Iridium Dimer Research Articles

A simple iridium(III) dimer as a switch-on luminescent chemosensor for carbon disulfide detection in water samples

A series of iridium(III) dimers were synthesized and their ability to interact with diethyldithiocarbamate for CS2 sensing was evaluated. Upon the addition of CS2, diethylamine can capture CS2 to form diethyldithiocarbamate, which could chelate with the iridium(III) dimer to form a diethyldithiocarbamate iridium(III) complex, resulting in a yellow luminescence. Dimer 8 exhibited a maximum 18-fold of luminescence enhancement upon the addition of CS2. The luminescence signal of the detection system could be readily distinguished from the highly fluorescent media using time-resolved emission spectroscopy (TRES). The capability of the system to determine CS2 level in water samples was also demonstrated.

Highly efficient phosphorescence from cyclometallated iridium(III) compounds: Improved syntheses of picolinate complexes and quantum chemical studies of their electronic structures

We report a new method to make heteroleptic cyclometallated iridium(III) complexes that employs 1,2-dimethoxyethane (DME) instead of the commonly used 2-ethoxyethanol for the addition of ancillary ligands to chloro-bridged dimeric iridium species. Thus, picolinic acid was quickly and cleanly added to [(F2ppy)2Ir(Cl)]2 (where F2ppy = 2-(4′,6′-difluorophenyl)pyridinato) with base under DME reflux to afford (F2ppy)2Ir(picolinate) (FIrpic) in excellent yield. The high purity of the products obviates the need for further purification, an improvement over the common route in which column chromatography is required. We prepared eleven picolinate complexes by this route, eight of which were characterized by single crystal x-ray diffraction. The complexes possess the same distorted octahedral geometry with two bidentate phenylpyridine ligands and one bidentate 2-picolinate ligand. All of the compounds exhibited efficient phosphorescence with colors ranging from blue to orange; photophysical measurements revealed emission quantum yields as high as 0.92, while most surpassed 0.5. Time-dependent density functional theory calculations, coupled with the use of natural transition orbitals (NTOs), allowed a detailed interpretation of the electronic structures for the complexes. The nature of the acceptor orbital for the lowest-energy triplet state NTO was found to be an important predictor for the emission spectra of FIrpic and its congeners.

Synthesis, biological evaluation and colorimetric sensing studies of platinum group metal complexes comprising pyrazine based thiourea derivatives

A series of complexes (1–9) were synthesized by the reaction of halide bridged metal precursors with the three pyrazine thiourea ligands L1, L2 and L3 to yield cationic as well as neutral complexes and characterized by various spectroscopic techniques. The cationic complexes are represented by the general formula [(arene)M(L)Cl] +, where L = L1, L2 and L3, arene = p-cymene, Cp* and M = Ru, Rh and Ir. All the cationic complexes were isolated with chloride/PF6 as the counter ion. Reactions of rhodium and iridium dimers with L2 yielded neutral complexes 5 and 6 with the general formula [(arene)M(L)Cl2]. The neutral complexes 5 and 6 were further reacted with NaN3 to yield azido complexes 10 and 11. These complexes were, in turn, reacted with acetylene derivatives to yield triazolo complexes 12–15 where only a few triazolo complexes of Cp* have been reported. X-ray diffraction studies revealed the complexes having a typical piano stool geometry around the metal center with the thiourea adducts binding to the metal center in a chelating (N, S) manner. Furthermore, the complexes 1–9, as well as the ligands were screened for potential anti-bacterial agents out of which complexes 3 and 5 exhibited anti-bacterial activity. Colorimetric sensing studies showed the agglomeration of the silver NPs upon addition of the ligands while the complexes were unresponsive.

Synthesis of 2‐Arylquinolines from 2‐Iodoanilines and β‐Chloropropiophenones via Palladium‐Catalyzed Cascade Reaction

AbstractA protocol to access 2‐aryl‐substituted quinolines from readily available 2‐iodoanilines and β‐chloropropiophenones, which are synthetic equivalents of acrylophenones, has been developed via the palladium‐catalyzed cascade reaction. Various 2‐iodoanilines and β‐chloropropiophenones were applicable to this protocol to afford the desired quinoline products in good to high yields. Moreover, we demonstrated the usefulness of this protocol in direct synthesis of chloride‐bridged dimeric iridium complexes, one of the key intermediates in the synthesis of iridium‐based phosphorous materials, without the complete isolation of the quinolines.

