Search

Quantum spins, also known as spin operators that preserve SU(2) symmetry, lack a specific orientation in space and are hypothesized to display unique interactions with superconductivity. However, spin–orbit coupling and crystal field typically cause a significant magnetic anisotropy in d/f shell spins on surfaces. Here, we fabricate atomically precise S= 1/2 magnetic nanographenes on Pb(111) through engineering sublattice imbalance in the graphene honeycomb lattice. Through tuning the magnetic exchange strength between the unpaired spin and Cooper pairs, a quantum phase transition from the singlet to the doublet state has been observed, consistent with the quantum spin models. From our calculations, the particle-hole asymmetry is induced by the Coulomb scattering potential and gives a transition point about kBTk≈ 1.6Δ. Our work demonstrates that delocalized π electron magnetism hosts highly tunable magnetic bound states, which can be further developed to study the Majorana bound states and other rich quantum phases of low-dimensional quantum spins on superconductors.

Alkaline ionomers used in anion exchange membrane water electrolyzers (AEMWEs) require fast mass transport to maximize the activity of the catalytic reaction at the three-phase boundary. Taking advantage of the high free volume of polymers of intrinsic microporosity (PIMs), herein we propose a new strategy to apply ionized PIMs in the preparation of high-performance alkaline ionomers. A series of novel intrinsic microporous poly(phenyl-alkane) alkaline ionomers were synthesized by acid-catalyzed Friedel–Crafts polycondensation of electron-rich single-benzene/multi-benzene derivatives and trifluoromethyl/cyanide-substituted benzaldehydes. By adjusting the structure of aromatic monomers and aldehydes and the proportion of comonomers, the structures of the ionomer skeletons were systematically regulated. By evaluating the microporosities, ion transport properties, and device properties, we found that introducing a twisted spirobisindane unit and a trifluoromethyl substituent to the poly(phenyl-alkane) skeleton promoted the formation of more micropore structures. Increased microporosity is beneficial for the construction of efficient and stable mass transfer channels, facilitating improved AEMWE performance (1685 mA cm–2at 1.8 V with a circulating 1 M NaOH solution at 80 °C) and excellent durability (>180 h at a high current density of 1000 mA cm–2). This work provides insights into the structure–property relationships of intrinsic microporous poly(phenyl-alkane) alkaline ionomers and demonstrates that ionic intrinsic microporous polymers are very promising candidates for the preparation of high-performance alkaline ionomers for AEMWEs.

Two-dimensional (2D) crystal-to-crystal transition is an important method in crystal engineering because of its ability to directly create diverse crystal materials from one crystal. However, steering a 2D single-layer crystal-to-crystal transition on surfaces with high chemo- and stereoselectivity under ultra-high vacuum conditions is a great challenge because the transition is a complex dynamic process. Here, we report a highly chemoselective 2D crystal transition from radialene to cumulene with retention of stereoselectivity on Ag(111) via retro-[2 + 1] cycloaddition of three-membered carbon rings and directly visualize the transition process involving a stepwise epitaxial growth mechanism by the combination of scanning tunneling microscopy and non-contact atomic force microscopy. Using progression annealing, we found that isocyanides on Ag(111) at a low annealing temperature underwent sequential [1 + 1 + 1] cycloaddition and enantioselective molecular recognition based on C–H···Cl hydrogen bonding interactions to form 2D triaza[3]radialene crystals. In contrast, a higher annealing temperature induced the transformation of triaza[3]radialenes to generate trans-diaza[3]cumulenes, which were further assembled into 2D cumulene-based crystals through twofold N–Ag–N coordination and C–H···Cl hydrogen bonding interactions. By combining the observed distinct transient intermediates and density functional theory calculations, we demonstrate that the retro-[2 + 1] cycloaddition reaction proceeds via the ring opening of a three-membered carbon ring, sequential dechlorination/hydrogen passivation, and deisocyanation. Our findings provide new insights into the growth mechanism and dynamics of 2D crystals and have implications for controllable crystal engineering.

