochemical Direct C−H Halogenation of N-Heteroarenes and Naphthols

In this study, we present a straightforward and environmentally friendly electrochemical approach for achieving selective halogenation of N-heteroarenes, including indoles, diazoles, pyrroles, quinolinone, and naphthols. Our method utilizes commercially available and affordable ammonium halides as halogen source. A library of valuable halogenated N-heteroarenes can be synthesized in moderate to excellent yields under mild conditions (transition-metal-free, oxidant-free, ethanol as solvent, atmospheric environment). The approach demonstrates a broad substrate scope, excellent tolerance towards various functional groups, and scalability.     

meta-Selective C−H Arylation of Fluoroarenes and Simple Arenes

Fluorine is known to promote ortho-C−H metalation. Based upon this reactivity, we employed an activated norbornene that traps the ortho-palladation intermediate and is then relayed to the meta position, leading to meta-selective C−H arylation of fluoroarenes. Deuterium experiment suggests that this meta-arylation is initiated by ortho C−H activation and the catalytic cycle is terminated by C-2 protonation. A dual-ligand system is crucial for the observed high reactivity and site selectivity. Applying this approach to simple benzene or other arenes also affords arylation products with good yield and site selectivity.     

Nonempirical calculations of the potential-energy fields of the nucleophilic addition of H− and F− to acetylene and methylacetylene molecules

By using the basis 3–21 + G, the minimum-energy routes for the nucleophilic addition to the F^– ion to methylacetylene have been calculated within the framework of the Hartree-Fock-Roothaan method according to and against the Markovnikov rule with the formation of the 1-fluoropropenyl and 2-fluoropropenyl anions. The results have been compared with data from previous calculations of the nucleophilic addition of H^– and F^– to acetylene with the formation of vinyl and fluorovinyl anions, as well as of the nucleophilic addition of H^– to methylacetylene according to and against the Markovnikov rule with the formation of the 1-propenyl and 2-propenyl anions. It has been established that the reaction with H^– is exothermic, while the reaction with F^– is endothermic. The activation energies of the reactions with F^– are lower than the activation energies of the corresponding reactions with H^–. It is shown that the reactions with H^– have a relatively early transition state, while the reactions with F^– are characterized by a later transition state.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 28, No. 1, pp. 5–11, January–February, 1992.     

Calcium Hydride Cation Dimer Catalyzed Hydrogenation of Unactivated 1-Alkenes and H2 Isotope Exchange: Competitive Ca−H−Ca Bridges and Terminal Ca−H Bonds

Recently, it was shown that the double Ca−H−Ca bridged calcium hydride cation dimer complex [LCaH₂CaL]²⁺ (macrocyclic ligand L=NNNN-tetradentate Me₄TACD) exhibited remarkable activity in catalyzing the hydrogenation of unactivated 1-alkenes as well as the H₂ isotope exchange under mild conditions, tentatively via the terminal Ca−H bond of cation monomer LCaH⁺. In this DFT mechanistic work, a novel substrate-dependent catalytic mechanism is disclosed involving cooperative Ca−H−Ca bridges for H₂ isotope exchange, competitive Ca−H−Ca bridges and terminal Ca−H bonds for anti-Markovnikov addition of unactivated 1-alkenes, and terminal Ca−H bonds for Markovnikov addition of conjugation-activated styrene. THF-coordination plays a key role in favoring the anti-Markovnikov addition while strong cation-π interactions direct the Markovnikov addition to terminal Ca−H bonds.     

Divergent Coupling of Benzocyclobutenones with Indoles via C−H and C−C Activations

Highly selective divergent coupling reactions of benzocyclobutenones and indoles, in which the chemoselectivity is controlled by catalysts, are reported herein. The substrates undergo C2(indole)–C8(benzocyclobutenone) coupling to produce benzylated indoles and benzo[b]carbazoles in the Ni- and Ru-catalyzed reactions. A completely different selectivity pattern C2(indole)–C2(benzocyclobutenone) coupling to form arylated indoles is observed in the Rh-catalyzed reaction. Preliminary mechanistic studies suggest C−H and C−C activations in the reaction pathway. Synthetic utility of this protocol is demonstrated by the selective synthesis of three different types of carbazoles from the representative products.     

Electrochemical Dehydrogenative C−H Aminomethylation of Imidazopyridines and Related Heterocycles

A facile and environmentally friendly electrochemical protocol is herein reported for the C(sp²)−C(sp³) cross dehydrogenative coupling between imidazopyridines and N,N-dimethylanilines. The broad functional group compatibility includes halogens, ester, alcohol, sulfone as well as thiophene. This methodology is also suitable for benzo[d]imidazo[2,1-b]thiazole, thiazoimidazole and tetrahydroisoquinoline, and can be scaled up to 5 mmol. Mechanistic insights are discussed.     

