Iridium Center Research Articles

A Dual‐Purpose Non‐Canonical Amino Acid for the Expanded Genetic Code: Combining Metal‐Binding and Click Chemistry

AbstractA rationally designed dual‐purpose non‐canonical amino acid (Trz) has been synthesised and successfully incorporated into a protein scaffold by genetic code expansion. Trz contains a 5‐pyridyl‐1,2,4‐triazine system, which allows for inverse‐electron‐demand Diels–Alder (IEDDA) reactions to occur on the triazine ring and for metal ions to be chelated both before and after the click reaction. Trz was successfully incorporated into a protein scaffold and the IEDDA utility of Trz demonstrated through the site‐specific labelling of the purified protein with a bicyclononyne. Additionally, Trz was shown to successfully coordinate a cyclometallated iridium(III) centre, providing access to a bioorthogonal luminogenic probe. The luminescent properties of the Ir(III)‐bound protein blue‐shift upon IEDDA click reaction with bicyclononyne, providing a unique method for monitoring the extent and location of the labelling reaction. In summary, Trz is a new dual‐purpose non‐canonical amino acid with great potential for myriad bioapplications where metal‐based functionality is required, for example in imaging, catalysis, and photo‐dynamic therapy, in conjunction with a bioorthogonal reactive handle to impart additional functionalities, such as dual‐modality imaging or therapeutic payloads.

A Dual-Purpose Non-Canonical Amino Acid for the Expanded Genetic Code: Combining Metal-Binding and Click Chemistry.

A rationally designed dual-purpose non-canonical amino acid (Trz) has been synthesised and successfully incorporated into a protein scaffold by genetic code expansion. Trz contains a 5-pyridyl-1,2,4-triazine system, which allows for inverse-electron-demand Diels-Alder (IEDDA) reactions to occur on the triazine ring and for metal ions to be chelated both before and after the click reaction. Trz was successfully incorporated into a protein scaffold and the IEDDA utility of Trz demonstrated through the site-specific labelling of the purified protein with a bicyclononyne. Additionally, Trz was shown to successfully coordinate a cyclometallated iridium(III) centre, providing access to a bioorthogonal luminogenic probe. The luminescent properties of the Ir(III)-bound protein blue-shift upon IEDDA click reaction with bicyclononyne, providing a unique method for monitoring the extent and location of the labelling reaction. In summary, Trz is a new dual-purpose non-canonical amino acid with great potential for myriad bioapplications where metal-based functionality is required, for example in imaging, catalysis, and photo-dynamic therapy, in conjunction with a bioorthogonal reactive handle to impart additional functionalities, such as dual-modality imaging or therapeutic payloads.

Hydrogen Sulfide-Induced Activatable Photodynamic Therapy Adjunct to Disruption of Subcellular Glycolysis in Cancer Cells by a Fluorescence-SERS Bimodal Iridium Metal-Organic Hybrid.

The practical application of photodynamic therapy (PDT) demands targeted and activatable photosensitizers to mitigate off-target phototoxicity common in "always on" photosensitizers during light exposure. Herein, a cyclometalated iridium complex-based activatable photodynamic molecular hybrid, Cy-Ir-7-nitrobenzofurazan (NBD), is demonstrated as a biomedicine for molecular precision. This design integrates a hydrogen sulfide (H2S)-responsive NBD unit with a hydroxy-appended iridium complex, Cy-Ir-OH. In normal physiological conditions, the electron-rich Ir metal center exerts electron transfer to the NBD unit, quenches the excited state dynamics, and establishes a PDT-off state. Upon exposure to H2S, Cy-Ir-NBD activates into the potent photosensitizer Cy-Ir-OH through nucleophilic substitution. This mechanism ensures exceptional specificity, enabling targeted phototherapy in H2S-rich cancer cells. Additionally, we observed that Cy-Ir-NBD-induced H2S depletion disrupts S-sulfhydration of the glyceraldehyde-3-phosphate dehydrogenase enzyme, impairing glycolysis and ATP production in the cellular milieu. This sequential therapeutic process of Cy-Ir-NBD is governed by the positively charged central iridium ion that ensures mitochondria-mediated apoptosis in cancer cells. Dual-modality SERS and fluorescence imaging validate apoptotic events, highlighting Cy-Ir-NBD as an advanced theranostic molecular entity for activatable PDT. Finally, as a proof of concept, clinical assessment is evaluated with the blood samples of breast cancer patients and healthy volunteers, based on their H2S overexpression capability through SERS and fluorescence, revealing Cy-Ir-NBD to be a promising predictor for PDT activation in advanced cancer phototherapy.