The emergence of quantum magnetism in nanographenes provides ample opportunities to fabricate purely organic devices for spintronics and quantum information. Although heteroatom doping is a viable way to engineer the electronic properties of nanographenes, the synthesis of doped nanographenes with collective quantum magnetism remains elusive. Here, a set of nitrogen-doped nanographenes (N-NGs) with atomic precision are fabricated on Au(111) through a combination of imidazole [2+2+2]-cyclotrimerization and cyclodehydrogenation reactions. High-resolution scanning probe microscopy measurements reveal the presence of collective quantum magnetism for nanographenes with three radicals, with spectroscopic features which cannot be captured by mean-field density functional theory calculations but can be well reproduced by Heisenberg spin model calculations. In addition, the mechanism of magnetic exchange interaction of N-NGs has been revealed and compared with their counterparts with pure hydrocarbons. Our findings demonstrate the bottom-up synthesis of atomically precise N-NGs which can be utilized to fabricate low-dimensional extended graphene nanostructures for realizing ordered quantum phases.

We report a novel rhodium-catalyzed rearrangement involving N-substituted 2-thiopyridones and diazoesters. This reaction proceeds through the rhodium-catalyzed formation of sulfur ylides, followed by a direct C–N bond cleavage to achieve N-to-C 1,4-pyridyl migration. The protocol can be used to construct various thiopyridines possessing tetrasubstituted carbon stereocenters in moderate to excellent yields, which expands the transformation pattern of sulfur ylide intermediates in rearrangement reactions.

Molecular adsorption conformations and arrangement configurations on surfaces are important structural aspects of surface stereochemistry, but their roles in steering the structures of metal–organic networks (MONs) remain vague and unexplored. In this study, we constructed MONs by the coordination self-assembly of isocyanides on Cu(111) and Ag(111) surfaces and demonstrated that the MON structures can be steered by surface stereochemistry, including the adsorption conformations of the isocyanide molecules and the arrangement configurations of the coordination nodes and subunits. The coordination self-assembly of 1,4-phenylene diisocyanobenzene afforded a honeycomb MON consisting of 3-fold (isocyano)3–Cu motifs on a Cu(111) surface. In contrast, geometrically different chevron-shaped 1,3-phenylene diisocyanobenzene (m-DICB) failed to generate a MON, which is ascribable to its standing conformation on the Cu(111) surface. However, m-DICB was adsorbed in a flat conformation on a Ag(111) surface, which has a larger lattice constant than a Cu(111) surface, and smoothly underwent coordination self-assembly to form a MON consisting of (isocyano)3–Ag motifs. Interestingly, only C3–Ag nodes with heterotactic configurations could grow into larger subunits; those subunits with heterotactic configurations further grew into Sierpiński triangle fractals (up to fourth order), while subunits with homotactic configurations afforded a triangular MON.

The direct C–H activation without directing groups can realize the para-selectivity, which is a powerful and concise approach for functionalization of arenes. Utilizing the strategy, a C5-olefination of methyleneindolinones has been successfully developed by palladium-catalyzed direct C–H activation, which provides an expeditious access to 5-vinylindolin-2-ones with high regioselectivity. The protocol is distinguished by a mild reaction system avoiding ligand and high temperature. The kinetic isotope experiments indicate that the C–H bond cleavage is the rate-limiting step.

Supramolecular coordination self-assembly on solid surfaces provides an effective route to form two-dimensional (2D) metal–organic frameworks (MOFs). In such processes, surface–adsorbate interaction plays a key role in determining the MOFs’ structural and chemical properties. Here, we conduct a systematic study of Cu-HAT (HAT = 1,4,5,8,9,12-hexaazatriphenylene) 2D conjugated MOFs (c-MOFs) self-assembled on Cu(111), Au(111), Ag(111), and MoS2substrates. Using scanning tunneling microscopy and density functional theory calculations, we found that the as-formed Cu3HAT2c-MOFs on the four substrates exhibit distinctive structural features including lattice constant and molecular conformation. The structural variations can be attributed to the differentiated substrate effects on the 2D c-MOFs, including adsorption energy, lattice commensurability, and surface reactivity. Specifically, the framework grown on MoS2is nearly identical to its free-standing counterpart. This suggests that the 2D van der Waals (vdW) materials are good candidate substrates for building intrinsic 2D MOFs, which hold promise for next-generation electronic devices.

