“Click” Synthesis of Heteroleptic Tris-Cyclometalated Iridium(III) Complexes: Cu(I) Triazolide Intermediates as Transmetalating Reagents

Modulatory Role of Pantropic Cell Signaling Pathways in the Antimigratory and Antiproliferative Action of Triazole Chelated Iridium(III) Complexes in Cervical Cancer Cells

In the current study, the antimigratory and antiproliferative effect of three substituted triazole-chelated iridium(III) complexes Ir-TRN, Ir-TRH, and Ir-TRF were studied with special emphasis on modulation of P53 activity, a cell cycle regulator. ERK2/MAPK, another crucial cell signaling pathway protein, was also shown to play a crucial role in cell migration and proliferation. The complexes increase the ROS generation within the cell, further supporting apoptotic induction by exerting cellular oxidative stress. These metal complexes also affect ER stress by altering ERp29, an ER-resident chaperone, further inducing the process of apoptosis. The iridium(III) complexes restrict cervical cancer cell migration and proliferation by exerting pronounced effects as P53 activators and downregulation of ERK2/MAPK activity in cervical cancer cells. The underpinning mechanism of P53 and ERK2/MAPK activity in cervical cancer cells in the presence of iridium(III) complexes was studied in detail in this study, which paves the way for developing promising avenues for cancer therapeutics.

Click-derived multifunctional metal complexes for diverse applications

The Click reaction that involves Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) serves as the most potent and highly dependable tool for the development of many complex architectures. It has paved the way for the synthesis of numerous drug molecules with enhanced synthetic flexibility, reliability, specificity and modularity. It is all about bringing two different molecular entities together to achieve the required molecular properties. The utilization of Click chemistry has been well demonstrated in organic synthesis, particularly in reactions that involve biocompatible precursors. In pharmaceutical research, Click chemistry is extensively utilized for drug delivery applications. The exhibited bio-compatibility and dormancy towards other biological components under cellular environments makes Click chemistry an identified boon in bio-medical research. In this review, various click-derived transition metal complexes are discussed in terms of their applications and uniqueness. The scope of this chemistry towards other streams of applied sciences is also discussed.

Synthesis, crystal structure and Hirshfeld surface analysis of (4-methyl-phen-yl)[1-(penta-fluoro-phen-yl)-5-(tri-fluoro-meth-yl)-1H-1,2,3-triazol-4-yl]methanone

The title compound, C17H7F8N3O, was obtained via the reaction of 1-azido-2,3,4,5,6-penta-fluoro-benzene with 4,4,4-tri-fluoro-1-(p-tol-yl)butane-1,3-dione using tri-ethyl-amine as a base catalyst and solvent. The dihedral angles between the penta-fluoro-phenyl (A), triazole (B) and p-tolyl (C) rings are A/B = 62.3 (2), B/C = 43.9 (3) and A/C = 19.1 (3)°. In the crystal, the mol-ecules are linked by C-H⋯F and C-H⋯O hydrogen bonds as well as by aromatic π-π stacking inter-actions into a three-dimensional network. To further analyse the inter-molecular inter-actions, a Hirshfeld surface analysis was performed.

Azo-triazolide bis-cyclometalated Ir(iii) complexes via cyclization of 3-cyanodiarylformazanate ligands

In this work we describe the synthesis of sterically encumbered 1,5-diaryl-3-cyanoformazanate bis-cyclometalated iridium(iii) complexes, two of which undergo redox-neutral cyclization during the reaction to produce carbon-bound 2-aryl-4-arylazo-2H-1,2,3-triazolide ligands. This transformation offers a method for accessing 2-aryl-4-arylazo-2H-1,2,3-triazolide ligands, a heretofore unreported class of chelating ligands. One formazanate complex and both triazolide complexes are structurally characterized by single-crystal X-ray diffraction, with infrared spectroscopy being the primary bulk technique to distinguish the formazanate and triazolide structures. All complexes are further characterized by UV-Vis absorption spectroscopy and cyclic voltammetry, with the triazolide compounds having similar frontier orbital energies to the formazanate complexes but much less visible absorption.

