Palladium‐Catalyzed C−H Alkynylation of Unactivated Alkenes

Palladium‐catalyzed regio‐ and diastereoselective C?H functionalization with bromoalkynes and electronically unbiased olefins is reported. The picolinamide directing group enables the formation of putative 5 and 6‐exo‐metallacycles as intermediates to afford monoalkynylated products in up to 91 % yield in a stereospecific fashion. The systematic study reveals that substrates with a wide range of substituents on the olefin and bromoalkyne coupling partners are tolerated. Chemoselective transformations were demonstrated for the obtained amides, olefins, and alkynes.     

On‐Surface Domino Reactions: Glaser Coupling and Dehydrogenative Coupling of a Biscarboxylic Acid To Form Polymeric Bisacylperoxides

Herein we report the on‐surface oxidative homocoupling of 6,6′‐(1,4‐buta‐1,3‐diynyl)bis(2‐naphthoic acid) (BDNA) via bisacylperoxide formation on different Au substrates. By using this unprecedented dehydrogenative polymerization of a biscarboxylic acid, linear poly‐BDNA with a chain length of over 100 nm was prepared. It is shown that the monomer BDNA can be prepared in situ at the surface via on‐surface Glaser coupling of 6‐ethynyl‐2‐naphthoic acid (ENA). Under the Glaser coupling conditions, BDNA directly undergoes polymerization to give the polymeric peroxide (poly‐BDNA) representing a first example of an on‐surface domino reaction. It is shown that the reaction outcome varies as a function of surface topography (Au(111) or Au(100)) and also of the surface coverage, to give branched polymers, linear polymers, or 2D metal–organic networks.     

Direct Formation of C−C Triple‐Bonded Structural Motifs by On‐Surface Dehalogenative Homocouplings of Tribromomethyl‐Substituted Arenes

On‐surface synthesis shows significant potential in constructing novel nanostructures/nanomaterials, which has been intensely studied in recent years. The formation of acetylenic scaffolds provides an important route to the fabrication of emerging carbon nanostructures, including carbyne, graphyne, and graphdiyne, which feature chemically vulnerable sp‐hybridized carbon atoms. Herein, we designed and synthesized a tribromomethyl‐substituted compound. By using a combination of high‐resolution scanning tunneling microscopy, non‐contact atomic force microscopy, and density functional theory calculations, we demonstrated that it is feasible to convert these compounds directly into C?C triple‐bonded structural motifs by on‐surface dehalogenative homocoupling reactions. Concurrently, sp³‐hybridized carbon atoms are converted into sp‐hybridized ones, that is, an alkyl group is transformed into an alkynyl moiety. Moreover, we achieved the formation of dimer structures, one‐dimensional molecular wires, and two‐dimensional molecular networks on Au(111) surfaces, which should inspire further studies towards two‐dimensional graphyne structures.     

Z‐Selective (Cross‐)Dimerization of Terminal Alkynes Catalyzed by an Iron Complex

Efficient iron‐catalyzed homocoupling of terminal alkynes and cross‐dimerization of aryl acetylenes with trimethylsilylacetylene is reported. The complex [Fe(H)(BH₄)(iPr‐PNP)] ( 1 ) catalyzed the (cross‐)dimerization of alkynes at room temperature, with no need for a base or other additives, to give the corresponding dimerized products with Z selectivity in excellent yields (79–99 %).     

Nickel‐Catalyzed Carboxylation of Benzylic C−N Bonds with CO2

A user‐friendly Ni‐catalyzed reductive carboxylation of benzylic C?N bonds with CO₂ is described. This procedure outperforms state‐of‐the‐art techniques for the carboxylation of benzyl electrophiles by avoiding commonly observed parasitic pathways, such as homodimerization or β‐hydride elimination, thus leading to new knowledge in cross‐electrophile reactions.     