Electrochemiluminescence energy transfer in mixed iridium-based redox copolymers immobilised as nanoparticles

Energy transfer in a redox metallopolymer containing both fluorinated and non-fluorinated cyclometalated iridium (II) centres is explored. These materials are readily prepared by mixing two different iridium dimers and a backbone chain containing pendant groups (e.g. poly-vinylpyridine/poly-styrene), which can coordinate to the metal centres. Their easy synthesis together with their ability to self-assemble into polymeric nanoparticles in aqueous media render them a unique emitting material with nanoscale dimensions. We report the photophysical, electrochemical and electrochemiluminescence (ECL) properties of these polymeric nanoparticles in solution and immobilised as a thin layer. We demonstrate Dexter-type Energy Transfer (ET) and ECL-ET phenomena resulting in ECL enhancement by up to 505% compared with metallopolymers containing only one type of iridium centre. These results demonstrate the possibility of synthesising new materials with tailored and enhanced emission wavelengths by careful selection of the emitting centres for any opto-electronic and sensing-related applications.

Large magnetic anisotropy in chemically engineered iridium dimer

Exploring giant magnetic anisotropy in small magnetic nanostructures is of technological merit for information storage. Large magnetic anisotropy energy (MAE) over 50 meV in magnetic nanostructure is desired for practical applications. Here we show the possibility to boost the magnetic anisotropy of the smallest magnetic nanostructure—transition metal dimer. Through systematic first-principles calculations, we proposed an effective way to enhance the MAE of an iridium dimer from 77 meV to 223–294 meV by simply attaching a halogen atom at one end of the Ir–Ir bond. The underlying mechanism for the enormous MAE is attributed to the rearrangement of the molecular orbitals which alters the spin-orbit coupling Hamiltonian and hence the magnetic anisotropy. Our strategy can be generalized to design other magnetic molecules or clusters to obtain giant magnetic anisotropy.

Synthesis of Phenylpyridine Iridium(III) Complexes with N-Heterocyclic Carbene as Ancillary Ligands

In this study, [Ir(2,4-F2ppy)2(2-(1,2,4-triazol-1-yl)pyridine>)]PF6 (C1), [Ir(2,4-F2ppy)2(2-(2-(4-dimethylbenzyl)-1,2,4-triazol-1-yl)pyridine)]PF6 (C2) and [Ir(2,4-F2ppy)2(2(2-hexyl-1,2,4-triazol-1-yl)pyridine)]PF6 (C3) complexes were successfully synthesised by refluxing the mixture of dichloro-bridged iridium(III) dimer, [Ir(2,4-F2ppy)2(μ-Cl)]2 and corresponding triazolium salt containing N-heterocyclic carbene (NHC) as ancillary ligands. 1H NMR of all complexes display well-resolved signals between 10.00-5.00 ppm assign to proton at the aromatic region for penylpyridine and pyridyltriazole. Spectra of C2 and C3 also display signals at aliphatic region (singlets) between 0.80-1.50 ppm that proved the presence of methylbenzyl and hexyl substituent on the pyridyltriazole ring. In addition, IR analysis reported the presence of C=C and C=N stretching of pyridine at range 1570-1470cm−1 and C-H stretching of aromatic pyridine at 2990-3080cm−1. Besides, UV-Vis absorption data showed that the low-energy metal-to-ligand charge-transfer (MLCT) band in C2 (364 nm) is significantly blue-shifted compared to C1 (375 nm) and C3 (381 nm). Overall, this study reported the synthesis and spectroscopic study of phenylpyridine Ir(III) complexes with various types of pyridyltriazole (NHC ancillary ligands).