Mechanochemical changes on cyclometalated Ir(iii) acyclic carbene complexes – design and tuning of luminescent mechanochromic transition metal complexes

A new class of luminescent cyclometalated Ir(iii) complexes with readily tunable mechanochromic properties derived from the mechanically induced trans-to-cis isomerization have been developed.

Mixed annihilation electrogenerated chemiluminescence of iridium(iii) complexes

Previously reported annihilation ECL of mixtures of metal complexes have generally comprised Ir(ppy)3 or a close analogue as a higher energy donor/emitter (green/blue light) and [Ru(bpy)3]2+ or its derivative as a lower energy acceptor/emitter (red light). In contrast, here we examine Ir(ppy)3 as the lower energy acceptor/emitter, by combining it with a second Ir(iii) complex: [Ir(df-ppy)2(ptb)]+ (where ptb = 1-benzyl-1,2,3-triazol-4-ylpyridine). The application of potentials sufficient to attain the first single-electron oxidation and reduction products can be exploited to detect Ir(ppy)3 at orders of magnitude lower concentration, or enhance its maximum emission intensity at high concentration far beyond that achievable through conventional annihilation ECL of Ir(ppy)3 involving comproportionation. Moreover, under certain conditions, the colour of the emission can be selected through the applied electrochemical potentials. We have also prepared a novel Ir(iii) complex with a sufficiently low reduction potential that the reaction between its reduced form and Ir(ppy)3+ cannot populate the excited state of either luminophore. This enabled, for the first time, the exclusive formation of either excited state through the application of higher cathodic or anodic potentials, but in both cases, the ECL was greatly diminished by parasitic dark reactions.

Computational investigations of click-derived 1,2,3-triazoles as keystone ligands for complexation with transition metals: a review

In recent years, metal complexes of organo 1,2,3-triazole click-derived ligands have attracted significant attention as catalysts in many chemical transformations and also as biological and pharmaceutical active agents. Regarding the important applications of these metal-organo 1,2,3-triazole-based complexes, in this review, we focused on the recently reported investigations of the structural, electronic, and spectroscopic aspects of the complexation process in transition metal complexes of 1,2,3-triazole-based click ligands. In line with this, the coordination properties of these triazole-based click ligands with transition metals were studied via several quantum chemistry calculations. Moreover, considering the complexation process, we have presented comparative discussions between the computational results and the available experimental data.

Room temperature transmetallation from tris(pentafluorophenyl)borane to cyclometallated iridium(iii)

Transmetallation with tris(pentafluorophenyl)borane produces bis-cyclometallated iridium complexes with a perfluorophenyl ancillary ligand.

An unexpected journey from highly tunable phosphorescence to novel photochemistry of 1,2,3-triazole-based complexes

Complexes containing the humble 1,2,3-triazole ring moiety have enabled access to highly tunable with efficient phosphorescence but have also in facilitated access to novel photoreactive excited states yielding highly unusual photochemical reactivity.

Luminescent Iridium(III) Cyclometalated Complexes with 1,2,3-Triazole "Click" Ligands

A series of cyclometalated iridium(III) complexes with either 4-(2-pyridyl)-1,2,3-triazole or 1-(2-picolyl)-1,2,3-triazole ancillary ligands to give complexes with either 5- or 6-membered chelate rings were synthesized and characterized by a combination of X-ray crystallography, electron spin ionization-high-resolution mass spectroscopy (ESI-HRMS), and nuclear magnetic resonance (NMR) spectroscopy. The electronic properties of the complexes were probed using absorption and emission spectroscopy, as well as cyclic voltammetry. The relative stability of the complexes formed from each ligand class was measured, and their excited-state properties were compared. The emissive properties are, with the exception of complexes that contain a nitroaromatic substituent, insensitive to functionalization of the ancillary pyridyl-1,2,3-triazole ligand but tuning of the emission maxima was possible by modification of the cyclometalating ligands. It is possible to prepare a wide range of optimally substituted pyridyl-1,2,3-triazoles using copper Cu(I)-catalyzed azide alkyne cycloaddition, which is a commonly used "click" reaction, and this family of ligands represent an useful alternative to bipyridine ligands for the preparation of luminescent iridium(III) complexes.

