Synthesis, photophysical characterisation, quantum-chemical study and in vitro antiproliferative activity of cyclometalated Ir(III) complexes based on 3,5-dimethyl-1-phenyl-1H-pyrazole and N,N-donor ligands

In this paper, we present the synthesis of four new complexes: the dimeric precursor [Ir(dmppz)2(μ-Cl)]2 (1) (Hdmppz - 3,5-dimethyl-1-phenyl-1H-pyrazole) and heteroleptic bis-cyclometalated complexes: [Ir(dmppz)2(Py2CO)]PF6·½CH2Cl2 (2), [Ir(dmppz)2(H2biim)]PF6·H2O (3), and [Ir(dmppz)2(PyBIm)]PF6 (4), with auxiliary N,N-donor ligands: 2-di(pyridyl)ketone (Py2CO), 2,2'-biimidazole (H2biim) and 2-(2'-pyridyl)benzimidazole (PyBIm). In the obtained complexes, SC-X-ray analysis revealed that Ir(III) has an octahedral coordination sphere with chromophores of the type {IrN2C2Cl2} (1) or {IrN4C2} (2-4). The complexes obtained, which have been fully characterised by physicochemical methods (CHN, TG, FTIR, UV-Vis, PL and 1H, 13C, 15N NMR), were used to continue our studies on the factors influencing the cytotoxic properties of potential chemotherapeutic agents (in vitro). To this end, the following studies are presented: (i) comparative analysis of the effects on the biological properties of N,N-donor ligands and C,N-donor ligands in the studied complexes, (ii) studies of the interactions of the compounds with the selected molecular target: DNA and BSA (UV-Vis, CD and PL methods), (iii) and the reactivity towards redox molecules: GSH, NADH (UV-Vis and/or ESI-MS methods), (iv) cytotoxic activity (IC50) of potential chemotherapeutics against MCF-7, K-562 and CCRF-CEM cell lines.

Imidazopyridine Family: Versatile and Promising Heterocyclic Skeletons for Different Applications

In recent years, there has been increasing attention focused on various products belonging to the imidazopyridine family; this class of heterocyclic compounds shows unique chemical structure, versatile optical properties, and diverse biological attributes. The broad family of imidazopyridines encompasses different heterocycles, each with its own specific properties and distinct characteristics, making all of them promising for various application fields. In general, this useful category of aromatic heterocycles holds significant promise across various research domains, spanning from material science to pharmaceuticals. The various cores belonging to the imidazopyridine family exhibit unique properties, such as serving as emitters in imaging, ligands for transition metals, showing reversible electrochemical properties, and demonstrating biological activity. Recently, numerous noteworthy advancements have emerged in different technological fields, including optoelectronic devices, sensors, energy conversion, medical applications, and shining emitters for imaging and microscopy. This review intends to provide a state-of-the-art overview of this framework from 1955 to the present day, unveiling different aspects of various applications. This extensive literature survey may guide chemists and researchers in the quest for novel imidazopyridine compounds with enhanced properties and efficiency in different uses.

Experimental and theoretical studies of pH-responsive iridium(III) complexes of azole and N-heterocyclic carbene ligands

A series of nine luminescent iridium(III) complexes with pH-responsive imidazole and benzimidazole ligands have been prepared and characterized. The first series of complexes were of the form [Ir(ppy)2(N^N)]+ or [Ir(ppy)2(C^N)]+ (where ppy is 2-phenylpyridine and N^N is 2-(2-pyridyl)imidazole or 2-(2-pyridyl)benzimidazole and C^N represents a pyridyl-triazolylidene-based N-heterocyclic carbene ligand). For these complexes, the benzimidazole group was either unsubstituted or substituted with electron-withdrawing (Cl) or electron-donating (Me) groups. The second series of complexes were of the form [Ir(phbim)2(N^N)]+ or [Ir(phbim)2(C^N)]+ (where phbim is 2-phenylbenzimidazole and N^N is either 2,2'-bipyridine or 1,10-phenanthroline and C^N is either a pyridyl-imidazolylidene or pyridyl-triazolylidene N-heterocyclic carbene ligand). UV-visible and photoluminescence pH titration studies showed that changing the protonation state of these complexes results in significant changes in the photoluminescence emission properties. The pKa values of prepared complexes were estimated from the spectroscopic pH titration data and these values show that the nature of the pH-sensitive ligands (either main or ancillary ligands) resulted in a significant capacity to modulate the pKa values for these compounds with values ranging from 5.19-11.22. Theoretical investigations into the nature of the electronic transitions for the different protonation states of compounds were performed and the results were consistent with the experimental results.

Dipyridylmethane Ethers as Ligands for Luminescent Ir Complexes

This work reports two new cationic heteroleptic cyclometalated iridium complexes, containing ether derivatives of di(pyridin-2-yl)methanol. The new ligands are based on dipyridin-2-ylmethane and are designed to obtain ether-based intermediates with extended electronic conjugation by insertion of π system such as phenyl, allyl and ethynyl. Different synthetic strategies were employed to introduce these units, as molecular wires, between the dipyridin-2-ylmethane chelating portion and the terminal N-containing functional group, such as amine and carbamide. The corresponding complexes show luminescence in the blue region of the spectrum, lifetimes between 0.6 and 2.1 μs, high quantum yield and good electrochemical behavior. The computational description (DFT) of the electronic structure highlights the key role of the conjugated π systems on optical and electrochemical properties of the final products.

Phosphorescent cationic iridium(iii) complexes bearing a nonconjugated six-membered chelating ancillary ligand: a strategy for tuning the emission towards the blue

Blue and blue-green-emitting cationic Ir(iii) complexes bearing a nonconjugated N^N ligand have been studied.

Electrochemical CO2 Reduction at Glassy Carbon Electrodes Functionalized by MnI and ReI Organometallic Complexes

The catalytic activities towards electrochemical CO₂ reduction of two new rhenium and manganese complexes, namely fac-Mn(apbpy)(CO)₃ Br (1) and fac-Re(apbpy)(CO)₃ Cl (2) (apbpy=4-(4-aminophenyl)-2,2'-bipyridine), in both homogeneous and heterogeneous phases are compared. A glassy carbon electrode (GCE) surface has been functionalized with complexes 1 and 2 by two approaches: a) direct electrochemical oxidation of the amino group with formation of C-N bonds, and b) electrochemical reduction of the corresponding diazonium salts with formation of C-C bonds. The chemically modified GCEs show efficient conversion of CO₂ into CO, with turnover numbers (TONs) about 60 times higher than those of the corresponding catalysts in homogeneous solutions, and in a much shorter time.