Incorporation of Monatomic Cations onto an Ir–Ir Bond in a Dimeric Iridium(II) Complex Having a 1,3-Diene-1,4-diyl Backbone

A dinuclear iridium(II) complex with 1,3-butadiene-1,4-diyl backbone and iridium–iridium bonding interaction has been found from the complexation of an iridium(I) precursor and an alkyne-containing bisphosphine ligand. This complex shows binding ability toward a variety of cations such as Ag+, I+, H+ to afford merged cationic diiridium complexes. Structural differences and electronic features of iridium–iridium bonding are discussed using X-ray crystallographic analyses as well as in silico studies with density functional theory.

Emission Tuning of Ir(N∧C)2(pic)-Based Complexes via Torsional Twisting of Picolinate Substituents

Pyridine-2-carboxylate (pic) has been employed extensively as a blue-shifting ancillary ligand in the production of cyclometalated iridium complexes used in OLEDs, but surprisingly, further elaboration of this ligand has largely been unexplored. In this work we demonstrate a simple and versatile route for modifying picolinate ligands coordinated to iridium. Reacting a μ-chloro iridium(C∧N) dimer (where C∧N is a phenylpyridine-based ligand) with 4-bromopicolinic acid (HpicBr) yields the corresponding iridium(C∧N)2(picBr) complexes, which were readily modified by a Suzuki–Miyaura reaction to give the corresponding aryl-substituted picolinate complexes. The luminescent behavior of these complexes shows that by restricting the torsional angle between the substituent and pic the emission can be shifted by up to 77 nm.

BODIPY-based Ir(III) rectangles containing bis-benzimidazole ligands with highly selective toxicity obtained through self-assembly

Selectivity for cancerous cells over normal cells remains one of the most important issues in studies of the biological activities of metal-based drugs. Herein, we show that benzimidazole-based iridium BODIPY rectangles can be used to selectively kill cancer cells. New tetranuclear (2 + 2) metalla-rectangles 1 and 2 were synthesized through the self-assembly of benzimidazole and BODIPY ligands with dichloro (pentamethylcyclopentadienyl) iridium dimer. The new complexes were fully characterized using different analytical techniques and a single-crystal structure was obtained for rectangle 2. Cytotoxicity studies revealed that complex 1 is highly selective for cervical cancer cells (HeLa) and human glioblastoma (U87) cancer cells over non-malignant lung fibroblast cells (WI38). The selectivity of complex 1 is much superior than that of well-known drug cisplatin. The cellular uptake and intracellular localization of these complexes were examined through confocal microscopy studies, and complex 1 was found to localize primarily in the cytoplasmic region of cancer cells. Furthermore, the interactions of these complexes with biomolecules in solution were investigated through spectroscopic studies.

The Discovery of an Iridium(III) Dimer Complex as a Potent Antibacterial Agent against Non-Replicating Mycobacterium smegmatis.

Novel agents are urgently needed to rapidly kill drug-resistant Mycobacterium tuberculosis. Noble metal complexes, particularly polypyridyl iridium complexes serving as therapeutic agents, have attracted considerable interest recently, due to their significant cytotoxic or antimicrobial activities. Here, we reported an polypyridyl iridium dimer complex [Ir(ppy)2Cl]2 (3), with ppy = phenylpyridine, which was found to be active against both exponential growing and non-replicating M. smegmatis, with minimum inhibitory concentration values of 2 μg/mL, and exhibited rapid bactericidal kinetics, killing pathogens within 30–60 min. Moreover, 3 was demonstrated to generate a large amount of reactive oxygen species and to be effective in drug-resistant strains. Taken together, the selectively active iridium(III) dimer complex showed promise for use as a novel drug candidate for the treatment of M. tuberculosis infection.

Conformational twisting of a formate-bridged diiridium complex enables catalytic formic acid dehydrogenation.

We previously reported that iridium complex 1a enables the first homogeneous catalytic dehydrogenation of neat formic acid and enjoys unusual stability through millions of turnovers. Binuclear iridium hydride species 5a, which features a provocative C2-symmetric geometry, was isolated from the reaction as a catalyst resting state. By synthesizing and carefully examining the catalytic initiation of a series of analogues to 1a, we establish here a strong correlation between the formation of C2-twisted iridium dimers analogous to 5a and the reactivity of formic acid dehydrogenation: an efficient C2 twist appears unique to 1a and essential to catalytic reactivity.