Graphene‐Oxide‐Catalyzed Direct CH−CH‐Type Cross‐Coupling: The Intrinsic Catalytic Activities of Zigzag Edges

The development of graphene oxide (GO)‐based materials for C?C cross‐coupling represents a significant advance in carbocatalysis. Although GO has been used widely in various catalytic reactions, the scope of reactions reported is quite narrow, and the relationships between the type of functional groups present and the specific activity of the GO are not well understood. Herein, we explore CH?CH‐type cross‐coupling of xanthenes with arenes using GO as real carbocatalysts, and not as stoichiometric reactants. Mechanistic studies involving molecular analogues, as well as trapped intermediates, were carried out to probe the active sites, which were traced to quinone‐type functionalities as well as the zigzag edges in GO materials. GO‐catalyzed cross‐dehydrogenative coupling is operationally simple, shows reusability over multiple cycles, can be conducted in air, and exhibits good functional group tolerance.     

表面合成异质原子掺杂的石墨烯纳米带

超高真空环境下,通过自下而上的方法原子级精确合成石墨烯纳米带是打开石墨烯带隙的重要方法。合理地设计带有异质原子(如硼、氮、氧等)的前驱体分子可以合成异质原子掺杂的石墨烯纳米带。掺杂的异质原子可以显著地调制石墨烯纳米带的电学、磁学等物理化学性质,并且调控的效果与异质原子的种类、位置、密度等密切相关。本文综述了近些年来利用分子束外延方法,在表面上合成异质原子掺杂的石墨烯纳米带的研究进展,同时对掺杂石墨烯纳米带的应用前景进行了展望。     

Pd(0)‐Catalyzed Dearomative Diarylation of Indoles

We have developed a protocol for a Pd(0)‐catalyzed dearomative syn 1,2‐diarylation of indoles using readily available boroxines (dehydrated boronic acids) as coupling partners. This reaction proceeds efficiently using PtBu₃ as the ligand to divergently access to fused indolines while minimizing the extent of direct Suzuki coupling. The scope of the reaction is remarkably broad and all products are obtained as single diastereomers in moderate to excellent yields. We have also compiled data which parallels the steric and electronic properties of both substrate and boroxine with the propensity to undergo the desired dearomative process over direct Suzuki coupling.     

Chemoselective On‐surface Homocoupling of Terminal Alkynes Catalyzed by Exogenous Cupric Ions

The on‐surface coupling reactions of terminal alkynes catalyzed by exogenous cupric ions on chemically inert highly oriented pyrolytic graphite (HOPG) surface have been investigated by scanning tunnelling microscopy. In the presence of exogenous cupric ions, diyne‐linked nanostructures generated via homocoupling of terminal alkynes are the exclusive products, whereas no coupling reaction occurs for the terminal alkynes on the surface in the absence of the cupric ions, suggesting that exogenous cupric ions are efficient to catalyze the highly chemoselective on‐surface reaction of terminal alkynes. The HOPG surface displays a template effect to the growth and alignment of the products on the surface. As a result, 2D arrays of diyne‐linked zigzag polymers and 2D diyne‐linked porous polymers are fabricated from ditopic monomer 3,6‐diethynylcarbazole and tritopic monomer 1,3,5‐tris‐(4‐ethynylphenyl) benzene, respectively. This synthetic strategy combining the high selectivity of cupric ion catalyst as well as the template effect of on‐surface synthesis approach could be a general strategy to fabricate diyne‐linked nanostructures and nanomaterials on solid surfaces.     

Recent Progress in Application of Graphene Supported Metal Nanoparticles in C−C and C−X Coupling Reactions

The carbon‐carbon and carbon‐heteroatom bonds catalytic formation is among the most significant reactions in organic synthesis which extensively applied for synthesis of natural products, heterocycles, dendrimers, biologically active molecules and useful compounds. This review provides the latest advances in the preparation of graphene supported metal nanoparticles and their application in the catalytic formation of both carbon‐carbon (C−C) and carbon‐heteroatom (C−X) bonds including the Suzuki, Heck, Hiyama, Ullmann, Buchwald and Sonogashira coupling reactions. Numerous examples are given concerning the use of these catalysts in C−C and C−X coupling reactions along with the reliable and simple preparation methods of these catalysts, their characterization and catalytic properties and also the recycling possibilities.     

Synthesis of Strained γ‐Lactams by Palladium(0)‐Catalyzed C(sp3)−H Alkenylation and Application to Alkaloid Synthesis

A variety of strained α‐alkylidene‐γ‐lactams were synthesized by palladium(0)‐catalyzed intramolecular C(sp³)?H alkenylation from easily accessible acyclic and monocyclic bromoalkene precursors. These lactams are valuable intermediates for accessing various classes of mono‐ and bicylic alkaloids containing a pyrrolidine ring, as illustrated with the synthesis of an advanced model of the marine natural product plakoridine A and of the indolizidine alkaloid δ‐coniceine.     

