An Efficient Synthesis of Bis-1,3-(3′-aryl-N-heterocycl-1′-yl)arenes as CCC-NHC Pincer Ligand Precursors

Diaryliodonium(III) Salts in One-Pot Double Functionalization of C–IIII and ortho C–H Bonds

Since the 1950s, diaryliodonium(III) salts have been demonstrated to participate in various arylation reactions, forming aryl–heteroatom and aryl–carbon bonds. Incorporating the arylation step into sequential transformations would provide access to...

Electrosynthesis of 1,2,4-Triazolium Tetrafluoroborates

The synthesis of 1,2,4-triazolium tetrafluoroborates under electrochemical conditions is reported. The reaction is performed with stoichiometric amounts of HBF₄, which converts starting materials to their corresponding cationic forms due to protonation. As a result, sufficient conductivity is gained in MeOH, CD₃OD, and EtOH, and no additional supporting electrolyte is required. Agrochemical fungicide, (±)-triticonazole (1), is transformed in this manner into 2a, an O-methylated potential intermediate involved in the metabolism of 1, in 42% yield on a gram scale.

Bis-tridentate IrIII Phosphors Bearing Two Fused Five-Six-Membered Metallacycles: A Strategy to Improved Photostability of Blue Emitters

Iridium complexes bearing chelating cyclometalates are popular choices as dopant emitters in the fabrication of organic light-emitting diodes (OLEDs). In this contribution, we report a series of blue-emitting, bis-tridentate Ir^III complexes bearing chelates with two fused five-six-membered metallacycles, which are in sharp contrast to the traditional designs of tridentate chelates that form the alternative, fused five-five metallacycles. Five Ir^III complexes, Px-21-23, Cz-4, and Cz-5, have been synthesized that contain a coordinated dicarbene pincer chelate incorporating a methylene spacer and a dianionic chromophoric chelate possessing either a phenoxy or carbazolyl appendage to tune the coordination arrangement. All these tridentate chelates afford peripheral ligand-metal-ligand bite angles of 166-170°, which are larger than the typical bite angle of 153-155° observed for their five-five-coordinated tridentate counterparts, thereby leading to reduced geometrical distortion in the octahedral frameworks. Photophysical measurements and TD-DFT studies verified the inherent transition characteristics that give rise to high emission efficiency, and photodegradation experiments confirmed the improved stability in comparison with the benchmark fac-[Ir(ppy)₃ ] in degassed toluene at room temperature. Phosphorescent OLED devices were also fabricated, among which the carbazolyl-functionalized emitter Cz-5 exhibited the best performance among all the studied bis-tridentate phosphors, showing a maximum external quantum efficiency (EQE_max ) of 18.7 % and CIE_x,y coordinates of (0.145, 0.218), with a slightly reduced EQE of 13.7 % at 100 cd m^-2 due to efficiency roll-off.

Catalytic Preparation of 1-Aryl-Substituted 1,2,4-Triazolium Salts

1,4-Diaryl- and 1-aryl-4-alkyl-substituted 1,2,4-triazolium salts are convenient air-stable precursors to carbenes used both as organocatalysts or as ligands for transition metal complexes. Traditionally, they are prepared via a multistep synthetic pathway with the low-yielding formation of the triazolium ring occurring in the last step. We have developed an alternative two-step synthesis involving the conversion of a primary amine or aniline derivative to the corresponding 4-substituted triazole followed by a copper-catalyzed arylation with diaryliodonium salts. This transition metal-catalyzed arylation can be carried out under mild conditions in acetonitrile and is tolerant toward both water and oxygen. Additionally, the high functional group tolerance of the protocol described here gives easy access to triazolium salts containing heterocyclic substituents or sulfides.

An efficient synthesis of triazolium ion based NHC precursors using diaryliodonium salts and their photophysical properties

Copper-catalysed N-arylation of fused triazoles using diaryliodonium salts as an aryl source is described. This scalable protocol displayed good compatibility towards diverse sensitive functional groups like ester, alkyl and nitro groups and halogens (F, Cl, Br). The synthetic usefulness of the prepared triazolium salts was proved by preparing α-hydroxyketone through benzoin condensation. Photophysical studies of these compounds showed promising Stokes-shifted fluorescence emission in aqueous medium, so this molecular framework could be a proficient probe for biological applications.