Air‐Stable Bis‐Cyclometallated Iridium Catalysts for Ortho‐Directed C(sp2)−H Borylation

AbstractWe report a class of isolable bis‐cyclometallated iridium precatalysts (ImIr) and their use in regioselective ortho−C−H borylation of aromatic, heteroaromatic, acrylic, and aliphatic systems. The catalysts consist of two imine ligands and an acetate coordinated to an iridium (III) center. The isolable character of ImIr warrants its compatibility with high‐throughput experimentation, a prerequisite for applications in late‐stage functionalization (LSF) of complex substrates. Initial mechanistic studies point towards an inner‐sphere mechanism involving bis‐cyclometallated species shedding light on the general mechanistic understanding of ortho‐selective C−H borylations.

Synthesis and catalytic activity of half‐sandwich iridium complexes with acylhydrazone ligands for N‐alkylation of hydrazides under mild conditions

A new [Cp*IrClL] half‐sandwich iridium complex was successfully synthesized by coordinating an acylhydrazone ligand with [Cp*IrCl2]2, followed by comprehensive characterization using various spectroscopic and analytical techniques. Complex 3 was subjected to crystal structure analysis, revealing that the acylhydrazone ligand coordinates with the iridium through bidentate coordination involving the imidolate oxygen and imine nitrogen atoms. This interaction resulted in the formation of a pseudo‐octahedral geometry with the iridium center. The iridium complexes 1–4, which are stable in the presence of air and moisture, exhibit significant catalyst performance in the N‐alkylation reactions of hydrazides under gentle reaction conditions. This iridium complex catalyzes various types of alcohols to undergo N‐alkylation reactions with acyl hydrazides via a one‐pot method, yielding diverse N‐alkylated hydrazide derivatives. The catalyst displayed exceptional catalytic efficiency, a broad variety of substrates, and gentle reaction conditions, indicating its significant potential for industrial applications.

Synthesis, structure and effects of an azoimine functionalized iridium complex on cancer cells

A novel ligand L having azoimine bond with quinoline moiety reacts with [(2-ppy)2Ir(μ-Cl)]2 in dichloromethane medium to produce an iridium(III) complex of composition [Ir(2-ppy)2(L)]. Here, the iridium centre is bound to neutral bidentate N, N donating sites of the ligand (L), where the azo part of L is not involved in chelation. The ligand and complex are characterized by elemental analysis, NMR spectroscopy, ESI-MS mass spectrometry, FTIR, UV–Vis and luminescence spectroscopic techniques. The ligand structure and the geometry around iridium centre of complex [Ir(2-ppy)2(L)] is confirmed by the single-crystal X-ray diffraction (XRD) method. DFT studies were also performed to support the experimental aspects of the complex as well as electronic distribution in molecular orbitals of various energy states. The complex exhibits blue emission band at 428 nm with quantum yield (Φ) 0.136. Further, in vitro analysis of the anticancer activity of the complex was studied mainly with the MCF - 7 cell line. The results showed that the complex have good IC50 values when compared to the standard drug cisplatin.

Aqueous emissive cyclometalated iridium photoreductants: synthesis, computational analysis and the photocatalytic reduction of 4-nitrophenol.

