Chloro-bridged Dimer Research Articles

(2-[4-Methylpyrazol-1-yl]phenyl)platinum(II) (1,3-bis[1-methyl-1H-pyrazol-4-yl]propane-1,3-dione)

In this work, the title compound was synthesized via the reaction of an aryl-substituted pyrazole with potassium tetrachloroplatinate, followed by the reaction of the postulated intermediate chloro-bridged dimer with a pyrazole-containing 1,3-diketonate ligand. The structure of the synthesized complex was established by 1H, 13C NMR spectroscopy and mass spectrometry. According to UV-Vis spectrometry studies, the obtained complex exhibits green fluorescence with a maximum at 514 nm. Based on cyclic voltammetry studies, the HOMO, LUMO and band gap values were calculated.

Iridium(III) complexes based on cyanomethane and cyanamide ligands with luminescence quenching properties for Fe(III) sensing and biological activities

Two organometallic iridium(III) complexes, Ir(ppy)2Cl(NCCH3) (1) and Ir(ppy)2Cl(NCNH2) (2), were accidentally synthesized from the reaction between the chloro-bridged dimer of (ppy)2Ir(μ-Cl)2Ir(ppy)2 and 2-aminobenzothiazole (abt, C7H6N2S) ligand refluxed in dichloromethane under Ar gas. In the obtained complexes, ppy is 2-phenylpyridine, NCCH3 is cyanomethane or acetonitrile, and NCNH2 is the cyanamide ligand. Complex 1 was received instead of the expected Ir(ppy)2Cl(abt) complex, after the reaction completed for 10 h. Acetonitrile entered as a ligand to the coordination sphere of Ir(III) during the precipitation stage. The reaction was repeated, refluxing for 20 h. This time, the abt ligand fragmented into the cyanamide molecule yielding complex 2 instead of the Ir(ppy)2Cl(abt) complex. Single-crystal X-ray analysis revealed the distorted octahedral geometries of both title complexes. The N and C donors of ppy were in their typical trans- and cis- orientations, respectively. The cyanomethane and cyanamide ligands coordinated via the N-atom. Both complexes exhibited similar photo-physical properties. Complexes 1 and 2 emitted green luminescence between 520 and 525 nm when excited with 325 and 350 nm, respectively, at room temperature in dichloromethane. The respective relative quantum efficiencies were 0.06 and 0.08, compared to coumarin 6 in ethanol. The luminescent emission of both complexes was selectively turn-offtoward increasing Fe3+ concentrations. The 1:1 binding stoichiometry between the complex and Fe3+ ion was determined by Job's plot. Benesi-Hildebrand plots were applied to determine the binding constants (Kb) of 5.86 × 104 and 9.50 × 104 M−1 for complexes 1 and 2, respectively. The complex 2 displayed in vitro cytotoxicity toward HCC1937 and MDA-MB-231 human breast cancer cells with IC50 values of 13.5 and 72.8 µM, respectively. These values indicated 2–3 folds higher sensitivity than cisplatin. In addition, complex 1 showed inhibitory activity against the Gram-positive bacteria Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA), with MIC/MBC values of 32/32 and 32/64 μg. mL−1, respectively.

Cleavage of the dimeric heterometallic complexes [Pd(dppf)(μ-Cl)]2[BArF24]2 (dppf = 1,1′-bis(diphenylphosphino)ferrocene, BArF24 = tetrakis(bis-3,5-trifluoromethylphenyl)borate) via addition of monodentate phosphine ligands

The cleavage of the heterometallic, chloro-bridged dimer [Pd2(dppf)2(µ-Cl)2][BArF24]2 (dppf = 1,1′-bis(diphenylphosphino)ferrocene; BArF24 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) was of interest within this study. The addition of the monodentate phosphines, PPh3, PMe3 and diphenylferrocenylphosphine (PPh2Fc), resulted in the formation of three new [Pd(dppf)(PR3)Cl][BArF24] complexes. These new compounds were characterized by NMR and the X-ray crystal structures of all three compounds were obtained. Structural parameters for these compounds were compared to other square-planar Pd(II) compounds with a dppf ligand. In addition, the oxidative electrochemistry of these three compounds was examined using cyclic voltammetry and the electronic communication between the two different iron centers in [Pd(dppf)(PPh2Fc)Cl][BArF24] was explored.