Additive-Free Pd-Catalysed C-2 Arylation of Tryptophan Derivatives with Diaryliodonium Salts

An efficient, mild and Pd-catalysed C-2 arylation of Fmoc-L-tryptophan with diaryliodonium salts has been developed, giving easy access to C-2 arylated tryptophan derivatives. This protocol tolerates a variety of functional groups and proceeds smoothly in high yields without any additives. In addition, the chemoseletive C–H arylation with unsymmetrical salts is described.

Phosphorescent Pt(ii) complexes bearing a monoanionic C^N^N luminophore and tunable ancillary ligands

A new monoanionic pincer luminophore is presented, yielding phosphorescent Pt(ii) complexes bearing a neutral 1,2,3-triazole ring introduced via click chemistry. The overall charge, intermolecular interactions and excited state properties can be manipulated and controlled.

The search for formal electrostatic effects on molecular conformation and crystal packing: crystal structure of 2,2''-disubstituted (H versus PPh2) 1,1'-(1,2-phenylene)bis(3-methyl-1H-imidazol-3-ium) bis(trifluoromethanesulfonate)

Electrostatic interactions between localized integral charges make the stability and structure of highly charged small and rigid organics intriguing. Can σ/π-electron delocalization compensate reduced conformational freedom by lowering the repulsion between identical charges? The crystal structure of the title salt, C14H16N4(2+)·2CF3SO3(-), (2), is described and compared with that of the 2,2''-bis(diphenylphosphanyl) derivative, (4). The conformations of the dications and their interactions with neighbouring trifluoromethanesulfonate anions are first analyzed from the standpoint of formal electrostatic effects. Neither cation exhibits any geometrical strain induced by the intrinsic repulsion between the positive charges. In contrast, the relative orientation of the imidazolium rings [i.e. anti for (2) and syn for (4)] is controlled by different configurations of the interactions with the closest trifluoromethanesulfonate anions. The long-range arrangement is also found to be specific: beyond the formal electrostatic packing, C-H...O and C-H...F contacts have no definite `hydrogen-bond' character but allow the delineation of layers, which are either pleated or flat in the packing of (2) or (4), respectively.

Monoanionic bis(carbene) pincer complexes featuring cobalt(I–III) oxidation states

The synthesis and characterization of a series of cobalt complexes featuring a pincer bis(carbene) ligand of the meta-phenylene-bridged bis-N-heterocyclic carbene (^ArCCC, Ar = 2,6-diispropylphenyl or mesityl) are reported.

Arylation with Diaryliodonium Salts

This chapter focuses on recent developments in metal-free and metal-catalyzed arylations with diaryliodonium salts (diaryl-λ3-iodanes). Synthetic routes to diaryliodonium salts are briefly described, and chemoselectivity trends with unsymmetric iodonium salts are discussed.

A Convenient N-Arylation Route for Electron-Deficient Pyridines: The Case of π-Extended Electrochromic Phosphaviologens

A simple and representative procedure for the synthesis of N,N'-diarylated phosphaviologens directly from both electron-rich and electron-poor diaryliodonium salts and 2,7-diazadibenzophosphole oxide is reported. The latter are electron-deficient congeners of the widely utilized N,N'-disubstituted 4,4'-bipyridinium cations, also known as viologens, that proved to be inaccessible by the classical two-step route. The single-step preparation method for phosphaviologens described herein could be extended to genuine viologens but reached its limit when sterically demanding diaryliodonium salts were used. The studied phosphaviologens feature a significantly lowered reduction threshold as compared to all other (phospha)viologens known to date due to the combination of an extended π-system with an electron deficient phosphole core. In addition, a considerably smaller HOMO-LUMO gap was observed due to efficient π-delocalization across the phosphaviologen core, as well as the N-aryl substituents, which was corroborated by quantum chemical calculations. Detailed characterizations of the singly reduced radical species by EPR spectroscopy and DFT calculations verified delocalization of the radical over the extended π-system. Finally, to gain deeper insight into the suitability of the new compounds as electroactive and electrochromic materials, multicolored proof-of-concept electrochomic devices were manufactured.

ONO pincer type Pd(ii) complexes: synthesis, crystal structure and catalytic activity towards C-2 arylation of quinoline scaffolds

Four new palladium(ii) complexes featuring ONO pincer type hydrazone ligands were synthesized and characterized by spectroscopic and single-crystal XRD analysis. Utility of these complexes to catalyze C–C bond formation in quinoline scaffolds were assessed.