Herein, we present luminescent mononuclear iridium complexes [1]3+-[4]3+ using NEt3-appended C^N chelating benzimidazole (L1-L4) and semi-flexible phenanthroline-pyrazine-based (phpy) ligands exhibiting photocatalytic reduction of 4-nitrophenol (4-NP) in the presence of NEt3 in an aqueous medium. The formation of [1]3+-[4]3+ was confirmed by HRMS, 1H-1H COSY, and 13C and 19F NMR spectroscopy. The complex [4]3+ is water soluble, whereas the others ([1]3+-[3]3+) are partially soluble. The complexes are luminescent in both CH3CN and H2O media. The DFT study reveals that the HOMO of [1]3+ resides on the C^N chelating benzimidazole and iridium center. However, it moves to the pyrazine-pyridine of the phpy unit in the case of [2]3+-[4]3+. The LUMOs are localized on the phenanthroline unit of phpy for all the complexes. This suggests an important role of the fluorine atom on electron density distribution. Spin density analysis demonstrates that the emission bands of the complexes arise from 3MLLCT states. The complex [4]3+ displays promising photocatalytic activity towards 4-NP photoreduction, whereas complexes [1]3+-[3]3+ exhibit lower reactivity. The mechanistic study suggests that the reaction proceeds through an oxidative quenching pathway, where 4-NP is reduced by accepting an electron from excited [Ir(III)] and gets oxidized to Ir(IV), which comes back to its original Ir(III) state by accepting an electron from the sacrificial electron donor NEt3.

Selenosalicylate; a little-studied heavy-element analogue of the versatile thiosalicylate ligand.

Selenosalicylic acid (ortho-HSeC6H4CO2H), the heavy element congener of the widely studied thiosalicylic acid, was prepared by reaction of 2-carboxybenzenediazonium chloride (HO2CC6H4N2+Cl-) with Na2Se2, followed by reduction of the resulting diselenide (SeC6H4CO2H)2 with zinc and acetic acid. The coordination chemistry of the selenosalicylate ligand towards a variety of platinum(ii), palladium(ii), nickel(ii), gold(iii), gold(i), rhodium(iii), iridium(iii) and ruthenium(ii) centres was explored. X-ray crystal structure determinations were carried out on the complexes [Pt(SeC6H4CO2)(PPh3)2], [{(p-cym)Ru(SeC6H4CO2)}2] (p-cym = η6-p-cymene, CH3C6H4CH(CH3)2), [{Cp*Rh(SeC6H4CO2)}2] (Cp* = η5-C5Me5) and [Cp*Ir(SeC6H4CO2)(PPh3)], and comparisons are made with corresponding thiosalicylate complexes. The complexes were characterised by NMR spectroscopy as well as ESI mass spectrometry, which indicated a greater propensity for fragmentation including by selenium loss, compared to the thiosalicylate analogues. Hirshfeld surface analysis to visualise and quantify intermolecular interactions revealed the dominance of H⋯H contacts in [{(p-cym)Ru(SeC6H4CO2)}2] and [Cp*Ir(SeC6H4CO2)(PPh3)].

Synthesis, structure and optoelectronic properties of iridium(III) complexes bearing a four-membered Ir-N-C[sbnd]N chelate structure

Herein four novel iridium(III) complexes (tfpmd)2Ir(dpppy) (Ir1a, tfpmd = 2-(4-(trifluoromethyl) phenyl) pyrimidine, dpppy = P,P-diphenyl-N-(pyridin-2-yl)phosphinic amide), (tfpmd)2Ir(dppq) (Ir1b, dppq = P,P-diphenyl-N-(quinolin-2-yl)phosphinic amide), (tfpqz)2Ir(dpppy) (Ir2a, tfpzq = 4-(4-(trifluoromethyl) phenyl) quinazoline) and (tfpqz)2Ir(dppq) (Ir2b) were synthetized, and their structures, opto-physical, and electro-chemical properties were investigated in detail. The crystal structure shows that these complexes exhibit pseudo-octahedral geometry around iridium atom coordinated by C, N atoms from cyclometalated and ancillary ligands. Interestingly, two coordinated nitrogen atoms from the ancillary ligand form an unusual quaternary ring with the central iridium ion. Ir1a and Ir1b emit pure-green light with Commission Internationale de L'Eclairage (CIE) color coordinates of (0.25, 0.67) and (0.22, 0.67), respectively, in CH2Cl2 solution. With the increase of the degree of conjugation of the cyclometalated ligand from tfpmd to tfpqz, the luminescence of complexes Ir2a and Ir2b is greatly red-shifted, and pure-red emission with CIE coordinates of (0.66, 0.34) and (0.66, 0.34), respectively, is obtained. The photophysical behaviors were reasonably explained by quantum chemical calculations. The calculation results shows that their emission is ascribed to the mixed 3MLCT (metal-ligand charge transfer, dπ(Ir)→π*(cyclometalated ligand)) and 3LLCT (ligand-ligand charge transfer, π(ancillary ligand)→π*(cyclometalated ligand)) states. Owing to their good thermal and electrochemical stabilities, organic light emitting diode (OLED) devices with dual-emitting layer structure and a space interlayer were fabricated and exhibited high electroluminescent properties and mild efficiency roll-off (14%-21%).

