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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.

Although post-functionalization is extensively used to introduce diverse functional groups into supramolecular polymers (SPs) in solution, post-functionalization of SPs on surfaces still remains unexplored. Here we achieved the on-surface post-functionalization of two SPs derived from 5,10,15-tri-(4-pyridyl)-20-bromophenyl porphyrin (Br-TPyP) via cross-coupling reactions on Au(111). The ladder-shaped, Cu-coordinated SPs preformed from Br-TPyP were functionalized through Heck reaction with 4-vinyl-1,1'-biphenyl. In the absence of Cu, Br-TPyP formed chiral SPs as two enantiomers via self-assembly, which were functionalized via divergent cross-coupling reaction with 4-isocyano-1,1'-biphenyl (ICBP). Surprisingly, this reaction was discovered as an enantioselective on-surface reaction induced by the chirality of SPs. Mechanistic analysis and DFT calculations indicated that after debromination of Br-TPyP and the first addition of ICBP, only one attack direction of ICBP to the chiral SP intermediate is permissive in the second addition step due to the steric hindrance, which guaranteed the high enantioselectivity of the reaction.

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.

The quinoid structure, a resonance structure of benzenoid, gives rise to peculiar chemical reactivity and physical properties. A complete characterization of its geometric and electronic properties...

Template-directed polymerization is an effective approach used to afford regular 2D covalent organic frameworks (COFs), thus the regularity of the template is crucial for the quality of the resulting 2D COFs. For the Ullmann reactions on Cu(111), aryl iodides and bromides are activated at low temperature to form organometallic C-Cu-C structures, which lead to kinetic trapping and irregular organometallic networks. Therefore, the subsequent annealing step can only afford irregular 2D COFs. In this manuscript, the molecule 4,4''-dibromo-5'-(4-chlorophenyl)-1,1':3',1''-terphenyl incorporated two Br terminals and one Cl terminal has been used to demonstrate different reactivities of a C-Cl bond and a C-Br bond via the hierarchical activation of the C-Br bond and the C-Cl bond on Cu(111). At room temperature, zigzag, armchair, and ring-like organometallic chains formed due to the activation of the C-Br bond to generate a C-Cu-C structure while C-Cl remained intact, illustrating that the C-Cl bond is more stable than C-Br. Further annealing at 433 K activated the C-Cl bond to produce regular organometallic networks as the thermodynamic product. Using the simpler molecule 1,3,5-tris(4-chlorophenyl)benzene as the precursor, the self-assembly of the intact molecules was observed on Cu(111) at 300 K without activation of the C-Cl bond. After annealing at 433 K, similar thermodynamically stable organometallic networks formed directly, which were used as a template to generate regular 2D COFs upon further annealing at 510 K.

An Ir(SiNN) complex has been reported that efficiently catalyzes dehydrogenative C-H borylation, rather than hydroborylation, of terminal alkynes. Here we performed density functional theory calculations to elucidate the reaction mechanism and attempt to explain the strict chemoselectivity for dehydrogenative borylation. The calculations suggest that the chemoselectivity arises mainly from (1) interaction between Si and the metal hydride, which stabilizes the metal center during the addition of HBpin or CH3CCH; and (2) migration of the Bpin onto the amide N of the SiNN pincer ligand, which twists the pincer ligand to provide space for oxidative addition of the terminal alkyne to the Ir center.

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 CF3 radical 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.

A cascade C–H arylation/amination protocol using homoallylic primary amines as the starting materials in the presence of a palladium catalyst produces 2-aryl-1-pyrrolines with excellent regioselectivity and in good yields. Mechanistic studies indicate that this transformation proceeds via palladium-catalyzed Heck coupling, C–H amination, and tautomerization. As an unprecedented example of aryl iodide acting as an arylation reagent and a cocatalyst, the key role of aryl iodide as a cocatalyst is to generate the active bivalent aryl palladium catalyst to promote C–N formation during the C–H amination step.