Protein Labelling with Versatile Phosphorescent Metal Complexes for Live Cell Luminescence Imaging

To take advantage of the luminescent properties of d(6) transition metal complexes to label proteins, versatile bifunctional ligands were prepared. Ligands that contain a 1,2,3-triazole heterocycle were synthesised using Cu(I) catalysed azide-alkyne cycloaddition "click" chemistry and were used to form phosphorescent Ir(III) and Ru(II) complexes. Their emission properties were readily tuned, by changing either the metal ion or the co-ligands. The complexes were tethered to the metalloprotein transferrin using several conjugation strategies. The Ir(III)/Ru(II)-protein conjugates could be visualised in cancer cells using live cell imaging for extended periods without significant photobleaching. These versatile phosphorescent protein-labelling agents could be widely applied to other proteins and biomolecules and are useful alternatives to conventional organic fluorophores for several applications.

Comparison of inverse and regular 2-pyridyl-1,2,3-triazole "click" complexes: structures, stability, electrochemical, and photophysical properties

Two inverse 2-pyridyl-1,2,3-triazole "click" ligands, 2-(4-phenyl-1H-1,2,3-triazol-1-yl)pyridine and 2-(4-benzyl-1H-1,2,3-triazol-1-yl)pyridine, and their palladium(II), platinum(II), rhenium(I), and ruthenium(II) complexes have been synthesized in good to excellent yields. The properties of these inverse "click" complexes have been compared to the isomeric regular compounds using a variety of techniques. X-ray crystallographic analysis shows that the regular and inverse complexes are structurally very similar. However, the chemical and physical properties of the isomers are quite different. Ligand exchange studies and density functional theory (DFT) calculations indicate that metal complexes of the regular 2-(1-R-1H-1,2,3-triazol-4-yl)pyridine (R = phenyl, benzyl) ligands are more stable than those formed with the inverse 2-(4-R-1H-1,2,3-triazol-1-yl)pyridine (R = phenyl, benzyl) "click" chelators. Additionally, the bis-2,2'-bipyridine (bpy) ruthenium(II) complexes of the "click" chelators have been shown to have short excited state lifetimes, which in the inverse triazole case, resulted in ejection of the 2-pyridyl-1,2,3-triazole ligand from the complex. Under identical conditions, the isomeric regular 2-pyridyl-1,2,3-triazole ruthenium(II) bpy complexes are photochemically inert. The absorption spectra of the inverse rhenium(I) and platinum(II) complexes are red-shifted compared to the regular compounds. It is shown that conjugation between the substituent group R and triazolyl unit has a negligible effect on the photophysical properties of the complexes. The inverse rhenium(I) complexes have large Stokes shifts, long metal-to-ligand charge transfer (MLCT) excited state lifetimes, and respectable quantum yields which are relatively solvent insensitive.

Singlet oxygen generation by cyclometalated complexes and applications

While cyclometalated complexes have been extensively studied for optoelectronic applications, these compounds also represent a relatively new class of photosensitizers for the production of singlet oxygen. Thus far, singlet oxygen generation from cyclometalated Ir and Pt complexes has been studied in detail. In this review, photophysical data for singlet oxygen generation from these complexes are presented, and the mechanism of (1) O2 generation is discussed, including evidence for singlet oxygen generation via an electron-transfer mechanism for some of cyclometalated Ir complexes. The period from the first report of singlet oxygen generation by a cyclometalated Ir complex in 2002 through August 2013 is covered in this review. This new class of singlet oxygen photosensitizers may prove to be rather versatile due to the ease of substitution of ancillary ligands without loss of activity. Several cyclometalated complexes have been tethered to zeolites, polystyrene, or quantum dots. Applications for photooxygenation of organic molecules, including "traditional" singlet oxygen reactions (ene reaction, [4 + 2] and [2 + 2] cycloadditions) as well as oxidative coupling of amines are presented. Potential biomedical applications are also reviewed.