Stabilizing iridium sites via interface and reconstruction regulations for water oxidation in alkaline and acidic media

Exploring effective iridium (Ir)-based electrocatalysts with stable iridium centers is highly desirable for oxygen evolution reaction (OER). Herein, we regulated the incorporation manner of Ir in Co3O4 support to stabilize the Ir sites for effective OER. When anchored on the surface of Co3O4 in the form of Ir(OH)6 species, the created Ir-OH-Co interface leads to a limited stability and poor acidic OER due to Ir leaching. When doped into Co3O4 lattice, the analyses of X-ray absorption spectroscopy, in-situ Raman, and OER measurements show that the partially replacement of Co in Co3O4 by Ir atoms inclines to cause strong electronic effect and activate lattice oxygen in the presence of Ir-O-Co interface, and simultaneously master the reconstruction effect to mitigate Ir dissolution, realizing the improved OER activity and stability in alkaline and acidic environments. As a result, Irlat@Co3O4 with Ir loading of 3.67 wt% requires 294 ± 4 mV / 285 ± 3 mV and 326 ± 2 mV to deliver 10 mA cm−2 in alkaline (0.1 M KOH / 1.0 M KOH) and acidic (0.5 M H2SO4) solution, respectively, with good stability.

Recent Advancement in the Synthesis of Ir-Based Complexes.

Cancer is a devastating disease with over 100 types, including lung and breast cancer. Cisplatin and metal-based drugs are limited due to their drug resistance and side effects. Iridium-based compounds have emerged as promising candidates due to their unique chemical properties and resemblance to platinum compounds. The objective of this study is to investigate the synthesis and categorization of iridium complexes, with a particular emphasis on their potential use as anticancer agents. The major focus of this research is to examine the synthesis of these complexes and their relevance to the field of cancer treatment. The negligible side effects and flexibility of cyclometalated iridium(III) complexes have garnered significant interest. Organometallic half-sandwich Ir(III) complexes have notable benefits in cancer research and treatment. The review places significant emphasis on categorizing iridium complexes according to their ligand environment, afterward considering the ligand density and coordination number. This study primarily focuses on several methods for synthesizing cyclometalated and half-sandwich Ir complexes, divided into subgroups based on ligand denticity. The coordination number of iridium complexes determines the number of ligands coordinated to the central iridium atom, which impacts their stability and reactivity. Understanding these complexes is crucial for designing compounds with desired properties and investigating their potential as anticancer agents. Cyclometalated iridium(III) complexes, which contain a meta-cycle with the E-M-C order σ bond, were synthesized in 1999. These complexes have high quantum yields, significant stock shifts, luminescence qualities, cell permeability, and strong photostability. They have been promising in biosensing, bioimaging, and phosphorescence of heavy metal complexes.

Aggregation-Induced Near-Infrared Emission and Electrochemiluminescence of an Iridium(III) Complex for Ampicillin Sodium Sensing.