Multinuclear heterometallic nanoclusters with controllable stoichiometry and structure are anticipated to possess promising catalytic, magnetic, and optical properties. Heterometallic nanoclusters with precise stoichiometry of Bi3 Cu4 and Bi7 Cu12 can be stabilized in the scaffold of two-dimensional metal-organic networks on a Cu(111) surface through on-surface metallosupramolecular self-assembly processes. The atomic structures of the nanoclusters were resolved using scanning tunneling microscopy and density functional theory calculations. The nanoclusters feature highly symmetric planar hexagonal shapes and core-shell charge modulation. The clusters are arranged as triangular lattices with a periodicity that can be tuned by choosing molecules of different size. This work shows that on-surface metallosupramolecular self-assembly creates unique possibilities for the design and synthesis of multinuclear heterometallic nanoclusters.

The heterobicyclic core retained hydroarylation of oxa/azabenzonorbornadienes with quinoline N-oxides has been achieved under rhodium catalysis, giving quinoline N-oxide substituted heterobicyclic structures with excellent regioselectivity and in good yields. As the first example of the direct introduction of quinoline N-oxides onto heterobicyclic structures, the strained heterobicyclic core was well retained in the reaction. The products could be successfully transformed into a series of useful compounds, including epibatidine analogues.

We study negative differential conductance (NDC) effects in polyporphyrin oligomers with nonlinear backbones. Using a low-temperature scanning tunneling microscope, we selectively controlled the charge transport path in single oligomer wires. We observed robust NDC when charge passed through a T-shape junction, bistable NDC when charge passed through a 90° kink and no NDC when charge passed through a 120° kink. Aided by density functional theory with nonequilibrium Green's functions simulations, we attributed this backbone-dependent NDC to bias-modulated hybridization of the electrode states with the resonant transport molecular orbital. We argue this mechanism is generic in molecular systems, which opens a new route of designing molecular NDC devices.

The reaction of aryl chloride and porphyrin macrocycles, which are merged into a single precursor, has been achieved on Cu(111). Scanning tunneling microscopy analysis of the oligomer products showed that the adjacent porphyrin moieties linked mainly by the phenyl group with the porphyrin macrocycle.

A copper-catalyzed cascade reaction of alkynols and 2-azidobenzaldehydes has been achieved, giving 6H-isochromeno[4,3-c]quinoline in yields of 40-81%. This reaction provides a novel, concise strategy for rapidly constructing compounds with fused N- and O-containing heterocycles. In contrast to previously reported reactions of alkynols in which the first step is intramolecular cycloisomerization, the first step in this novel reaction of alkynols is entropically unfavorable intermolecular addition. The resulting hemiacetal intermediate then undergoes intramolecular cyclization and aromatization to afford the product.

Using scanning tunnelling microscopy (STM), we demonstrate that Au-pyridyl coordination can be used to assemble two-dimensional coordination network structures on metal surfaces. The polymorphism of the coordination network structures can be manipulated at both the micro- and nanoscale. Using the same organic ligand, we assembled two distinct polymorphic network structures, which were assisted by threefold Au-pyridyl coordination on Ag(111) with predeposited Au atoms (α-network), and by twofold Au-pyridyl coordination on Au(111) (β-network), respectively. Specifically on the Au(111) surface, single-oriented β-network domains as large as ≈400 nm were selected by thermal annealing. We ascribe this global control strategy to distinct Au bonding modes tuned by molecule-substrate interactions. Using an STM tip, we succeeded in creating α-network domains (≈10 nm) locally within the homogeneous β-network domain areas on Au(111) in a controlled manner.

A cascade reaction of homopropargyl azides in the presence of a Cu catalyst was achieved, affording 3-(trifluoromethyl)but-3-enenitriles with good yields and excellent regioselectivity. This reaction appears to be the first direct conversion of homopropargyl azides into trifluoromethylated nitriles. Mechanistic studies indicate that the transformation proceeds by addition of a CF3 radical to the alkyne, C–C cleavage by 1,4-aryl radical migration, and nitrile formation. This protocol provides a novel strategy for transforming azides into nitriles via C–C cleavage derived from radical migration.

