Dinuclear Iridium Research Articles

Near Infrared-Fluorescent Dinuclear Iridium(III) Nanoparticles for Immunogenic Sonodynamic Therapy.

Dinuclear iridium(III) complexes activated by light-inducible spatiotemporal control are emerging as promising candidates for cancer therapy. However, broader applications of current light-activated dinuclear iridium(III) complexes are limited by the ineffective tissue penetration and undesirable feedback on guidance activation. Here, an ultrasound (US) triggered near infrared-fluorescent dinuclear iridium(III) nanoparticle, NanoIr, is first reported to precisely and spatiotemporally inhibit tumor growth. It is demonstrated that reactive oxygen species can be generated by NanoIr upon exposure to US irradiation (NanoIr + US), thereby inducing immunogenic cell death. When combined with cisplatin, NanoIr + US elicits synergistic effects in patient-derived tumor xenograft mice models of ovarian cancer. This work first provides a design of dinuclear iridium(III) nanoparticles for immunogenic sonodynamic therapy.

Atomically dispersed dinuclear iridium active sites for efficient and stable electrocatalytic chlorine evolution reaction.

The electrochemical chlorine evolution reaction (CER) is a critical anode reaction in chlor-alkali electrolysis. Although precious metal-based mixed metal oxides (MMOs) have long been used as CER catalysts, they suffer from high cost and poor selectivity due to the competing oxygen evolution reaction (OER). Single-atom catalysts (SACs), featuring high atom utilization efficiency, have captured widespread interest in diverse applications. However, the single-atom sites in SACs are generally recognized as independent motifs and the interplay of adjacent sites is largely overlooked. Herein, we report a "precursor-preselected" cage-encapsulated strategy to synthesize atomically dispersed dinuclear iridium active sites bridged by oxygen that are supported on nitrogen-doped carbon (Ir2-ONC). The dinuclear Ir2-ONC catalyst exhibits a CER onset potential of 1.375 V vs. normal hydrogen electrode, a high faradaic efficiency of >95%, and a high mass activity of 14321.6 A gIr -1, much better than the Ir SACs, which demonstrates the significance of coordination and electronic structure regulation for atomically dispersed catalysts. Density functional theory calculations and ab initio molecular dynamics simulations confirm that the unique dinuclear structure facilitates Cl- adsorption, resulting in improved catalytic CER performance.

193Ir nuclear forward scattering of an iridium(I) complex

Synchrotron based nuclear forward scattering (NFS) experiments using the 193Ir nucleus have been performed for the first time on a dinuclear iridium(I) complex, [IrCl(COD)]2 with COD being cycloocta-1,5-diene. This complex serves as a catalyst for hydrogenation and other chemical reactions. Both, the obtained absolute values of the isomer shift δ=0.87mm s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta =0.87 \\ {\ ext{mm s}}^{-1}$$\\end{document} and the quadrupole splitting ΔEQ=3.82mm s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varDelta {E}_{Q}=3.82 \\ {\ ext{mm s}}^{-1}$$\\end{document} agree within the experimental error with values obtained via conventional 193Ir Mössbauer spectroscopy reported earlier (Gál M. et al. J. Radioanal. Nucl. Chem., 260 (1) 2004, 133). In addition, we present density functional theory (DFT) calculations of the complex yielding its electronic structure and related Mössbauer parameters.

Photochromic dinuclear iridium(III) complexes having phenoxyl-imidazolyl radical complex derivatives.

We demonstrate that the phenoxyl-imidazolyl radical complex (PIC), which is a rate-tunable fast photoswitch, can be used as a ligand that directly coordinates with iridium (III) ions. The iridium complexes show the characteristic photochromic reactions originating from the PIC moiety, whereas the behaviour of transient species is substantially different from that of the PIC.

Thermally activated delayed fluorescence in a deep red dinuclear iridium(iii) complex: a hidden mechanism for short luminescence lifetimes

Thermally activated delayed fluorescence (TADF) is found to play an important role in accelerating the rate of radiative decay in luminescent iridium(iii) complexes, shown in this instance for dinuclear complexes formed with high stereoselectivity.

Ligand effect of cyclometallated iridium(iii) complexes on N-alkylation of amines in hydrogen borrowing reactions.