A new iridium(III) complex was synthesized and characterized. Its photophysical properties and aggregation-induced emission and electrochemiluminescence in the near-infrared range were studied. The large conjugated cyclometallic ligand 1,2-phenylbenzoquinoline (pbq) was selected to form the Ir-C bond with the metal iridium(III) center and provide near-infrared emission of the complex. The auxiliary ligand 4,4'-diamino-2,2'-bipyridine (dabpy) can form hydrogen bonds, which was beneficial for the generation of aggregation-induced emission. The complex was aggregated into small spherical nanoparticles in 80% water and fascinating nanorings in 90% water. The sensing of ampicillin sodium (AMP) antibiotic by the iridium(III) complex were also investigated by photoluminescent and electrochemiluminescent methods. The complex showed a good selectivity toward AMP antibiotic compared to sodium phenylacetate and other eight antibiotics. The detection limits for AMP antibiotic was 0.76 μg/mL. This work provided a new strategy for the design of iridium(III) complex-based aggregation-induced emission and electrochemiluminescence probes for the sensing application.

Additive‐Free Transfer Hydrogenative Direct Asymmetric Reductive Amination Using a Chiral Pyridine‐Derived Half‐Sandwich Catalyst

AbstractChiral amines are broadly used compounds in pharmaceutical industry and organic synthesis, and reductive amination reactions have been the most appreciated methods for their syntheses. However, one‐step transfer hydrogenative direct asymmetric reductive amination (THDARA) that could expand the scope, simplify the operation and eliminate the use of additives has been challenging. In this work, based on the Xiao's racemic transfer hydrogenative reductive amination in 2010 and our recent work in novel chiral pyridine ligands, chiral half‐sandwich iridium catalysts were rationally designed and synthesized. Using the optimized catalyst and azeotropic mixture of formic acid and triethylamine as the hydrogen source, a broad range of α‐chiral (hetero)aryl amines, including various polar functional groups and heterocycles, were prepared in generally high yield and enantioselectivity under mild and operationally simple conditions. Density functional theory (DFT) calculation of the catalytically active Ir−H species and the key hydride transfer step supported the chiral pyridine‐induced stereospecific generation of the iridium center, and the enantioselection by taming the highly flexible key transition structure with multiple attractive non‐covalent interactions. This work introduced a type of effective chiral catalysts for simplified approach to medicinally important chiral amines, as well as a rare example of robust enantioselective transition‐metal catalysis.

Additive-Free Transfer Hydrogenative Direct Asymmetric Reductive Amination Using a Chiral Pyridine-Derived Half-Sandwich Catalyst.

Chiral amines are broadly used compounds in pharmaceutical industry and organic synthesis, and reductive amination reactions have been the most appreciated methods for their syntheses. However, one-step transfer hydrogenative direct asymmetric reductive amination (THDARA) that could expand the scope, simplify the operation and eliminate the use of additives has been challenging. In this work, based on the Xiao's racemic transfer hydrogenative reductive amination in 2010 and our recent work in novel chiral pyridine ligands, chiral half-sandwich iridium catalysts were rationally designed and synthesized. Using the optimized catalyst and azeotropic mixture of formic acid and triethylamine as the hydrogen source, a broad range of α-chiral (hetero)aryl amines, including various polar functional groups and heterocycles, were prepared in generally high yield and enantioselectivity under mild and operationally simple conditions. Density functional theory (DFT) calculation of the catalytically active Ir-H species and the key hydride transfer step supported the chiral pyridine-induced stereospecific generation of the iridium center, and the enantioselection by taming the highly flexible key transition structure with multiple attractive non-covalent interactions. This work introduced a type of effective chiral catalysts for simplified approach to medicinally important chiral amines, as well as a rare example of robust enantioselective transition-metal catalysis.

Size‐Controlled Synthesis of IrO2 Nanoparticles at High Temperatures for the Oxygen Evolution Reaction

AbstractIridium oxide is the state‐of‐the‐art catalyst for electrochemical water oxidation in an acidic medium. Despite being one of the rarest elements in the Earth's crust, there is a pressing need to maximize the utilization and longevity of active iridium centers. While conventional low‐temperature synthesis can yield nanostructures with high mass‐specific activity, they are often insufficiently stable during water oxidation. Structurally ordered iridium oxide is one of the most stable electrocatalysts utilized in polymer electrolyte membrane water electrolysis that benefits from the chemically ordered structure. However, its preparation requires thermal treatment at high temperatures, which improves its durability but can also result in reduced surface area and altered particle morphology. In this study, the challenge of controlling nanoparticle size during the preparation of structurally ordered iridium oxide is successfully addressed, which typically requires high‐temperature thermal treatment. By utilizing a silica nanoreactor as a hard template, a precise control is achieved over the nanoparticle size during high‐temperature thermal treatment. This approach maintains high durability while avoiding the common problem of reduced surface area and altered particle morphology. Specifically, this study is able to synthesize iridium oxide nanoparticles at temperatures up to 800 °C, while keeping their dimensions below 10 nm.