The porphyrin macrocyclic core features dynamic conformational transformations in free space because of its structural flexibility. Once attached to a substrate, the molecule–substrate interaction often restricts this flexibility and stabilizes the porphyrin in a specific conformation. Here using molecular dynamic and density-functional theory simulations and scanning tunneling microscopy and spectroscopy, we investigated the conformation relaxation and stabilization processes of two porphyrin derivatives (5,15-dibromophenyl-10,20-diphenylporphyrin, Br2TPP, and 5,15-diphenylporphyrin, DPP) adsorbed on Au(111) and Pb(111) surfaces. We found that Br2TPP adopts either dome or saddle conformations on Au(111) but only the saddle conformation on Pb(111), whereas DPP deforms to a ruffled conformation on Au(111). We also resolved the structural transformation pathway of Br2TPP from the free-space conformations to the surface-anchored conformations. These findings provide unprecedented insights revealing the confo...

A novel example of AgSCF3-mediated oxidative radical trifluoromethylthiolation of α,α-diaryl allylic alcohols is presented, producing various α-aryl-β-trifluoromethylthiolated carbonyl ketones via radical neophyl rearrangement under mild conditions. This protocol involves formation of C(Ar)–C(sp3) and C(sp3)–S bonds in one step and tolerates a wide range of symmetrical and nonsymmetrical α,α-diaryl allylic alcohols.

Designing metal–organic frameworks with new topologies is a long-standing quest because new topologies often accompany new properties and functions. Here we report that 1,3,5-tris[4-(pyridin-4-yl)phenyl]benzene molecules coordinate with Cu atoms to form a two-dimensional framework in which Cu adatoms form a nanometer-scale demi-regular lattice. The lattice is articulated by perfectly arranged twofold and threefold pyridyl–Cu coordination motifs in a ratio of 1 : 6 and features local dodecagonal symmetry. This structure is thermodynamically robust and emerges solely when the molecular density is at a critical value. In comparison, we present three framework structures that consist of semi-regular and regular lattices of Cu atoms self-assembled out of 1,3,5-tris[4-(pyridin-4-yl)phenyl]benzene and trispyridylbenzene molecules. Thus a family of regular, semi-regular and demi-regular lattices can be achieved by Cu–pyridyl coordination.

Radical cascade difluoroacetamidation of N-(arylsulfonyl)acrylamides with α,α-difluoro-α-(TMS)-acetamides has been achieved for the first time. This CuBr-mediated transformation is easy to perform, generates high yields and shows a good substrate scope. This cascade reaction proceeds via difluoroacetamidation, aryl migration and desulfonylation. The products can be readily transformed into synthetically useful compounds such as difluorofunctionalized esters and alcohols in excellent yields.

A novel cascade reaction of internal alkynols with 1-(2-aminophenyl)prop-2-ynols has been developed to form a new N,O-containing fused 5,5,6-tricyclic skeleton. Mechanistic studies indicate that this reaction proceeds via alkynol cycloisomerization, intermolecular substitution with 1-(2-aminophenyl)prop-2-ynols, and intermolecular addition with alkynols and consequent cyclizations. In this way, two C-C bonds, one C-O bond and one C-N bond form to give a tricyclic skeleton in a single reaction.

By using biphenyl-2-ylphosphines functionalized with a remote tertiary amino group as ligand, readily available acetylenic amides are directly converted into 2-aminofurans devoid of any electron-withdrawing and hence deactivating/stabilizing substituents. These highly electron-rich furans have rarely been prepared, let alone being applied in synthesis, due to the high reactivities and low stabilities associated with their exceedingly electron-rich nature of the furan ring. In this work, these reactive furans undergo smoothly in-situ intermolecular Diels-Alder reactions to deliver highly functionalized/substituted aniline products or intramolecular ones to furnish carbazole-4-carboxylates in mostly good to excellent yields. This work offers a general and expedient access to this class of rarely studies electron-rich furans and shall open exciting opportunities for their applications.