Dinuclear iridium complexes with the general formula (C^N)2Ir(μ-Cl)2Ir(C^N)2 (C^N = bidentate ligand with carbon and nitrogen donor atoms) were prepared and used in catalytic systems for N-alkylation of amines through the hydrogen borrowing pathway. Triphenylphosphine derivatives were used as auxiliary in catalytic systems to provide excellent conversion of amines to N-alkylation products in yields ranging from 57% to 100%. The catalytic ability of the catalyst depends on the structure of its coordination ligands, including bidentate ligands (C^N) and triphenylphosphine derivatives. These catalytic systems adopt an environmentally friendly and sustainable reaction process through a hydrogen self-transfer strategy, using readily available alcohols as alkylating agents without the need for bases, solvents, and other additives, showing potential in the synthetic and pharmaceutical industries.

Structure-property relationships of photofunctional diiridium(II) complexes with tetracationic charge and an unsupported Ir–Ir bond

In contrast to the extensively studied dirhodium(II) complexes and iridium(III) complexes, neutral or dicationic dinuclear iridium(II) complexes with an unsupported ligand are underdeveloped. Here, a series of tetracationic dinuclear iridium(II) complexes, featuring the unsupported Ir(II)–Ir(II) single bond with long bond distances (2.8942(4)–2.9731(4) Å), are synthesized and structurally characterized. Interestingly, compared to the previous unsupported neutral or dicationic diiridium(II) complexes, our DFT and high-level DLPNO-CCSD(T) results found the largest binding energy in these tetracationic complexes even with the long Ir(II)–Ir(II) bond. Our study further reveals that London dispersion interactions enhance the stability cooperatively and significantly to overcome the strong electrostatic repulsion between two half dicationic metal fragments. This class of complexes also exhibit photoluminescence in solution and solid states, which, to our knowledge, represents the first example of this unsupported dinuclear iridium(II) system. In addition, their photoreactivity involving the generation of iridium(II) radical monomer from homolytic cleavage was also explored. The experimental results of photophysical and photochemical behaviours were also correlated with computational studies.

Rational Design of Mono- and Bi-Nuclear Cyclometalated Ir(III) Complexes Containing Di-Pyridylamine Motifs: Synthesis, Structure, and Luminescent Properties.

Heteroleptic cyclometalated iridium (III) complexes (1–3) containing di-pyridylamine motifs were prepared in a stepwise fashion. The presence of the di-pyridylamine ligands tunes their electronic and optical properties, generating blue phosphorescent emitters at room temperature. Herein we describe the synthesis of the mononuclear iridium complexes [Ir(ppy)2(DPA)][OTf] (1), (ppy = phenylpyridine; DPA = Dipyridylamine) and [Ir(ppy)2(DPA-PhI)][OTf] (2), (DPA-PhI = Dipyridylamino-phenyliodide). Moreover, the dinuclear iridium complex [Ir(ppy)2(L)Ir(ppy)2][OTf]2 (3) containing a rigid angular ligand “L = 3,5-bis[4-(2,2′-dipyridylamino)phenylacetylenyl]toluene” and displaying two di-pyridylamino groups was also prepared. For comparison purposes, the related dinuclear rhodium complex [Rh (ppy)2(L)Rh(ppy)2][OTf]2 (4) was also synthesized. The x-ray molecular structure of complex 2 was reported and confirmed the formation of the target molecule. The rhodium complex 4 was found to be emissive only at low temperature; in contrast, all iridium complexes 1–3 were found to be phosphorescent in solution at 77 K and room temperature, displaying blue emissions in the range of 478–481 nm.

Single‐Cell Quantification of a Highly Biocompatible Dinuclear Iridium(III) Complex for Photocatalytic Cancer Therapy

AbstractQuantifying the content of metal‐based anticancer drugs within single cancer cells remains a challenge. Here, we used single‐cell inductively coupled plasma mass spectrometry to study the uptake and retention of mononuclear (Ir1) and dinuclear (Ir2) IrIII photoredox catalysts. This method allowed rapid and precise quantification of the drug in individual cancer cells. Importantly, Ir2 showed a significant synergism but not an additive effect for NAD(P)H photocatalytic oxidation. The lysosome‐targeting Ir2 showed low dark toxicity in vitro and in vivo. Ir2 exhibited high photocatalytic therapeutic efficiency at 525 nm with an excellent photo‐index in vitro and in tumor‐bearing mice model. Interestingly, the photocatalytic anticancer profile of the dinuclear Ir2 was much better than the mononuclear Ir1, indicating for the first time that dinuclear metal‐based photocatalysts can be applied for photocatalytic anticancer treatment.

Single-Cell Quantification of a Highly Biocompatible Dinuclear Iridium(III) Complex for Photocatalytic Cancer Therapy.