Iridium-Catalyzed 1,3-Rearrangement of Allylic Alcohols.

The allylic alcohol structural motif is prevalent in many important molecules and valuable building blocks. The rearrangement reaction is one of the most important transformations, however there are only a few reports for the 1,3-rearrangement of allylic alcohols. Herein, a 1,3-rearrangement of allylic alcohols catalyzed by an Ir(III) dihydride complex is described. This reaction could provide the corresponding less accessible allylic alcohols regio- and stereoselectively from readily available E/Z mixtures of the substrates. Furthermore, a tandem alkene isomerization followed by 1,3-rearrangement of homoallylic alcohols was also realized. In addition, this rearrangement reaction could be used to synthesize the natural product Navenone B. Mechanistic investigation indicated that the reaction pathway involved a π-allyl-Ir(V) intermediate and that the dihydride in the iridium catalyst acts as a hydrogen switch to modulate the valence of the iridium center.

Ligand Design and Preparation, Photophysical Properties, and Device Performance of an Encapsulated-Type Pseudo-Tris(heteroleptic) Iridium(III) Emitter.

The organic molecule 2-(1-phenyl-1-(pyridin-2-yl)ethyl)-6-(3-(1-phenyl-1-(pyridin-2-yl)ethyl)phenyl)pyridine (H3L) has been designed, prepared, and employed to synthesize the encapsulated-type pseudo-tris(heteroleptic) iridium(III) derivative Ir(κ6-fac-C,C',C″-fac-N,N',N″-L). Its formation takes place as a result of the coordination of the heterocycles to the iridium center and the ortho-CH bond activation of the phenyl groups. Dimer [Ir(μ-Cl)(η4-COD)]2 is suitable for the preparation of this compound of class [Ir(9h)] (9h = 9-electron donor hexadentate ligand), but Ir(acac)3 is a more appropriate starting material. Reactions were carried out in 1-phenylethanol. In contrast to the latter, 2-ethoxyethanol promotes the metal carbonylation, inhibiting the full coordination of H3L. Complex Ir(κ6-fac-C,C',C″-fac-N,N',N″-L) is a phosphorescent emitter upon photoexcitation, which has been employed to fabricate four yellow emitting devices with 1931 CIE (x:y) ∼ (0.52:0.48) and a maximum wavelength at 576 nm. These devices display luminous efficacies, external quantum efficiencies, and power efficacies at 600 cd m-2, which lie in the ranges 21.4-31.3 cd A-1, 7.8-11.3%, and 10.2-14.1 lm W1-, respectively, depending on the device configuration.

Determining the proton diffusion coefficient in highly hydrated iridium oxide films by energy dispersive X-ray absorption spectroscopy

Charge transfer reactions in electrodeposited iridium oxide films (EIROF) are investigated by means of operando energy dispersive X-ray absorption spectroscopy (EDXAS), where oxidation and reduction conditions are selected to drive the Ir(III)/Ir(IV) and Ir(IV)/Ir(V) reactions in acidic solutions. The Ir(III)/Ir(IV) couple is related to a well-known electrochromic phenomenon, while the Ir(IV)/Ir(V) couple might play an important role in the catalysis of the oxygen evolution reactions (OER). In the experiments, current intensity and time-resolved X-ray absorption spectroscopy (XAS) are simultaneously recorded upon application of appropriate potential steps, leading to the independent determination of both the relevant reaction rates and the rate-determining steps. This is allowed by the fast acquisition time (∼10−2 s) at the ESRF Energy Dispersive XAS (EDXAS) ID24 beam-line, in combination with the highly hydrated amorphous iridium oxide electrode material, which in turn allows to maximize the fraction of Ir sites participating in the electrochemical processes. If the experimental conditions exclude the possibility of having either oxygen evolution (or reduction), the Degree of Reaction (DoR), determined by both electrochemistry and XAS, exhibits exponential time dependence, clearly pointing to diffusion-controlled processes. Vice versa, under concomitant OER + oxidation of iridium centers or ORR + iridium reduction, the electrochemical and XAS DoRs highlight different phenomena, providing fully complementary information of the ongoing electrode reactions. In all cases, data elaboration allows to determine the diffusion coefficient of H+ ions within the catalyst layer, that is compared and confirmed by data obtained by electrochemical impedance spectroscopy (EIS). The high values of D obtained for EIROF is compared to values obtained on other IrO2 materials can help in explaining the relevant high electrocatalytic activity.