One of the most appealing topics in the study of metal–organic networks is the growth mechanism. However, its study is still considered a significant challenge. Herein, using scanning tunneling microscopy, the growth mechanisms of metal–alkynyl networks on Ag(111) and Au(111) surfaces were investigated at the atomic scale. During the reaction of 1,3,5-tris(chloroethynyl)benzene on Ag(111), honeycomb Ag-alkynyl networks formed at 393 K, and only short chain intermediates were observed. By contrast, the same precursor formed honeycomb Au–alkynyl networks on Au(111) at 503 K. Progression annealing led to a stepwise evolution process, in which the sequential activation of three Cl-alkynyl bonds led to the formation of dimers, zigzag chains, and novel chiral networks as the intermediates. Moreover, density functional theory calculations indicate that chlorine atoms are crucial in assisting the breakage of metal-alkynyl bonds to form Cl-metal-alkynyl, which guarantees the reversibility of the break/formation equilibration as the key to forming regular large-scale organometallic networks.

Vinylethylene carbonates have been extensively used to trigger [3 + n] or [5 + n] cycloaddition via the formation of η3-allylic intermediates, while the important [4 + n] cycloaddition has not been explored yet. Here, we report a new strategy to convert vinylethylene carbonates into 4-(trimethylsilyl)but-2-en-1-ols, which can readily undergo [4 + 2] cycloaddition by in situ formation of 1,3-dienes. This novel reaction involves [PdII]-catalyzed decarboxylative silylation, [FeIII]-catalyzed vinylogous Peterson elimination, and subsequent [4 + 2] cycloaddition to afford a multisubstituted cyclohexa-1,4-diene skeleton.

A novel copper-catalyzed radical cyanotrifluoromethylation has been achieved through a multicomponent reaction of isocyanides, Togni’s reagent, and trimethylsilyl cyanides, affording trifluoroacetimidoyl nitriles in good yields. This reaction demonstrates a unique feature of merging two valuable functional groups—trifluoromethyl (CF3) and cyan (CN)—onto the same C atom. The transformation proceeds by the initial addition of the CF3radical to isocyanide and the subsequent intermolecular C–CN formation. The products can be successfully transformed to a series of CF3-containing amines and imines that may serve in the synthesis of valuable pharmaceuticals and agrochemicals.

We have characterized the local electronic structure of a porphyrin-containing single-layer covalent organic framework (COF) exhibiting a square lattice. The COF monolayer was obtained by the deposition of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMA) and 5,10,15,20-tetrakis(4-aminophenyl) porphyrin (TAPP) onto a Au(111) surface in ultrahigh vacuum followed by annealing to facilitate Schiff-base condensations between monomers. Scanning tunneling spectroscopy (STS) experiments conducted on isolated TAPP precursor molecules and the covalently linked COF networks yield similar transport (HOMO–LUMO) gaps of 1.85 ± 0.05 eV and 1.98 ± 0.04 eV, respectively. The COF orbital energy alignment, however, undergoes a significant downward shift compared to isolated TAPP molecules due to the electron-withdrawing nature of the imine bond formed during COF synthesis. Direct imaging of the COF local density of states (LDOS) viadI/dVmapping reveals that the COF HOMO and LUMO states are localized mainly on the porphyrin cores and that the HOMO displays reduced symmetry. DFT calculations reproduce the imine-induced negative shift in orbital energies and reveal that the origin of the reduced COF wave function symmetry is a saddle-like structure adopted by the porphyrin macrocycle due to its interactions with the Au(111) substrate.

We used porous supramolecular structures as templates to make two-dimensional (2D) superlattices of Bi nanoclusters on a Au(111) surface. First, we applied on-surface self-assembly to prepare 2D porous supramolecular structures containing well-ordered nanopores. Then, we deposited Bi atoms on the surface. The Bi atoms were confined in the supramolecular pores and formed nanoclusters of a critical size that is defined by the pore size. These nanoclusters were arranged as a 2D superlattice dictated by the structure of the supramolecular templates. The nanocluster size and superlattice periodicity can be adjusted by appropriately designing the supramolecular structures. We further studied the formation mechanism of the nanoclusters. We found that Bi atoms could diffuse across the pore boundaries at room temperature and nucleated as clusters inside the pores. The clusters grew until they reached the critical size and became stable. We used kinetic Monte Carlo simulations to reproduce the experimental results and quantified the interpore diffusion barrier to be 0.65 eV.

