Beijing National Laboratory of Molecular Sciences (BNLMS) and Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry and Green Chemistry Center, Peking University, 202 Chengfu Road, 098#, Beijing 100871, China State Key Laboratory of Organometallic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 200060, China

Transition-Metal-Free Coupling Reactions

In the last 12 years the field of hyperbranched polymers has been well established with a large variety of synthetic approaches and fundamental studies on structure and properties of these unique materials. However, new developments involving hyperbranched materials appeared recently, for example, different synthetic strategies, new reaction mechanisms, formation of more complex architectures, a deeper understanding of the branched structure and their kinetic development, and intensive studies on the material properties and possible applications. This demonstrates the high versatility and the possibilities that are still involved in hyperbranched polymers and render it one of the most active fields in polymer science with a very promising future. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2505–2525, 2000

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1099-0518%2820000715%2938%3A14%3C2505%3A%3AAID-POLA10%3E3.0.CO%3B2-8

New developments in hyperbranched polymers

The use of diazonium salts for aryl radical generation and C-H arylation processes has been known since 1896 when Pschorr first used the reaction for intramolecular cyclizations. Meerwein developed it further in the early 1900s into a general arylation method. However, this reaction could not compete with the transition-metal-mediated formation of C(sp2) -C(sp2) bonds. The replacement of the copper catalyst with iron and titanium compounds improved the situation, but the use of photocatalysis to induce the one-electron reduction and activation of the diazonium salts is even more advantageous. The first photocatalyzed Pschorr cyclization was published in 1984, and just last year a series of papers described applications of photocatalytic Meerwein arylations leading to aryl-alkene coupling products. In this Minireview we summarize the origins of this reaction and its scope and applications.

http://www.chtf.stuba.sk/~szolcsanyi/education/files/Organicka%20chemia%20II/Prednaska%202_Aminy_Reakcie/Doplnkove%20studijne%20materialy/Diazonium%20salts/The%20Photocatalyzed%20Meerwein%20Arylation.pdf

The Photocatalyzed Meerwein Arylation: Classic Reaction of Aryl Diazonium Salts in a New Light

Azobenzenes are ubiquitous motifs very important in many areas of science. Azo compounds display crucial properties for important applications, mainly for the chemical industry. Because of their discovery, the main application of aromatic azo compounds has been their use as dyes. These compounds are excellent candidates to function as molecular switches because of their efficient cis–transisomerization in the presence of appropriate radiation. The classical methods for the synthesis of azo compounds are the azo coupling reaction (coupling of diazonium salts with activated aromatic compounds), the Mills reaction (reaction between aromatic nitroso derivatives and anilines) and the Wallach reaction (transformation of azoxybenzenes into 4-hydroxy substituted azoderivatives in acid media). More recently, other preparative methods have been reported. This critical review covers the various synthetic methods reported on azo compounds with special emphasis on the more recent ones and their mechanistic aspects (170 references).

http://www.chtf.stuba.sk/~szolcsanyi/education/files/Organicka%20chemia%20II/Prednaska%202_Aminy_Reakcie/Doplnkove%20studijne%20materialy/Azobenzenes/Synthesis%20of%20azobenzenes%20-%20the%20coloured%20pieces%20of%20molecular%20materials.pdf

Synthesis of azobenzenes: the coloured pieces of molecular materials

Control over molecular motion represents an important objective in modern chemistry. Aromatic azobenzenes are excellent candidates as molecular switches since they can exist in two forms, namely the cis (Z) and trans (E) isomers, which can interconvert both photochemically and thermally. This transformation induces a molecular movement and a significant geometric change, therefore the azobenzene unit is an excellent candidate to build dynamic molecular devices. We describe selected examples of systems containing an azobenzene moiety and their motions and geometrical changes caused by external stimuli.

/pdf/control-over-molecular-motion-using-the-cis-trans-2k1rnm11bu.pdf

Control over molecular motion using the cis–trans photoisomerization of the azo group

On heating, aromatic diazonium salts eliminate nitrogen by two fundamentally different mechanistic pathways, i.e. heterolysis and homolysis. Among these pathways a series of variants are known, giving rise to a whole variety of mechanisms. This article considers the effect of specific solvation, apparently characteristic of diazonium ions, by various solvents (fluorinated alcohols, methanol, water, dimethyl sulfoxide, pyridine, and hexamethylphosphoric triamide) on the mechanism. Apart from the donor properties of the solvent, the oxidation potential and the presence of additives play a major role in determining what reaction type will predominate.

Nitrogen as Leaving Group: Dediazoniations of Aromatic Diazonium Ions

The substituted benzylideneanilines 2–7 and the respective 3H-indoles 9–14 have been synthesized A comparison of their electronic absorption spectra shows it is likely that 4-nitrobenzylidene-4′,-dimethylaminoaniline (6) has a planar conformation

On the Planarisation of Benzylideneaniline

Azo coupling reactions structures and mechanisms

Reaktivstoffe sind farbige Verbindungen, die im Laufe des Farbeprozesses kovalente Bindungen mit dem gefarbten Material (Textilfasern, Kunststoffe) eingehen Diese Farbstoffe wurden erstaunlich spat entwickelt Die wesentlichen Arbeiten auf diesem Gebiet stammen erst aus den letzten zwei Jahrzehnten Uberraschenderweise lassen sich Reaktivfarbstoffe im wasrigen Farbebad auch mit Cellulose umsetzen Typen, Technologie und Reaktionsweise der Reaktivfarbstoffe werden zusammenfassend beschrieben Auf Grund von kinetischen Versuchen (Saure-, Basen- und Autokatalyse, Isotopeneffekte) wird der Mechanismus nucleophiler Substitutionen aromatischer Heterocyclen vom Typ des Cyanurchlorids eingehend besprochen

Chemismus der Reaktivfarbstoffe

Dediazoniation of arenediazonium ions in homogeneous solution. 10. Solvent effects on the reactions of benzene- and 2,4,6-trimethylbenzenediazonium ion. Evidence for two intermediates

Heinrich Zollinger

Papers

Nitrogen as Leaving Group: Dediazoniations of Aromatic Diazonium Ions

On the Planarisation of Benzylideneaniline

Azo coupling reactions structures and mechanisms

Chemismus der Reaktivfarbstoffe

Dediazoniation of arenediazonium ions in homogeneous solution. 10. Solvent effects on the reactions of benzene- and 2,4,6-trimethylbenzenediazonium ion. Evidence for two intermediates