Site-Selective N-Dealkylation of 1,2,3-Triazolium Salts: A Metal-Free Route to 1,5-Substituted 1,2,3-Triazoles and Related Bistriazoles

Research Advances on the Bioactivity of 1,2,3-Triazolium Salts

1,2,3-Triazolium salts have demonstrated significant potential in the fields of medicine and agriculture, exhibiting exceptional antibacterial, antifungal, anticancer, and antileishmanial properties. Moreover, these salts can be utilized as additives or components to produce nano- and fiber-based materials with antibacterial properties. In this review, we summarize several synthetic strategies to obtain 1,2,3-triazolium salts and the structures of 1,2,3-triazolium derivatives with biological activities in the domains of pharmaceuticals, pesticides, and functional materials. Additionally, the structure-activity relationship (SAR) of 1,2,3-triazolium salts with different biological activities has been analyzed. Finally, this review presents the potential applications and prospects of 1,2,3-triazolium salts in the fields of agriculture, medicine, and industrial synthesis.

Chemistry of Compounds Based on 1,2,3-Triazolylidene-Type Mesoionic Carbenes

Mesoionic carbenes (MICs) of the 1,2,3-triazolylidene type have established themselves as a popular class of compounds over the past decade. Primary reasons for this popularity are their modular synthesis and their strong donor properties. While such MICs have mostly been used in combination with transition metals, the past few years have also seen their utility together with main group elements. In this paper, we present an overview of the recent developments on this class of compounds that include, among others, (i) cationic and anionic MIC ligands, (ii) the donor/acceptor properties of these ligands with a focus on the several methods that are known for estimating such donor/acceptor properties, (iii) a detailed overview of 3d metal complexes and main group compounds with these MIC ligands, (iv) results on the redox and photophysical properties of compounds based on MIC ligands, and (v) an overview on electrocatalysis, redox-switchable catalysis, and small-molecule activation to highlight the applications of compounds based on MIC ligands in contemporary chemistry. By discussing several aspects from the synthetic, spectroscopic, and application point of view of these classes of compounds, we highlight the state of the art of compounds containing MICs and present a perspective for future research in this field.

Fluoride-Mediated Nucleophilic Aromatic Amination of Chloro-1H-1,2,3-triazolium Salts

We report a fluoride-mediated nucleophilic aromatic amination of chloro-1H-1,2,3-triazolium salts with aliphatic amines. The reaction proceeded under mild reaction conditions to provide amino-1,2,3-triazolium salts with various functional groups, which can be utilized for further transformations. Moreover, it was found that an amino-1,2,3-triazolium salt was transformed via deprotonation into the N-heterocyclic imine (NHI), which exhibited the excellent catalytic activity for the cyanosilylation of acetophenone with trimethylsilyl cyanide.

Uncommon carbene-to-azole ligand rearrangement of N-heterocyclic carbenes in a ruthenium system

The study of non-innocent behavior of NHCs (NHCs = N-heterocyclic carbenes) has great implications for NHC-involved catalysis. Herein, we report a new type of NHC-to-azole rearrangement, during which process the carbene backbone and the substituent are both non-innocent. To the best of our knowledge, this work also presents the first example of NHC-to-azole rearrangements for aryl-substituted NHCs.

Employing Aryl-Linked Bis-mesoionic Carbenes as a Pincer-Type Platform to Access Ambient-Stable Palladium(IV) Complexes

The study of palladium(IV) species has great implications for Pd^II /Pd^IV -mediated catalysis. However, most of the Pd^IV complexes rapidly decompose under ambient conditions, which makes the isolation, characterization and further reactivity study very challenging. The reported ancillary ligand platforms to stabilize Pd^IV species are dominated by chelating N-donors such as bipyridines. In this work, we present two Pd^IV complexes with scarcely used C-donors as the supporting platform. The anionic aryl donor and MIC (MIC=mesoionic carbene) are combined in a [CC'C]-type pincer framework to access a series of ambient-stable Pd^IV tris(halido) complexes. Their synthesis, solid-state structures, stability, and reactivity are presented. To the best of our knowledge, the work presented herein reports the first isolated Pd^IV -MIC as well as the first Pd^IV carbene-based aryl pincer.

Synthesis of aminyl biradicals by base-induced Csp3-Csp3 coupling of cationic azo dyes

The synthesis of the industrially important polymer parylene is achieved by polymerization of p-quinodimethane (p-QDM). The polymerization is thought to proceed via a biradical p-QDM dimer, but isolation or characterization of such a biradical has remained elusive. Here, we describe the synthesis of an aza-analogue of this p-QDM dimer. The biradical is formed by base-induced dimerization of an azoimidazolium dye. Due to the presence of sterically shielded aminyl radicals instead of terminal H2Ċ groups, the stability of this dimer is sufficient for analyses by ESR spectroscopy and X-ray crystallography. A similar Csp3-Csp3 coupling was observed for an azotriazolium dye, suggesting that base-induced C-C coupling reactions can be realized for different types of azo dyes.

Self-assembled orthoester cryptands: orthoester scope, post-functionalization, kinetic locking and tunable degradation kinetics

Dynamic adaptability and biodegradability are key features of functional, 21st century host-guest systems. We have recently discovered a class of tripodal supramolecular hosts, in which two orthoesters act as constitutionally dynamic bridgeheads. Having previously demonstrated the adaptive nature of these hosts, we now report the synthesis and characterization - including eight solid state structures - of a diverse set of orthoester cages, which provides evidence for the broad scope of this new host class. With the same set of compounds, we demonstrated that the rates of orthoester exchange and hydrolysis can be tuned over a remarkably wide range, from rapid hydrolysis at pH 8 to nearly inert at pH 1, and that the Taft parameter of the orthoester substituent allows an adequate prediction of the reaction kinetics. Moreover, the synthesis of an alkyne-capped cryptand enabled the post-functionalization of orthoester cryptands by Sonogashira and CuAAC "click" reactions. The methylation of the resulting triazole furnished a cryptate that was kinetically inert towards orthoester exchange and hydrolysis at pH > 1, which is equivalent to the "turnoff" of constitutionally dynamic imines by means of reduction. These findings indicate that orthoester cages may be more broadly useful than anticipated, e.g. as drug delivery agents with precisely tunable biodegradability or, thanks to the kinetic locking strategy, as ion sensors.

A mini review of the synthesis of poly-1,2,3-triazole-based functional materials

Most recent advances of the synthesis of poly-1,2,3-triazole-based functional materials.