We have studied the self-assembly of a series of multicomponent cyclic supramolecular polygons on a Au(111) surface using scanning tunneling microscopy and kinetic Monte Carlo simulations. Our results indicate that while closed polygons or cages efficiently self-assemble in three dimensions at appropriate temperatures and concentrations, chain structures are formed predominantly and the yield of cyclic polygon structures is very low in two dimensions independent of temperature and concentration. This substantial shift in the ring–chain equilibrium can be attributed to subtle competition between kinetic and thermodynamic controls. Simulations suggest that on a surface, where the translational and rotational freedom of the molecules are restricted and intramolecular bond flipping is hindered, the low-energy reaction pathways that are essential for the formation of cyclic structures are blocked. In addition, microscopy images suggest that surface defects provide kinetic traps that further reduce the yield of cyclic structures. Our findings reveal the striking differences between the on-surface self-assembly and solution self-assembly of discrete supramolecular systems.

On-surface covalent polymerization is a powerful tool for the atomically precise synthesis of polymeric materials with interesting properties and functions. Although on-surface covalent polymerization has been achieved with several coupling reactions, ring-opening coupling on surfaces is still rarely used. Herein, we report an unprecedented ring-opening coupling reaction of epoxides on Ag(110) and Ag(111) surfaces and investigate the coupling process using scanning tunneling microscopy, noncontact atomic force microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. The Ag(110) surface promoted the ring-opening coupling reaction of 1,4-di(oxiran-2-yl)benzene by acting as a template to direct the formation of a zigzag 1,2-ethylene-bridged parylene polyradical oriented in the [11̅0] crystallographic direction. In contrast, the ring-opening coupling reaction of the same precursor on the Ag(111) surface formed irregular polymers. Moreover, the ring-opening coupling reaction of 2-([1,1′-biphenyl]-4-yl)oxirane on the Ag(110) surface was proved to involve ring-opening of the ethylene oxide group, C–C coupling, and deoxygenation, whereas C–C coupling was favored along the [11̅0] orientation.

A series of novel imidazolium-based cationic organic polymers (COPs) with various ionic capacities (ICs) and porosities were synthesized by adjusting the structure of the building units and applied to the adsorption of organic dyes from aqueous solutions. The charge-incorporated polymer without pores was almost incapable of adsorbing dyes. Among polymers with similar porosities, COPs with higher IC values exhibited higher adsorption capacities, and the polymer with the largest IC but only a surface area of 74.2 m2g–1exhibited the best adsorption performance toward Acid Orange 7 (559.4 mg g–1, 21 times that of the uncharged polymer). The results demonstrated the synergistic effect between IC and intrinsic porosity: high porosity was necessary for adsorption, whereas electrostatic interactions between charges and dyes dominate removal efficiency; increasing the charge content is more effective than increasing the surface area in this polymer system. This work provides in-depth insight into the organic-dye adsorption process and a path toward the rational molecular design of high-performance COPs.

A dicationic dichloro‐bipyridine‐ruthenium complex shows very high catalytic activity in redox isomerization of allylic alcohols but a relatively low one in transfer hydrogenation of ketones; surprisingly, the analogous dimethyl‐bipyridine‐ruthenium complex shows reverse catalytic activities in the two reactions.

The new ruthenium complex [Ru(N3P)(OAc)][BPh4] (4), in which N3P is the N,P mixed tetradentate ligand N,N‐bis[(pyridin‐2‐yl)methyl]‐[2‐(diphenylphosphino)phenyl]methanamine was synthesized. The complex was found to be catalytically active for the endocycloisomerization of alkynols. The catalytic reactions can be used to synthesize five‐, six‐, and seven‐membered endo‐cyclic enol ethers in good to excellent yields. A catalytic cycle involving a vinylidene intermediate was proposed for the catalytic reactions. Treatment of complex 4with PhCCH and H2O gave the alkyl complex [Ru(CH2Ph)(CO)(N3P)][BPh4] (30), which supports the assumption that the catalytic reactions involve addition of a hydroxyl group to the CC bond of vinylidene ligands.