Unexpected reactivity of cyclometalated iridium(III) dimers. Direct synthesis of a mononuclear luminescent complex.

A new synthetic method has been developed for the preparation of unexpected emissive iridium(III) complexes (A and B), directly obtained from the established [Ir(ppy)2(μ-Cl)]2 dimer, under reaction conditions in which such compounds are usually considered stable. Complex A ([Ir(ppy)2(Oppy)], where Hppy = 2-phenylpyridine and HOppy = 2-(o-hydroxyphenyl)pyridine) was obtained from the dimer without the addition of further ancillary ligands in the reaction environment, but in the presence of a basic water environment in 2-ethoxyethanol as solvent at 165 °C. The complex evidences the unexpected insertion of an oxygen atom between the iridium(III) center and the carbon atom of one ppy moiety. Under specific reaction conditions, the mer-[Ir(ppy)3] complex (B) was obtained. The presence of the right amount of water is important to maximize the formation of A relative to B. Both compounds were fully characterized by NMR spectroscopy and mass spectrometry (MS), and the X-ray structure of A was also determined. DFT calculations were used to shed light on the reaction mechanism leading to the unexpected formation of A, suggesting that the Oppy ligand is generated intramolecularly once the [Ir(ppy)2(μ-OH)]2 dimer is formed. The process is probably assisted by a redox reaction involving the second iridium(III) center in the dimer. The electrochemical and photophysical properties of complexes A and B were investigated in comparison with the well-known fac-[Ir(ppy)3] analogue (C). Complex A displays a green emission (λmax = 545 nm) with a photoluminescence quantum yield (PLQY) of nearly 40%, whereas the oxygen-free counterpart B is poorly emissive, exhibiting an orange emission (λmax = 605 nm) with a PLQY below 10%. These findings may pave the way for the direct synthesis of neutral luminescent complexes with the general formula [Ir(C^N)2(OC^N)], even using dimers with non-commercial or highly substituted C^N ligands, without the need for synthesizing the corresponding hydroxyl-substituted ancillary ligand, which may be hardly obtainable.

Two novel metal-organic frameworks functionalised with pentamethylcyclopentadienyl iridium(III) chloride for catalytic conversion of carbon dioxide to formate.

Hydrogenation of CO2 to formate is a vital reaction, because formate is an excellent hydrogen carrier, which yields blue hydrogen. Blue hydrogen is comparatively cheaper and attractive as the world envisions the hydrogen economy. In this work, two isostructural lanthanide-based MOFs (JMS-6 and JMS-7 [Ln(bpdc)3/2(dmf)2(H2O)2]n) were prepared and used as support materials for molecular catalysts. The bipyridyl MOF backbone were functionalised using pentamethylcyclopentadienyl iridium(III) chloride to give Ir(III)@JMS-6a and Ir(III)@JMS-7a. XPS of the functionalised MOFs show downfield shifts in the N 1s binding energy indicating successful grafting of the complex to the MOF. Hydrogenation experiments in the presence of an organic base showed that the functionalised MOFs were active towards converting CO2 to formate. Ir(III)@JMS-6a and Ir(III)@JMS-7a exhibited the highest turnover numbers of 813 and 621 respectively. ICP-OES indicated insignificant leaching during catalysis. TEM images and XPS data of the recovered catalyst ruled out the presence of Ir(0), confirming that the activity observed was attributed to the molecular Iridium(III) centres.