Investigating the antiplasmodial activity of substituted cyclopentadienyl rhodium and iridium complexes of 2-(2-pyridyl)benzimidazole

Six cationic half-sandwich Ir(III) and Rh(III) complexes (C1-C6) were synthesised by reaction of 2-(2-pyridyl)benzimidazole with the appropriate chloro-bridged dimers. All complexes were fully characterised using standard spectroscopic techniques and their purity confirmed by RP-HPLC. The molecular structures of these complexes were elucidated using single-crystal X-ray diffraction. Depending on the substituted cyclopentadienyl (Cpx) ligands, the complexes crystallized with an orthorhombic (Cpx = pentamethylcyclopentadienyl), monoclinic (Cpx = tetramethylphenylcyclopentadienyl) or triclinic (Cpx = tetramethylbiphenylcyclopentadienyl) crystal system. All complexes displayed good solubility in PBS and HEPES buffers within the concentration range used for the in vitro inhibitory screening. Using proton NMR experiments, the stability of the complexes in water was monitored at 37 °C and all complexes were resistant to displacement of their chlorido ancillary ligands by water. In vitro screening against the 3D7 chloroquine-sensitive and Dd2 multi-drug-resistant strains of Plasmodium falciparum revealed all complexes exhibited moderate to good potency. Complex C6 emerged as the most promising candidate with IC50 values of 0.75 ± 0.11 and 0.42 ± 0.055 µM against the 3D7 and Dd2 strains, respectively. The newly synthesised complexes were not cytotoxic to Human Embryonic Kidney cells.

Mild intramolecular P–C(sp3) bond cleavage in bridging diphosphine complexes of RuII RhIII and IrIII

Three new carboxylic acid functionalised diphosphines, R2PCH2N(Ar)CH2PR2 [CyL1 R = Cy, Ar = (1-CO2H)(3-OMe)C6H3, CyL2 R = Cy, Ar = (1-CO2H)(3-OH)C6H3 and PhL3 R = Ph, Ar = (1-CO2H)(5-OMe)C6H3] have been prepared from condensation of R2PCH2OH and the appropriate aromatic amine in MeOH, and isolated as colourless solids (for CyL1, CyL2) in good yield. Reaction of CyL1, CyL2, or PhL3, along with the previously reported diphosphines PhL1, PhL2, and PhL4, and [RuCl(μ-Cl)(η6-Me2CHC6H4Me)]2 in CH2Cl2 affords the P/P-bridging dinuclear ruthenium(II) complexes {RuCl2(η6-Me2CHC6H4Me)}2(μ-CyL1−PhL4) 1a−f as red/orange solids. Careful monitoring by 31P{1H} NMR spectroscopy of CDCl3 solutions of 1a−e revealed remarkably clean P−Csp3 bond cleavage to give RuII mononuclear species 2a−e and the known secondary phosphine complexes RuCl2(η6-Me2CHC6H4Me)(PCy2H) 3 and RuCl2(η6-Me2CHC6H4Me)(PPh2H) 4. Furthermore, facile P−Csp3 bond cleavage of PhL1 can be observed using the chloro-bridged dimers [IrCl(μ-Cl)(η5-C5Me5)]2 or [RhCl(μ-Cl)(η5-C5Me5)]2 instead. Deuterium labelling of CyL1, CyL1, PhL1, and PhL2 enabled the assignment of the methylene protons to be confirmed from 1H NMR spectroscopy. All new compounds have been characterised using a range of spectroscopic and analytical techniques. Single crystal X-ray structures have been determined for CyL1, 1d·3OEt2,1f·2CDCl3·OEt2, 2b, 2c, 2d·CDCl3, 2e·0.5OEt2 and 6b·1.5CDCl3. The free phenolic group in CyL1, 1d·3OEt2,1f·2CDCl3·OEt2, 2b and 2d·CDCl3 participates in intra- or intermolecular O−H···O hydrogen bonding.