Nickel‐Catalyzed Amide Bond Formation from Methyl Esters

Despite being one of the most important and frequently run chemical reactions, the synthesis of amide bonds is accomplished primarily by wasteful methods that proceed by stoichiometric activation of one of the starting materials. We report a nickel‐catalyzed procedure that can enable diverse amides to be synthesized from abundant methyl ester starting materials, producing only volatile alcohol as a stoichiometric waste product. In contrast to acid‐ and base‐mediated amidations, the reaction is proposed to proceed by a neutral cross coupling‐type mechanism, opening up new opportunities for direct, efficient, chemoselective synthesis.     

Transition Metal Catalyzed Coupling Reactions under C−H Activation

C−C coupling by transition metal catalyzed C−H activation has developed into a diverse area of research. The applicable catalysts are manifold, and the variety of products obtained range from basic chemicals to pharmaceuticals and building blocks for carbon networks. One reaction, in which several C−C bonds are formed under C−H activation of a methyl group, is the conversion of ortho-iodoanisole according to Equation (1).     

Enantioselective Synthesis of N–C Axially Chiral Compounds by Cu‐Catalyzed Atroposelective Aryl Amination

N?C axially chiral compounds have emerged recently as appealing motifs for drug design. However, the enantioselective synthesis of such molecules is still poorly developed and surprisingly no metal‐catalyzed atroposelective N‐arylations have been described. Herein, we disclose an unprecedented Cu‐catalyzed atroposelective N?C coupling that proceeds at room temperature. Such mild reaction conditions, which are a crucial parameter for atropostability of the newly generated products, are operative thanks to the use of hypervalent iodine reagents as a highly reactive coupling partners. A large panel of the N?C axially chiral compounds was afforded with very high enantioselectivity (up to >99 % ee) and good yields (up to 76 %). Post‐modifications of thus accessed atropisomeric compounds allows further expansion of the diversity of these appealing compounds.     

On-Surface Synthesis and Spectroscopic Characterization of Laterally Extended Chevron Graphene Nanoribbons

We report the on-surface synthesis and spectroscopic study of laterally extended chevron graphene nanoribbons (GNRs) and compare them with the established chevron GNRs, emphasizing the consistency of bandgap reduction of semiconducting GNRs with increased width. The laterally extended chevron GNRs grown on Au(111) exhibit a bandgap of about 2.2 eV, which is considerably smaller than the values reported for chevron GNRs in similar studies.     

Lewis Acid Assisted Nickel‐Catalyzed Cross‐Coupling of Aryl Methyl Ethers by C−O Bond‐Cleaving Alkylation: Prevention of Undesired β‐Hydride Elimination

In the presence of trialkylaluminum reagents, diverse aryl methyl ethers can be transformed into valuable products by C?O bond‐cleaving alkylation, for the first time without the limiting β‐hydride elimination. This new nickel‐catalyzed dealkoxylative alkylation method enables powerful orthogonal synthetic strategies for the transformation of a variety of naturally occurring and easily accessible anisole derivatives. The directing and/or activating properties of aromatic methoxy groups are utilized first, before they are replaced by alkyl chains in a subsequent coupling process.     

Ligand‐Enabled Nickel‐Catalyzed Redox‐Relay Migratory Hydroarylation of Alkenes with Arylborons

A redox‐relay migratory hydroarylation of isomeric mixtures of olefins with arylboronic acids catalyzed by nickel complexes bearing diamine ligands is described. A range of structurally diverse 1,1‐diarylalkanes, including those containing a 1,1‐diarylated quaternary carbon, were obtained in excellent yields and with high regioselectivity. Preliminary experimental evidence supports the proposed non‐dissociated chainwalking of aryl‐nickel(II)‐hydride species along the alkyl chain of alkenes before selective reductive elimination at a benzylic position. A catalyst loading as low as 0.5 mol % proved to be sufficient in large‐scale synthesis while retaining high reactivity, highlighting the practical value of this transformation.