Quantifying the content of metal-based anticancer drugs within single cancer cells remains a challenge. Here, we used single-cell inductively coupled plasma mass spectrometry to study the uptake and retention of mononuclear (Ir1) and dinuclear (Ir2) IrIII photoredox catalysts. This method allowed rapid and precise quantification of the drug in individual cancer cells. Importantly, Ir2 showed a significant synergism but not an additive effect for NAD(P)H photocatalytic oxidation. The lysosome-targeting Ir2 showed low dark toxicity in vitro and in vivo. Ir2 exhibited high photocatalytic therapeutic efficiency at 525 nm with an excellent photo-index in vitro and in tumor-bearing mice model. Interestingly, the photocatalytic anticancer profile of the dinuclear Ir2 was much better than the mononuclear Ir1, indicating for the first time that dinuclear metal-based photocatalysts can be applied for photocatalytic anticancer treatment.

Highly Luminescent Dinuclear Iridium(III) Complexes Containing Phenanthroline-Based Neutral Ligands as Chemosensors for Cu2+ Ion

Highly Luminescent Dinuclear Iridium(III) Complexes Containing Phenanthroline-Based Neutral Ligands as Chemosensors for Cu²⁺ Ion

Synthesis and catalytic application of new [{IrCl(cod)}2(μ2-diNHC)] and [{Ir(cod)(sulfonated phosphine)}2(μ2-diNHC)] complexes

Four new dinuclear iridium(I) complexes were synthesized from the di(N-heterocyclic carbene) ligand precursors 1,1′-methylene-bis(3-benzyl-imidazolium)dichloride and 1,1′-methylene-bis(3-(2,4,6-trimethylbenzyl)imidazolium)dichloride. The complexes were fully characterized by spectroscopic methods, HR-MS (ESI) spectrometry, furthermore, the structure of complexes 1 and 2 were determined by single-crystal X-ray diffraction. Complexes 3a and 3b which have sulfonated triphenylphosphine ligands, were successfully used under mild conditions as catalysts in reduction reaction of ketones via hydrogen transfer from aqueous 2-propanol, and for hydrogenation of alkynes in aqueous-organic biphasic systems.

Synthesis and optoelectronic properties of a dinuclear iridium (III) complex containing a picolinic acid derivative by nonconjugated linkage with a D-A-D core

A novel dinuclear iridium (Ⅲ) complex containing a non- conjugated bridging picolinic acid ligand of (C8TPAPhOC2FIrpic)2BT with a D-A-D core was synthesized and characterized, in which the D-A-D core consists of benzo[c][1,2,5]thiadiazole (BT) and triphenylamino (TPA) units. Its optophysical, electrochemical and electroluminescent characteristics were primarily studied. It is found this dinuclear iridium (Ⅲ) complex exhibited similar photoluminescent and electroluminescent profiles, but higher brightness and efficiency in compared with the picolinic acid ligand in the single-emissive-layer organic light-emitting devices. The maximum luminance of 7404 cd/m2 and current efficiency of 0.81 cd/A was obtained in the (C8TPAPhOC2FIrpic)2BT-based devices. The efficient energy transfer is observed from the terminal iridium complex unit to the picolinic acid ligand. This work demonstrates that the picolinic acid ligand with a D-A-D core can facilitate dinuclear iridium (III) complex to exhibit the ancillary ligand-based red emission.

Accessing Molecular Dimeric Ir Water Oxidation Catalysts from Coordination Precursors.

One ongoing challenge in the field of iridium-based water oxidation catalysts is to develop a molecular precatalyst affording well-defined homogeneous active species for catalysis. Our previous work by using organometallic precatalysts Cp*Ir(pyalk)OH and Ir(pyalk)(CO)2 (pyalk = (2-pyridyl)-2-propanolate) suggested a μ-oxo-bridged Ir dimer as the probable resting state, although the structure of the active species remained elusive. During the activation, the ligands Cp* and CO were found to oxidatively degrade into acetic acid or other products, which coordinate to Ir centers and affect the catalytic reaction. Two related dimers bearing two pyalk ligands on each iridium were crystallized for structural analysis. However, preliminary results indicated that these crystallographically characterized dimers are not active catalysts. In this work, we accessed a mixture of dinuclear iridium species from a coordination precursor, Na[Ir(pyalk)Cl4], and assayed their catalytic activity for oxygen evolution by using NaIO4 as the oxidant. This catalyst showed comparable oxygen-evolution activity to the ones previously reported from organometallic precursors without demanding oxidative activation to remove sacrificial ligands. Future research along this direction is expected to provide insights and design principles toward a well-defined active species.