A highly efficient palladium-catalyzed cascade annulation of 2-vinylbenzaldehydes with indoles has been achieved to afford 6-(3-indolyl)benzo[b]carbazoles under mild conditions in good yield and with excellent regioselectivity. Mechanistic investigations reveal that the reaction proceeds via double addition of indoles, unexpected intramolecular 1,4-aryl and 1,2-hydrogen migrations, and oxidative aromatization.

Diverse self-assembled structures were obtained on Cu(111) and Ag(111) surfaces by using a simple and small 4,4′′-dichloro-1,1′:4′,1′′-terphenyl molecule. Surprisingly, a complicated supramolecular self-assembled vortex structure, composed of 15 molecules in a large unit, was realized through the collaboration of hydrogen bonding and halogen bonding.

As the first cascade C–H activation directed by a transient group, reaction of alkynols and 7-oxabenzonorbornadienes has been achieved via synergistic rhodium and scandium catalysis to afford spirocyclic dihydrobenzo[a]fluorenefurans. This transformation proceeds by a transient hemiketal group directed C–H activation, dehydrative naphthylation, and intramolecular Prins-type cyclization. Mechanistic studies and density functional theory calculations indicate that the rate-determining step is C–H bond cleavage and both the transient hemiketal group and synergistic RhIII/ScIII catalysis play key roles.

Two novel fluorescence “turn-on” cyanide probes based on the 1,3-dihydroisobenzofuran skeleton have been designed and synthesized: a terpyridyl-Cu 2+ ensemble sensed CN − in THF-H 2 O (1:1, v/v), and a dicyanovinyl-containing compound sensed CN − in CH 2 Cl 2 and THF. Titration of CN − with terpyridine-Cu 2+ complex caused a displacement reaction that turned on the fluorescence of A-Cu 2+ at 605 nm. The detection limit of A-Cu 2+ for CN − was calculated to be 3.15 × 10 −6 M. In the presence of CN − , the dicyanovinyl-bearing probe underwent a nucleophilic addition, showing 85-fold enhancement of fluorescence, with a detection limit of 5.39 × 10 −8 M. Our results demonstrate that these two strategies for designing a fluorophore skeleton based on the 1,3-dihydroisobenzofuran lead to highly selective “turn-on” probes for CN − .

A convenient palladium-catalyzed tandem reaction of aryl iodides and salicyl N-tosylhydrazones has been achieved to afford a series of compounds containing the novel spiro[benzofuran-3,2′-chromene] scaffold in moderate to good yields. This efficient catalytic reaction, which tolerates various functional groups, combines alkyne-based 5-exo-dig cyclization, palladium(II) carbene migratory insertion and intramolecular cyclization, generating three new bonds in one reaction.

A Rh(III)-catalyzed coupling/cyclization cascade reaction is described, which involves arylimidates and diazo compounds and proceeds via intermolecular C-C bond formation and subsequent intramolecular C-N bond formation. Mechanistic investigation revealed that the reaction is a two-step process: the initial Rh(III)-catalyzed coupling/cyclization proceeds very fast and the following dehydration is rather slow. The reaction provides a direct approach to isoquinolines and isoquinolin-3-ols without any oxidants.

On-surface Ullmann coupling reaction of aryl chlorides has been achieved on Cu(111), Ag(111), and Au(111), and the mechanism has been investigated on the single molecule level using scanning tunneling microscopy and density functional theory. The different reactivity of the aryl halides was utilized to design a stepwise on-surface synthesis, which affords a zigzag template and then converts to 2D porous networks.

Two tunable cascade reactions of alkynols and alkynes have been developed by combining Sc(OTf)3 and rhodium catalysis. In the absence of H2O, an endo-cycloisomerization/C-H activation cascade reaction provided 2,3-dihydronaphtho[1,2-b]furans in good to high yields. In the presence of H2O, the product of alkynol hydration underwent an addition/C-H activation cascade reaction with an alkyne, which led to the formation of 4,5-dihydro-3H-spiro[furan-2,1'-isochromene] derivatives in good yields under mild reaction conditions. Mechanistic studies of the cascade reactions indicated that the rate-determining step involves C-H bond cleavage and that the hydration of the alkynol plays a key role in switching between the two reaction pathways.