Microwave-Accelerated C,N-Cyclometalation as a Route to Chloro-Bridged Iridium(III) Binuclear Precursors of Phosphorescent Materials: Optimization, Synthesis, and Studies of the Iridium(III) Dimer Behavior in Coordinating Solvents.

We present the results of our research on the use of microwaves as an unconventional heat source for the acceleration of iridium(III) chloro-bridged dimer preparation. The results enabled us to revise and improve known guidelines for the very quick and highly efficient synthesis of iridium(III) dimeric complexes in a very simple isolation manner. According to the developed methodology, the already known dimers containing ligands based on the 2-phenylpyridinato motif, as well as new ones stabilized with functionalized benzo[h]quinolinato and 2-phenoxypyridinato-based ligands, were efficiently synthesized. The scope of the incorporated ligands included compounds equipped with electron-donating (-Me, -OMe, -OPh, -NMe2), electron-withdrawing (-F, -Br, -CF3, -C6F5), and hole-transporting (-NPh2, -C6H4NPh2) groups. The obtained complexes were characterized by NMR, X-ray diffraction, and electrospray ionization mass spectrometry methods, and their behavior was examined in the presence of coordinating solvents such as dimethyl sulfoxide and acetonitrile. Investigation of the interactions between the above-mentioned solvents and dimers enabled us to confirm the ability of the former to cleave μ-chloride bridges, which enriches the knowledge in the field of organometallic chemistry. This knowledge can be particularly useful for the scientists working in the field of iridium-based materials, helping to avoid misinterpretation of the spectroscopic data.

Synthesis, molecular structure and antioxidant activity of bis [L(μ2-chloro)copper(II)] supported by phenoxy/naphthoxy–imine ligands

A new series of Cu(II) complexes [bis[{(μ2-chloro)-2-MeO-Ph-CH2-(N=CH)-2,4-tert-butyl-2-OC6H2)}Cu(II)] (Cu1); bis[{(μ2-chloro)-2-MeS-Ph-CH2-(N=CH)-2,4-tert-butyl-2-(OC6H2)}Cu(II)] (Cu2); bis[{(μ2-chloro)-2-MeO-Ph-CH2-(N=CH)-2-(OC10H6)} Cu(II)] (Cu3); bis[{(μ2-chloro)-2-MeS-Ph-CH2-(N=CH)-2-(OC10H6)}Cu(II)] complex (Cu4); bis[{2-MeS-Ph-CH2-(N=CH)-2,4-tert-butyl-2-(OC6H2)}Cu(II)] (Cu5)] have been synthesized and characterized by elemental analysis, IR, UV–Visible and by X-ray crystallography for Cu1, Cu4 and Cu5. In the solid state, Cu1 features of a chloro-bridged dimer complex with κ2 coordination of the monoanionic phenoxy-imine ligand onto the copper center. On the other hand, the molecular structure of Cu4 reveals the naphthoxy-imine ligand with pendant S-group coordinated to the copper atom in tridentate meridional fashion. Treatment of [Cu(OAc)2·H2O] with two equiv. of [2-MeS-Ph-CH2-(N=CH)-2,4-tert-butyl-2-(HOC6H2)] led to a monomeric complex Cu5, with the ONS-donor Schiff base acting as a bidentate ligand. The redox behavior was explored by cyclic voltammetry. The reduction/oxidation potential of Cu(II) complexes depends on the structure and conformation of the central atom in the coordination compounds. Antioxidant activities of the complexes, Cu1 - Cu5, were determined by in vitro assays such as 1,1-diphenyl-2-picryl-hydrazyl free radicals (DPPH) and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radicals (ABTS+). The dinuclear compounds Cu1-Cu4, from the concentration of 5 μM, presented a good activity in scavenging DPPH radical. In addition, most of the Cu(II) complexes showed ABTS.+ radical-scavenging activity. The monomeric complex Cu5 at all concentrations tested showed antioxidant inability. The cytotoxicity of the Cu1 and Cu3 was determined in V79 cell line by reduction of 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay.