Dinuclear iridium complexes with non-conjugated ditopic bis-terdentate cyclometallating ligands and their electroluminescence properties

Two dinuclear iridium(III) complexes (3, 4) with a new bridged cyclometallating bis-tripodal phosphite ligand and two correspongding mononuclear complexes (1, 2) have been synthesized. The effects of different substituents and adding iridium atoms on the photophysical properties of these iridium complexes are studied. These dinuclear complexes have excellent thermal stability with decomposition temperatures exceeding 440 °C, which are more than 70 °C higher than that of mononuclear complexes. The dinuclear complexes possess higher quantum yields and lower nonradiative decay rates than the mononuclear complexes due to the increased heavy atom effect and molecular rigidity. The steric protective tertiary butyl groups on 2, 2′-bipyridine unit also improve the quantum yields and reduce the nonradiative decay rates of iridium complexes. The dinuclear complexes exhibit higher oxidation potential (0.579–0.594 V) than the mononuclear complexes (0.558–0.560 V). The organic light-emitting diodes based on complex 2 shows a turn-on voltage of 3.8 V, high maximum brightness of 9550 cd m−2 with moderate external quantum efficiency (EQE) of 5.1%. The device based on complex 4 shows lower turn-on voltage of 3.2 V, higher maximum brightness of 9639 cd m−2, but with lower EQE of 2.2% because of the serious concentration quenching.

Light-Assisted Catalytic Hydrogenation of Carbon Dioxide at a Low Pressure by a Dinuclear Iridium Polyhydride Complex

A dinuclear iridium pentahydride complex bearing a diphosphine ligand with a fluorene backbone was synthesized and characterized for use as a photocatalyst for CO2 hydrogenation. The complex can be...

Synthesis, characterization of mechanochromic luminescent-active mono-/dinuclear iridium(III) complexes with near-infrared emission

Iridium(III) complexes with near-infrared (NIR) emission are still less well developed. In this work, two new NIR emissive mono- and dinuclear iridium complexes were designed and synthesized via introducing the tetraphenlyethene Schiff base ligands. Interestingly, both complexes display mechanochromic luminescent (MCL) behavior, and the MCL mechanism can be attributed to the atypical physical phase transformations from amorphization to crystallization.

Selective Double CH Activation at a Methylene Carbon in Methylenediphenol Derivatives to Generate Carbene-Bridged Dinuclear Iridium Complexes

Double CH activation at a bridging methylene group in methylenediphenols to generate carbene-bridged dinuclear iridium complexes is presented. Reaction of 2,2′-methylenediphenol derivatives CH2(C6H...

Near Infrared Phosphorescent Dinuclear Ir(III) Complex Exhibiting Unusually Slow Intersystem Crossing and Dual Emissive Behavior.

A dinuclear iridium(III) complex IrIr shows dual emission consisting of near infrared (NIR) phosphorescence (λmax = 714 nm, CH2Cl2, T = 300 K) and green fluorescence (λmax = 537 nm). The NIR emission stems from a triplet state (T1) localized on the ditopic bridging ligand (3LC). Because of the dinuclear molecular structure, the phosphorescence efficiency (ΦPL = 3.5%) is high compared to those of other known red/NIR-emitting iridium complexes. The weak fluorescence stems from the lowest excited singlet state (S1) of 1LC character. The occurrence of fluorescence is ascribed to relatively slow intersystem crossing (ISC) from state S1 (1LC) to the triplet manifold. The measured ISC rate corresponds to a time constant τISC of 2.1 ps, which is an order of magnitude longer than those usually found for iridium complexes. This slow ISC rate can be explained in terms of the LC character and large energy separation (0.57 eV) of the respective singlet and triplet excited states. IrIr is internalized by live HeLa cells as evidenced by confocal luminescence microscopy.

Bimetallic Reactivities of Dinuclear Iridium and Rhodium Complexes Generated from Two Types of Alkyne‐Containing Bisphosphine Ligands

We have investigated the reactivities of a series of dinuclear iridium(II,II) and rhodium(II,II) 1,3‐butadiene‐1,4‐diyl complexes derived from two types of alkyne‐containing ligands. Newly developed ligand 2 afforded 2nd generation diiridium complexes that have higher reactivity toward halide substitution and acetylide formation. The significant differences in reactivity, influenced by the 1,3‐butadiene‐1,4‐diyl ligand backbone of these complexes, have been systematically investigated by synthetic studies as well as X‐ray crystallographic and spectroscopic analyses.