The carbon–carbon triple bond (–C≡C–) is an elementary constituent for the construction of conjugated molecular wires and carbon allotropes such as carbyne and graphyne. Here we describe a general approach to in situ synthesize –C≡C– bond on Cu(111) surface via homo-coupling of the trichloromethyl groups, enabling the fabrication of individual and arrays of poly(p-phenylene ethynylene) molecular wires. Scanning tunneling spectroscopy reveals a delocalized electronic state extending along these molecular wires, whose structure is unraveled by atomically resolved images of scanning tunneling microscopy and noncontact atomic force microscopy. Combined with density functional theory calculations, we identify the intermediates formed in the sequential dechlorination process, including surface-bound benzyl, carbene, and carbyne radicals. Our method overcomes the limitation of previous on-surface syntheses of –C≡C– incorporated systems, which require the precursors containing alkyne group; it therefore allows for a more flexible design and fabrication of molecular architectures with tailored properties., Incorporating carbon-carbon triple bonds into conjugated chains typically requires acetylenic precursors. Here, the authors synthesize poly(p-phenylene ethynylene) molecular wires on Cu(111) by directly coupling trichloromethyl-containing precursors, forming C-C triple bonds in situ

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) via dI/dV mapping 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.

By using designed biphenyl-2-ylphosphines functionalized with a remote basic groups as ligands, N-alkynyl-o-nosylamides are directly converted to (1E,3E)-1-amido-1,3-dienes with excellent diastereoselectivities under gold catalysis. With allenamides as substrates, the gold-catalyzed isomerizations are high yielding and applicable to a broad substrate scope including various nitrogen protecting groups and exhibit unprecedented (3E)-selectivities for the distal C–C double bond and good regioselectivities. Combining this gold catalysis with one-pot Diels–Alder reactions leads to rapid assembly of valuable bicyclic compounds.

Aryl homocoupling reactions via meta- and ortho-selective C–H activation have been achieved on surfaces, but the highly important para-selective C–H activation has not been reported yet. Combined with scanning tunneling microscopy, time-of-flight secondary ion mass spectrometry and density functional theory, here we describe dehydrogenative homocoupling of tetrafluorobenzene on Pd(111) via para-selective C–H activation to form perfluorinated oligo(p-phenylene)s.

The on-surface Heck reaction of aryl bromides with terminal alkene has been achieved for the first time. With palladium as the catalyst, cross-coupling of porphyrin-derived aryl bromides with terminal alkene proceeds with high selectivity on an Au(111) surface, as determined by scanning tunneling microscopy at the single molecular level. Density functional theory calculations suggest that the on-surface Heck reaction proceeds via debromination of aryl bromide, addition to the C═C bond, and elimination of hydrogen, ultimately affording the cross-coupling product.

We employed three metal-coordination structures as templates to control the Sonogashira cross-coupling reactions on a Au(111) surface catalyzed by loaded Pd. We used scanning tunnelling microscopy to resolve the products formed at the successive reaction steps and identified three vital characteristics for an efficient template: high accessibility of reaction sites, structural rigidity and thermal stability.

The efficiency of Ullmann reaction of aryl chlorides on an Au(111) surface has been substantially increased by using dosed Cu as a catalyst. The different reactivity of aryl bromides and aryl chlorides has been exploited to design a programmed, on-surface synthesis to form 2D covalent organic frameworks.

A multicomponent cascade reaction is described that provides concise access to the trifluoroethyl isoquinolines using a Rh(III)–Cu(II) bimetallic system and readily available Togni’s reagent. The system tolerates various vinyl azides and internal alkynes. Experimental results suggest that Togni’s reagent might act as a CF3 radical supplier.