B−B Cleavage and Ring-Expansion of a 1,4,2,3-Diazadiborinine with N-Heterocyclic Carbenes

A 1,4,2,3-diazadiborinine derivative was found to form Lewis adducts with strong two-electron donors such as N-heterocyclic and cyclic (alkyl)(amino)carbenes. Depending on the donor, some of these Lewis pairs are thermally unstable, converting to sole B,N-embedded products upon gentle heating. The products of these reactions, which have been fully characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction, were identified as B,N-heterocycles with fused 1,5,2,4-diazadiborepine and 1,4,2-diazaborinine rings. Computational modelling of the reaction mechanism provides insight into the formation of these unique structures, suggesting that a series of B−H, C−N, and B−B bond activation steps are responsible for these “intercalation” reactions between the 1,4,2,3-diazadiborinine and NHCs.     

C−H Functionalization and Allylic Amination for Post-Polymerization Modification of Polynorbornenes

Post-polymerization modification (PPM) via direct C−H functionalization is a powerful synthetic strategy to convert polymer feed-stocks into value-added products. We found that a metal-free, Se-catalyzed allylic C−H amination provided an efficient method for PPM of polynorbornenes (PNBs) produced via ring-opening metathesis polymerization. Inherent to the mechanism of the allylic amination, PPM on PNBs preserved the alkene functional groups along the polymer backbone, while also avoiding transposition of the double bonds. Amination using a series of aryl sulfonamides led to good control over the degree of functionalization, access to a range of functionalities, and tunable thermal properties from the resulting polymers.     

Functionality-Directed Regio- and Enantio-Selective Olefinic C−H Functionalization of Aryl Alkenes

Aryl alkenes represents one of the most widely occurring structural motif in countless drugs and natural products, and direct C−H functionalization of aryl alkenes provides atom- step efficient access toward valuable analogues. Among them, group-directed selective olefinic α- and β-C−H functionalization, bearing a directing group on the aromatic ring, has attracted remarkable attentions, including alkynylation, alkenylation, amino-carbonylation, cyanation, domino cyclization and so on. These transformations proceed by endo- and exo−C−H cyclometallation and provide aryl alkene derivatives in excellent site- stereo-selectivity. Enantio-selective α- and β- olefinic C−H functionalization were also covered to synthesis axially chiral styrenes.     

On-Surface Synthesis of One-Dimensional Carbon-Based Nanostructures via C−X and C−H Activation Reactions

The past decades have witnessed the emergence of low-dimensional carbon-based nanostructures owing to their unique properties and various subsequent applications. It is of fundamental importance to explore ways to achieve atomically precise fabrication of these interesting structures. The newly developed on-surface synthesis approach provides an efficient strategy for this challenging issue, demonstrating the potential of atomically precise preparation of low-dimensional nanostructures. Up to now, the formation of various surface nanostructures, especially carbon-based ones, such as graphene nanoribbons (GNRs), kinds of organic (organometallic) chains and films, have been achieved via on-surface synthesis strategy, in which in-depth understanding of the reaction mechanism has also been explored. This review article will provide a general overview on the formation of one-dimensional carbon-based nanostructures via on-surface synthesis method. In this review, only a part of the on-surface chemical reactions (specifically, C−X (X=Cl, Br, I) and C−H activation reactions) under ultra-high vacuum conditions will be covered.     

Magnetic properties of UFe12−xSix

The homogeneity range of the system UFe_12−xSi_x with tetragonal ThMn₁₂ structure was determined to extend from x = 1 to x = 3. The Curie temperature and magnetic moment depend on the silicon content with maximum values T_c = 653 K and μ_m = 17.5 μ_B per formula unit reached at x = 2.0. The thermal expansion of UFe₁₀Si₂ was investigated by X-ray diffractometry. A volume magnetostriction of ω_s = 1% at T = 5 K was found. The hysteresis properties of powdered, sintered and melt-spun samples of UFe₁₀Si₂ were studied.     

Calorimetric investigation of interactions in the LaNi4.75Al0.25−H2 and LaNi4.8Sn0.2−H2 systems

The interaction of hydrogen with intermetalic compounds LaNi_4.75Al_0.25 and LaNi_4.8Sn_0.2 has been studied in the temperature range 308–353 K by the calorimetry titration method. The mechanism of hydrogenation was investigated. It was shown that, as the temperature increases, the initial concentration of hydrogen in the metal lattice needed for β-hydride formation decreases. It was assumed that this effect is related to the concentration of H^δ+ atoms, which “oxidize” the metallic matrix according to the scheme H^δ++M⁰→H^δ−+M⁺. The enthalpy and entropy of hydrogenation for the LaNi_4.75Al_0.25−H₂ system were calculated from thep-C-T curves and the calorimetry results. The thermodynamic parameters of the LaNi_4.8Sn_0.2−H₂ system were obtained for the first time. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1841–1844, October, 1999.