Two new phosphorescent Ir(III) complexes as efficient selective sensors for the Cu2+ ion

Two new cationic iridium(III) complexes were successfully synthesized as highly sensitive and selective phosphorescent sensors for detection of Cu2+ in MeOH/H2O (1:1) solution and in living cells. These cationic Ir(III) complexes were prepared by reactions of two different Ir(III) chloro-bridged dimers with 2,2′-dipyridine tethered DPA (di(2-picolyl)amine) moiety as the ancillary ligand. These phosphorescent sensors displayed significant reversible phosphorescence quenching upon binding to Cu2+ ions with a 10 ppb detection limit. They had strong binding ability with Cu2+ ions and the binding ratios were approximately 1:1, and also exhibited good cell permeability and good imaging characteristics in detecting Cu2+ ions in living cells. It is worth mentioning that one of the phosphorescent sensors is almost nontoxic to Hela cells, indicating that it greatly increases the possibility of application in biochemistry.

Influences of Fluorine Substituents on Iminopyridine Fe(II)- and Co(II)-Catalyzed Isoprene Polymerization.

A series of iminopyridine complexes of Fe(II) and Co(II) complexes bearing fluorinated aryl substituents were synthesized for the polymerization of isoprene. The structures of complexes 3a, 2b and 3b were determined by X-ray diffraction analysis. Complex 3a contained two iminopyridine ligands coordinated to the iron metal center forming an octahedral geometry, whereas 2b adopted a chloro-bridged dimer, and 3b featured with two patterns of cobalt centers bridged via chlorine atoms. Complexes 2b and 3b represented rare examples of chlorine bridged bimetallic Co(II) complexes. The fluorine substituents effects, particularly on catalytic activity and polymer properties such as molecular weight and regio-/stereo-selectivity were investigated when these complexes were employed for isoprene polymerization. Among the Fe(II)/methylaluminoxane (MAO) systems, the 4-CF3 substituted iminopyridine Fe(II) complex 1a was found as a highly active isoprene polymerization catalyst exhibiting the highest activity of 106 g·(mol of Fe)−1·h−1. The resultant polymer displayed lower molecular weight (Mn = 3.5 × 104 g/mol) and moderate polydispersity index (PDI = 2.1). Furthermore, the ratio of cis-1,4-/3,4 was not affected by the F substituents. In the series of Co(II)/AlEt2Cl binary systems, complexes containing electron-withdrawing N-aryl substituents (R = 4-CF3, 2,6-2F) afforded higher molecular weights polyisoprene than that was obtained by the complex containing electron-donating N-alkyl substituents (R = octyl). However, ternary components system, complex/MAO/[Ph3C][B(C6F5)4] resulted in low molecular weight polyisoprene (Mn < 2000) with high trans-1,4-unit (>95%).

Red photo- and electroluminescent half-lantern cyclometalated dinuclear platinum(II) complex

Abstract New cyclometalated dinuclear platinum(II) complex bearing bridged 4,6-dimethylpyrimidine-2(1H)-thiolate (μ-C6H7N2S-κN,S) ligands, [{Pt(ppy)(μ-C6H7N2S-κN,S)}2] (3) (ppy=(2-phenylpyridinato-C2,N)) was prepared via the reaction of chloro-bridged dimer [{Pt(ppy)Cl}2] with 4,6-dimethylpyrimidine-2(1H)-thione (C6H8N2S) in the presence of t-BuOK. The complex holds dinuclear frameworks with short Pt(II)···Pt(II) distance (2.8877(3) Å), and exhibit red intense luminescence from the triplet metal-metal-to-ligand charge-transfer at 697 nm in CH2Cl2 solution and at 649 nm in solid state at RT. Single crystal XRD analysis reveals the metallophilic interactions Pt···Pt with significant covalent contribution in the structure of 3 which were studied by quasi-relativistic and relativistic DFT calculations (viz., M06/MWB60(Pt) and 6-311+G* (other atoms); M06/DZP-DKH levels of theory) and topological analysis of the electron density distribution within the framework of Bader’s theory (QTAIM method). Estimated strength of the Pt···Pt contact is 8.1–12.2 kcal/mol and it is mostly determined by crystal packing effects and weak attractive interactions between the adjacent metal centers due to overlapping of their dz2 and pz orbitals. An organic light-emitting diode based on this complex showed red electroluminescence with maximal luminance of 115 cd/m2 and current efficiency of 2.45 cd/A at this luminance.

