Copper-Catalyzed Coupling of (E)-Bromostilbene with Phenols/Azole: ESI-MS Detection of Intermediates by Using an Ionically-Tagged Ligand

Fifty Shades of Phenanthroline: Synthesis Strategies to Functionalize 1,10-Phenanthroline in All Positions

1,10-Phenanthroline (phen) is one of the most popular ligands ever used in coordination chemistry due to its strong affinity for a wide range of metals with various oxidation states. Its polyaromatic structure provides robustness and rigidity, leading to intriguing features in numerous fields (luminescent coordination scaffolds, catalysis, supramolecular chemistry, sensors, theranostics, etc.). Importantly, phen offers eight distinct positions for functional groups to be attached, showcasing remarkable versatility for such a simple ligand. As a result, phen has become a landmark molecule for coordination chemists, serving as a must-use ligand and a versatile platform for designing polyfunctional arrays. The extensive use of substituted phenanthroline ligands with different metal ions has resulted in a diverse array of complexes tailored for numerous applications. For instance, these complexes have been utilized as sensitizers in dye-sensitized solar cells, as luminescent probes modified with antibodies for biomaterials, and in the creation of elegant supramolecular architectures like rotaxanes and catenanes, exemplified by Sauvage's Nobel Prize-winning work in 2016. In summary, phen has found applications in almost every facet of chemistry. An intriguing aspect of phen is the specific reactivity of each pair of carbon atoms ([2,9], [3,8], [4,7], and [5,6]), enabling the functionalization of each pair with different groups and leading to polyfunctional arrays. Furthermore, it is possible to differentiate each position in these pairs, resulting in non-symmetrical systems with tremendous versatility. In this Review, the authors aim to compile and categorize existing synthetic strategies for the stepwise polyfunctionalization of phen in various positions. This comprehensive toolbox will aid coordination chemists in designing virtually any polyfunctional ligand. The survey will encompass seminal work from the 1950s to the present day. The scope of the Review will be limited to 1,10-phenanthroline, excluding ligands with more intracyclic heteroatoms or fused aromatic cycles. Overall, the primary goal of this Review is to highlight both old and recent synthetic strategies that find applicability in the mentioned applications. By doing so, the authors hope to establish a first reference for phenanthroline synthesis, covering all possible positions on the backbone, and hope to inspire all concerned chemists to devise new strategies that have not yet been explored.

Selectfluor-induced C(sp2)–O coupling reaction of N-substituted anilines with hydroxylamine derivatives

We developed a novel metal-free method for the construction of C(sp²)–O bonds via oxidative cross-coupling reactions between various N-substituted anilines and hydroxylamine derivatives just using commercially available Selectfluor as an oxidant.

Oxidative annulations triggered by a simple Lewis acid: facile synthesis of benzofurans

The first example of Lewis acid promoted efficient one-pot synthesis of benzofurans is presented.

Ligand free copper(I)-catalyzed synthesis of diaryl ether with Cs2CO3 via a free radical path

Complexes [Cu(I)(2,4-dimethylphenoxy)2](-) (A) and [Cu(II)(2,4-dimethylphenoxy)2(p-tolyl)](-) (B) were observed by in situ electrospray ionization mass spectrometry (ESI-MS) analysis of the ligand free copper(I)-catalyzed C-O coupling reaction using Cs2CO3 under the catalytic reaction conditions indicating that they could be intermediates in the reaction. The radical scavenger cumene retarded the reaction. Catalytic cycles involving a free radical path are proposed based on these observations.

Synthesis of fluorovinyl aryl ethers by a three-component reaction of gem-difluoroalkenes with arylboronic acids and oxygen

An efficient three-component reaction for the synthesis of fluorovinyl aryl ethers from gem-difluoroalkenes, arylboronic acids and oxygen is described.

Palladium metal nanoparticles stabilized by ionophilic ligands in ionic liquids: synthesis and application in hydrogenation reactions

The selectivity of the hydrogenation of 1,3-cyclohexadiene and 2-pentyne by Pd nanoparticles in an ionic liquid can be modulated by the addition of N- or P-containing ionophilic ligands.

Possible intermediates of Cu(phen)-catalyzed C-O cross-coupling of phenol with an aryl bromide by in situ ESI-MS and EPR studies

The C-O coupling reaction between 2,4-dimethylphenol and 4-bromotoluene catalyzed by the CuI/K2CO3/phen system can be inhibited by the radical scavenger cumene. Complexes [Cu(i)(phen)(1-(2,4-dimethylphenoxy)-4-methylbenzene)](+) (denoted as A), {H[Cu(i)(phen)(2,4-dimethylphenoxy)]}(+) and [Cu(i)(2,4-dimethylphenoxy)2](-) (denoted as B) were observed by in situ electrospray ionization mass spectrometry (ESI-MS) analysis of the copper(i)-catalyzed C-O coupling reaction under the catalytic reaction conditions indicating that they could be intermediates in the reaction. The in situ EPR study of the reaction solution detected the Cu(ii) species with a fitted g value of 2.188. A catalytic cycle with a single electron transfer (SET) step was proposed based on these observations.

Charge-tagged ligands: useful tools for immobilising complexes and detecting reaction species during catalysis

A critical overview is presented on the use of charged tagged ligands (CTLs) as immobilising agents in organometallic catalysis and as probes for studying mechanisms through electrospray ionisation mass spectrometry (ESI-MS) based on the most recent literature.

In recent years, charge-tagged ligands (CTLs) have become valuable tools in organometallic catalysis. Insertion of an ionic side chain into the molecular skeleton of a known ligand has become a useful protocol for anchoring ligands, and consequently catalysts, in polar and ionic liquid phases. In addition, the insertion of a cationic moiety into a ligand is a powerful tool that can be used to detect reaction intermediates in organometallic catalysis through electrospray ionisation mass spectrometry (ESI-MS) experiments. The insertion of an ionic tag ensures the charge in the intermediates independently of the ESI-MS. For this reason, these ligands have been used as ionic probes in mechanistic studies for several catalytic reactions. Here, we summarise selected examples on the use of CTLs as immobilising agents in organometallic catalysis and as probes for studying mechanisms through ESI-MS.

Stereoselective synthesis of (E)-3,3-diaryl and (E)-3-aryl-3-aryloxy allylamines and allylalcohols from trans-cinnamyl chloride and alcohol

Syntheses of (E)-3,3-diaryl and (E)-3-aryl-3-aryloxy allylamines and allylalcohols based on bromination/dehydrobromination sequences followed by Suzuki cross-coupling or Ullmann vinylation were achieved.