The perchlorate salt of the dicationic bipy–ruthenium complex cis‐[Ru(6,6′‐Cl2bipy)2(H2O)2]2+effectively catalyzes addition of β‐diketones to secondary alcohols and styrenes to yield the α‐alkylated β‐diketones. In a catalytic addition reaction of acetylacetone to 1‐phenylethanol, the κ2‐acetylacetonate complex [Ru(6,6′‐Cl2bipy)2(κ2‐acac)]ClO4was isolated after the catalysis; this complex is readily synthesized by reacting cis‐[Ru(6,6′‐Cl2bipy)2(H2O)2](ClO4)2with acetylacetone. [Ru(6,6′‐Cl2bipy)2(κ2‐acac)]ClO4is unreactive toward 1‐phenylethanol in the presence of HClO4; it also fails to catalyze the addition of acetylacetone to 1‐phenylethanol. On the basis of these observations, it is proposed and confirmed by independent experiments that the catalytic addition of β‐diketones to the secondary alcohols is in fact catalyzed by the Brønsted acid HClO4, which is generated by the reaction of cis‐[Ru(6,6′‐Cl2bipy)2(H2O)2](ClO4)2with the β‐diketone.

Easily accessible N-(p-tolylsulfonyl)-1,2-diphenylethylenediamine-(TsDPEN-)derived organic–inorganic hybrid ligands were prepared and applied to the heterogeneous asymmetric transfer hydrogenation in traditional HCO2H/NEt3 and in water with HCO2Na as the hydrogen source and sodium dodecyl sulfate (SDS) as the phase-transfer catalyst. The reactions demonstrated high catalytic activities and excellent enantioselectivities for most aromatic ketones and the imine tested, with results similar to those in homogeneous catalysis.In particular, this heterogeneous catalyst can be readily recovered and used in multiple consecutive catalytic runs with the high enantioselectivity maintained both in HCO2H/NEt3 and in water. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

We report a step-economic strategy for the direct synthesis of bridged polycyclic skeletons by merging oxidative C–H annulation and cascade cycloaddition. In the protocol, spiro[cyclopentane-1,3′-indoline]-2,4-dien-2′-ones were first synthesized by oxidative C–H annulation of ethylideneoxindoles with alkynes. Subsequent cascade [4 + 2] cycloaddition with dienophiles gave the bridged bicyclo[2.2.1]quinolin-2(1H)-ones and enabled the one-pot construction of two quaternary carbon centers and three C–C bonds. Mechanistic investigations of the latter suggest a cascade ring-opening, 1,5-sigmatropic rearrangement, and [4 + 2] cycloaddition process.

Ladder phenylenes (LPs) composed of alternating fused benzene and cyclobutadiene rings have been synthesized in solution with a maximum length no longer than five units. Longer polymeric LPs have not been obtained so far because of their poor stability and insolubility. Here, we report the synthesis of linear LP chains on the Au(111) surface via dehalogenative [2+2] cycloaddition, in which the steric hindrance of the methyl groups in the 1,2,4,5-tetrabromo-3,6-dimethylbenzene precursor improves the chemoselectivity as well as the orientation orderliness. By combining scanning tunneling microscopy and noncontact atomic force microscopy, we determined the atomic structure and the electronic properties of the LP chains on the metallic substrate and NaCl/Au(111). The tunneling spectroscopy measurements revealed the charged state of chains on the NaCl layer, and this finding is supported by density functional theory calculations, which predict an indirect bandgap and antiferromagnetism in the polymeric LP chains.

A highly efficient heterogeneous asymmetric transfer hydrogenation of ketones in water was developed for the first time, which exhibited excellent enantioselectivities, distinct acceleration effect and remarkably high recyclabilities.

A highly efficient heterogeneous asymmetric transfer hydrogenation of ketones in water was developed for the first time, which exhibited excellent enantioselectivities, distinct acceleration effect and remarkably high recyclabilities.

Two versions including triflic acid adsorbed on silica gel are used for the title reaction and generally similar yields are produced.

A Ru(II)—dichlorobipyridine complex (Ia) efficiently catalyzes the redox isomerization of terminal and internal allylic alcohols to give the corresponding ketones, e.g. (III), (V) or (VII), in high to excellent conversion.

It is found that HClO4and silica gel supported HClO4efficiently promote the addition of β‐dicarbonyl compounds to secondary alcohols and alkenes.

Five‐, six‐, and seven‐membered endocyclic enol ethers are prepared in good to excellent yield by the title reaction.

Twenty‐two examples for the title reaction are presented, affording the corresponding products in moderate to excellent yields under solvent‐free conditions or in nitromethane.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.