Elucidating Zn and Mg Electrodeposition Mechanisms in Nonaqueous Electrolytes for Next-Generation Metal Batteries

Cyclic voltammetry and linear sweep voltammetry with an ultramicroelectrode (UME) were employed to study Zn and Mg electrodeposition and the corresponding mechanistic pathways. CVs obtained at a Pt UME for Zn electroreduction from a trifluoromethylsulfonyl imide (TFSI–) and chloride-containing electrolyte in acetonitrile exhibit current densities that are scan rate independent, as expected for a simple electron transfer at a UME. However, CVs obtained from three different Mg-containing electrolytes in THF exhibit an inverse dependence between scan rate and current density. COMSOL-based simulation suggests that Zn electrodeposition proceeds via a simple one-step, two-electron transfer (E) mechanism. Alternatively, the Mg results are best described by invoking a chemical step prior to electron transfer: a chemical–electrochemical (CE) mechanism. The chemical step exhibits an activation energy of 51 kJ/mol. This chemical step is likely the disproportionation of the chloro-bridged dimer [Mg2(μ–Cl)3·6THF]+ pre...

Half-sandwich d6 metal complexes comprising of 2-substituted-1,8-napthyridine ligands with unexpected bonding modes: Synthesis, structural and anti-cancer studies

The Friedländer condensation reaction between 2-aminonicotinealdehyde and acetophenone derivatives in presence of potassium hydroxide yielded 2-substituted-1,8-napthyridine derivatives viz. 2-(1,8-napthyridin-2-yl)phenol (PHNp), 2-(1,8-napthyridin-2-yl)aniline (AnNp) and 2-(pyridine-4-yl)-1,8-napthyridine (PyNp). Treatment of the chloro-bridged dimers [(arene)MCl2]2 [arene = p-cymene, Cp*; M = Ru, Rh and Ir] with two equivalents of napthyridine ligands (PHNp, AnNp and PyNp) allowed the formation of mononuclear napthyridine complexes having formula [(arene)M(PHNp)Cl2] (1–3), [(arene)M(AnNp)Cl]PF6 (4–6) and [(arene)M(PyNp)Cl2] (7–9). These napthyridine compounds were isolated as neutral and cationic complexes which were further characterized by analytical and spectroscopic techniques. The molecular structures of some of the respective napthyridine complexes were established by carrying out the single crystal X-ray analysis. Single crystal X-ray studies revealed the coordination of the napthyridine ligands to the metal center wherein AnNp ligand coordinated metal in a bidentate chelating NN′ manner and PHNp and PyNp ligand coordinated metal in a monodentate fashion. In case of PHNp complexes the coordination occurs through napthyridine nitrogen N(1) whereas in case of PyNp complexes the coordination takes place through pyridine nitrogen N(1). These napthyridine complexes possessed cytotoxicity against HCT-116 (human colorectal cancer) and MIA-PaCa-2 (pancreatic carcinoma) cancer cell lines as compared to non-cancer cell line ARPE-19.

A new access to tri(1-naphthyl)phosphine and its catalytically active palladacycles and luminescent Cu(I) complex

New approach to synthesis of tri(1-naphthyl)phosphine (Np3P) and its application for design of new Pd(II) and Cu(I) complexes are reported. This phosphine has been prepared in 32% yield through exhaustive P–H arylation of РН3 with 1-chloronaphthalene in the superbasic t-BuOK/DMSO system at 70°C. The Np3P was found to readily reacts with chloro-bridged dimers, [(κ2-C,N)Pd(μ-Cl)]2 (κ2-C,N=PhCH2NMe2 (2a) or FcCH2NMe2 (2b), to give new mononuclear palladacycles [(κ2-C,N)Pd(Np3P)Cl] (3, 4), in which metal has a square-planar geometry. These complexes show good catalytic activity in the Sonogashira reaction under low catalyst loadings (2mol% Pd) and relatively mild conditions. We also synthesized and characterized first Cu(I) complex with Np3P, namely, [Cu(phen)(Np3P)I], that exhibits red emission (λmax=650nm) at room temperature.