Redox Activity of Oxo-Bridged Iridium Dimers in an N,O-Donor Environment: Characterization of Remarkably Stable Ir(IV,V) Complexes.

Chemical and electrochemical oxidation or reduction of our recently reported Ir(IV,IV) mono-μ-oxo dimers results in the formation of fully characterized Ir(IV,V) and Ir(III,III) complexes. The Ir(IV,V) dimers are unprecedented and exhibit remarkable stability under ambient conditions. This stability and modest reduction potential of 0.99 V vs NHE is in part attributed to complete charge delocalization across both Ir centers. Trends in crystallographic bond lengths and angles shed light on the structural changes accompanying oxidation and reduction. The similarity of these mono-μ-oxo dimers to our Ir "blue solution" water-oxidation catalyst gives insight into potential reactive intermediates of this structurally elusive catalyst. Additionally, a highly reactive material, proposed to be a Ir(V,V) μ-oxo species, is formed on electrochemical oxidation of the Ir(IV,V) complex in organic solvents at 1.9 V vs NHE. Spectroelectrochemistry shows reversible conversion between the Ir(IV,V) and proposed Ir(V,V) species without any degradation, highlighting the exceptional oxidation resistance of the 2-(2-pyridinyl)-2-propanolate (pyalk) ligand and robustness of these dimers. The Ir(III,III), Ir(IV,IV) and Ir(IV,V) redox states have been computationally studied both with DFT and multiconfigurational calculations. The calculations support the stability of these complexes and provide further insight into their electronic structures.

Exploring the Chemistry and Photophysics of Substituted Picolinates Positional Isomers in Iridium(III) Bisphenylpyridine Complexes

A simple and versatile route for modifying picolinate ligands coordinated to iridium is described. Reacting a μ-chloro iridium(C∧N) dimer (where C∧N is a phenylpyridine-based ligand) with bromopicolinic acid (HpicBr) yields the corresponding iridium(C∧N)2(picBr) complexes (1–4 and 11), which were readily modified by a Sonogashira reaction to give eight alkyne-substituted picolinate complexes (5–10, 12, and 13). The luminescent behavior of these complexes shows that the position of substitution about the picolinate ring has an effect on both photophysical behavior as well as the reactivity.

One‐Pot N‐Deprotection and Catalytic Intramolecular Asymmetric Reductive Amination for the Synthesis of Tetrahydroisoquinolines

AbstractA one‐pot N‐Boc deprotection and catalytic intramolecular reductive amination protocol for the preparation of enantiomerically pure tetrahydroisoquinoline alkaloids is described. The iodine‐bridged dimeric iridium complexes displayed superb stereoselectivity to give tetrahydroisoquinolines, including several key pharmaceutical drug intermediates, in excellent yields under mild reaction conditions. Three additives played important roles in this reaction: Titanium(IV) isopropoxide and molecular iodine accelerated the transformation of the intermediate imine to the tetrahydroisoquinoline product; p‐toluenesulfonic acid contributed to the stereocontrol.

One-Pot N-Deprotection and Catalytic Intramolecular Asymmetric Reductive Amination for the Synthesis of Tetrahydroisoquinolines.

A one-pot N-Boc deprotection and catalytic intramolecular reductive amination protocol for the preparation of enantiomerically pure tetrahydroisoquinoline alkaloids is described. The iodine-bridged dimeric iridium complexes displayed superb stereoselectivity to give tetrahydroisoquinolines, including several key pharmaceutical drug intermediates, in excellent yields under mild reaction conditions. Three additives played important roles in this reaction: Titanium(IV) isopropoxide and molecular iodine accelerated the transformation of the intermediate imine to the tetrahydroisoquinoline product; p-toluenesulfonic acid contributed to the stereocontrol.

