Cu-catalysed arylation reactions devoted to the formation of C–C and C–heteroatom bonds (Ullmann-type couplings) have acquired great importance in the last decade. This review discusses the history and development of coupling reactions between aryl halides and various classes of nucleophiles, focusing mostly on the different mechanisms proposed through the years. Selected mechanistic investigations are treated more in depth than others. For example, evidence in favour or against radical mechanisms is discussed. Cu(I) and Cu(III) complexes involved in the Ullmann reaction and N/O selectivity in aminoalcohol arylation are discussed. A separate section has been dedicated to the synthesis of heterocyclic rings through intramolecular couplings. Finally, recent developments in green chemistry for these reactions, such as reactions in aqueous media and heterogeneous catalysis, have also been reviewed.

https://pubs.rsc.org/en/content/getauthorversionpdf/C3CS60289C

Copper catalysed Ullmann type chemistry: From mechanistic aspects to modern development

Exploiting the reactivity of one functional group within a molecule to generate a reaction at a different position is an ongoing challenge in organic synthesis. Effective remote functionalization protocols have the potential to provide access to almost any derivatives but are difficult to achieve. The difficulty is more pronounced for acyclic systems where flexible alkyl chains are present between the initiating functional group and the desired reactive centres. In this Review, we discuss the concept of remote functionalization of alkenes using metal complexes, leading to a selective reaction at a position distal to the initial double bond. We aim to show the vast opportunity provided by this growing field through selected and representative examples. Our aim is to demonstrate that using a double bond as a chemical handle, metal-assisted long-distance activation could be used as a powerful synthetic strategy.

Remote functionalization through alkene isomerization

Metal organic frameworks (MOFs) are porous crystalline solids whose structure is formed by metal ions or clusters of a few metal ions held in place by bi- or multipodal organic linkers. In some cases, the metal nodes in MOFs have exchangeable coordination positions that allow them to participate as active sites promoting organic reactions. There is much current interest in exploiting the advantages that MOFs offer as catalysts, including a large surface area, high metal content, flexibility in the design of the active sites in the framework, together with the easy synthesis of these materials. In the present review we describe the use of MOFs as catalysts to promote cross-coupling reactions involving organometallic reaction intermediates and catalysis by Lewis acid sites. These types of reactions are of large synthetic utility due to the high yields achieved, mild conditions and compatibility with other functional groups. The content includes C–C bond forming reactions, such as Suzuki–Miyaura, Mizoroki–Heck, Sonogashira, Stille and Ullmann, but also C–O and C–N cross-couplings. The final section summarizes our views on future developments and targets in these types of reactions. The core of the review is references that have appeared in 2010 or after, which give an idea of the novelty and current interest in this area.

Metal-organic frameworks catalyzed C-C and C-heteroatom coupling reactions.

The synthesis of substituted benzimidazoles, 2-aminobenzimidazoles, 2-aminobenzothiazoles, and benzoxazoles is described via intramolecular cyclization of o-bromoaryl derivatives using copper(II) oxide nanoparticles in DMSO under air. The procedure is experimentally simple, general, efficient, and free from addition of external chelating ligands. It is a heterogeneous process and the copper(II) oxide nanoparticles can be recovered and recycled without loss of activity.

Ligand-Free Copper-Catalyzed Synthesis of Substituted Benzimidazoles, 2-Aminobenzimidazoles, 2-Aminobenzothiazoles, and Benzoxazoles

The direct synthesis of amides from alcohols and amines is achieved using gold nanoparticles immobilized on DNA as a heterogeneous catalyst.

Highly efficient amide synthesis from alcohols and amines by virtue of a water-soluble gold/DNA catalyst.

A metal-free catalytic system for the oxidation of benzylic methylenes and primary amines under solvent-free conditions

Nano‐CuO‐Catalyzed Ullmann Coupling of Phenols with Aryl Halides under Ligand‐Free Conditions

A novel palladium catalyzed isomerization of alkenes has been found, where an ortho-phenol hydroxyl group has a pronounced influence on the isomerization.

Palladium catalyzed isomerization of alkenes: a pronounced influence of an o-phenol hydroxyl group

Asymmetric surfaces endow Janus bismuth oxyhalides with enhanced electronic and catalytic properties for the hydrogen evolution reaction.

Abstract Semiconducting graphene nanoribbons are promising materials for nanoelectronics but are held back by synthesis challenges. Here we report that molecular-scale carbon seeds can be exploited to initiate the chemical vapor deposition (CVD) synthesis of graphene to generate one-dimensional graphene nanoribbons narrower than 5 nm when coupled with growth phenomena that selectively extend seeds along a single direction. This concept is demonstrated by subliming graphene-like polycyclic aromatic hydrocarbon molecules onto a Ge(001) catalyst surface and then anisotropically evolving size-controlled nanoribbons from the seeds along $$\left\langle 110\right\rangle$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:mn>110</mml:mn> </mml:mrow> </mml:mfenced> </mml:math> of Ge(001) via CH 4 CVD. Armchair nanoribbons with mean normalized standard deviation as small as 11% (3 times smaller than nanoribbons nucleated without seeds), aspect ratio as large as 30, and width as narrow as 2.6 nm (tunable via CH 4 exposure time) are realized. Two populations of nanoribbons are compared in field-effect transistors (FETs), with off-current differing by 150 times because of the nanoribbons’ different widths. 

/pdf/graphene-nanoribbons-initiated-from-molecularly-derived-94mpd67t.pdf

Xiaoqi Zheng

Papers

A metal-free catalytic system for the oxidation of benzylic methylenes and primary amines under solvent-free conditions

Nano‐CuO‐Catalyzed Ullmann Coupling of Phenols with Aryl Halides under Ligand‐Free Conditions

Palladium catalyzed isomerization of alkenes: a pronounced influence of an o-phenol hydroxyl group

Asymmetric surfaces endow Janus bismuth oxyhalides with enhanced electronic and catalytic properties for the hydrogen evolution reaction.

Graphene nanoribbons initiated from molecularly derived seeds