Hydrogen Isotope Exchange with Iridium(I) Complexes Supported by Phosphine‐Imidazolin‐2‐imine P,N Ligands

AbstractPhenylene‐bridged hybrid phosphine‐imidazolin‐2‐imine RP,NR′ ligands (R=Ph, Cy, i‐Pr, t‐Bu; R′=Me, i‐Pr) were prepared from 1,2‐dibromobenzene by palladium‐catalyzed C–N coupling with 1,3,4,5‐tetramethylimidazolin‐2‐imine or 1,3‐diisopropyl‐4,5‐dimethylimidazolin‐2‐imine, followed by lithiation with tert‐butyllithium and reaction with the chlorophosphines (R2PCl). Their reaction with the dimeric iridium complex [Ir(cod)Cl]2 (cod=1,5‐cyclooctadiene) and subsequent anion exchange with sodium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (NaBArF24) or potassium hexafluorophosphate (KPF6) afforded iridium complexes of the type [(RP,NR′)Ir(cod)]BArF24 or [(RP,NR′)Ir(cod)]PF6, respectively. The latter PF6 salts were structurally characterized, revealing short Ir—N bonds as an indication of electron‐rich nitrogen donor atoms. The former complexes were tested for their applicability in catalytic H/D exchange. In particular, the complex with the ligand t‐BuP,NMe showed remarkable performance in H/D exchange with a broad range of aromatic substrates, including ketones, amides, esters, heterocycles and nitro compounds, and also promoted H/D exchange at aromatic Boc‐protected amines, benzylamines and methoxy derivatives.magnified image

Rapid Access to Derivatized, Dimeric, Ring-Substituted Dichloro(cyclopentadienyl)rhodium(III) and Iridium(III) Complexes

The present work describes the design and synthesis of a series of rhodium and iridium dimers [(η5-ring)MCl]2(μ2-Cl)2 (where (η5-ring)MCl = (η5-Me4C5R)Rh(III)Cl or (η5-Me4C5R)Ir(III)Cl) using a new and efficient 1 h procedure. Rhodium and iridium dimeric complexes were synthesized via a microwave reaction. The modified HMe4C5R (R = isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, phenyl, benzyl, phenethyl, cyclohexyl, and cyclopentyl) type ligands were synthesized by reaction of 2,3,4,5-tetramethylcyclopent-2-en-1-one with the respective Grignard reagent (RMgX), followed by elimination of water under acidic conditions to produce the tetramethyl(alkyl or aryl)cyclopentadienes in moderate to excellent yields (40–98%). Reaction of the HMe4C5R ligands with [M(COD)](μ2-Cl)2 (M = Rh, Ir; COD = 1,5-cyclooctadiene) gave the dimeric complexes [(η5-Me4C5R)MCl]2(μ2-Cl)2 in yields ranging from 47% to 96%. The derivatized dimers were tested for antimicrobial activity, showing activity aga...

Iridium (III) 1,3-bis(aryl)triazenide complexes: Synthesis, characterization and structure

Iridium (III) 1,3-bis(aryl)triazenide complexes [Cp∗IrCl(ArNNNAr′)] (Cp∗=C5Me5, Ar=Ar′=C6H5, 1; Ar=Ar′=o-CF3-C6H4, 2; Ar=Ar′=o-HOCH2-C6H4, 3; Ar=o-HOCH2-C6H4, Ar′=p-CH3-C6H4, 4) have been obtained by reaction of iridium dimer [Cp∗IrCl2]2 with the corresponding triazenes in the presence of NEt3 in CH3CN. The iridium complexes 1–4 were characterized by IR, ESI-MS and NMR spectroscopy. In all of the complexes, the triazenes are coordinated to iridium (III) as monoanionic bidentate N,N′-donor ligands. Compounds 1–4 are the first examples studied by single crystal X-ray diffraction of mononuclear bis(aryl)triazenide iridium complexes, where the N-N-N fragment effectively chelates the Ir (III) central atom.

Enantioselective hydrogenation of ketones by iridium nanoparticles ligated with chiral secondary phosphine oxides

Chiral iridium nanoparticles (IrNPs) were synthesized by H2reduction of (1,5-cyclooctadiene)(methoxy)iridium(i) dimer ([Ir(OMe)(COD)]2) in the presence of an asymmetric secondary phosphine oxide.