Halogen and chalcogen bonding in dichloromethane solvate of cyclometalated iridium(III) isocyanide complex

Abstract Solvent-rich dichloromethane solvate of cis-[Ir(bptz)2(CNXyl)2]BF4 (3, bptz is cyclometallated 4-(4-bromophenyl)-2-methylthiazole) is prepared via the reaction of chloro-bridged dimer [Ir(bptz)2(μ-Cl)]2 (1) with 2,6-dimethylphenyl isocyanide (CNXyl, 2) and AgBF4. Single crystal X-ray diffraction on the 3·3¼CH2Cl2 solvate showed the presence of numerous non-covalent interactions, including the C–S···F–B chalogen bonding (ChB), the C–Br···Br–C, C–Cl···Br–C, and C–Cl···S(C)–C halogen bonding (XB), and the C–H···F–B hydrogen bonding (HB). The nature of these short contacts was explored both experimentally by single-crystal X-ray diffraction and theoretically by DFT calculations on the empirical geometries followed by Bader’s topological electron density distribution analysis. The evaluated energies of XBs and ChBs are in range 1.3–2.2 kcal/mol indicating the non-covalent nature of the contacts.

First cyclometallated Pd(II) diselenophosphinate: Synthesis, structural and theoretical investigation

First cyclometallated PdII diselenophosphinate, namely [(dmba)Pd(Se2PPh2)] (dmba = PhCH2NMe2), has been synthesized in 72% yield by reaction of chloro-bridged dimer, [(dmba)Pd(μ-Cl)]2 (dmba = PhCH2NMe2), with sodium diselenophosphinate, Na[Se2PPh2]. This complex has been characterized by X-ray crystallography (XRD), NMR (1H and 31P), FT-IR, UV–Vis and ESI-MS techniques. The XRD analysis reveals that the Pd atom has a square-planar geometry defined by C and N atoms of the palladacycle as well as by two Se atoms of the chelating [Se2PPh2] ligand. The DFT computations have been performed to explore an electronic structure of the new complex and to explain experimental FT-IR frequencies. Besides, decomposition of the prepared complex has been studied by TGA/DSC.

Synthesis and characterization of iron and cobalt complexes with an asymmetric N-alkyl,N′-aryl-β-diketiminate ligand

An asymmetric N-alkyl,N′-aryl-β-diketiminate ligand L (L=2-((S)-(-)-1-phenylethylimino)-4-(2,6-diisopropylphenylimido)pentane) was prepared. Synthesis of solvent-free chloro-bridged dimers, [LFe(μ-Cl)]2 and [LCo(μ-Cl)]2 are presented. Upon reduction in the presence of cis-cyclooctadiene, rare examples of low-valent complexes LFe(cod) and LCo(cod) were obtained. All metal complexes were fully characterized by 1H NMR spectroscopy, elemental analysis, and X-ray crystallography. Crystallographic and spectroscopic results indicate that the N-alkyl,N′-aryl-β-diketiminate ligand L is sterically smaller but a better electron donor than the N,N′-diaryl-substituted β-diketiminate ligand LMe,Dipp (LMe,Dipp=2,4-bis(2,6-diisopropylphenylimido)pentane).

Iminopyridine-Based Cobalt(II) and Nickel(II) Complexes: Synthesis, Characterization, and Their Catalytic Behaviors for 1,3-Butadiene Polymerization.

A series of iminopyridine ligated Co(II) (1a–7a) and Ni(II) (1b–7b) complexes were synthesized. The structures of complexes 3a, 4a, 5a, 7a, 5b, and 6b were determined by X-ray crystallographic analyses. Complex 3a formed a chloro-bridged dimer, whereas 4a, 5a, and 7a, having a substituent (4a, 5a: CH3; 7a: Br) at the 6-position of pyridine, producing the solid structures with a single ligand coordinated to the central metal. The nickel atom in complex 5b features distorted trigonal-bipyramidal geometry with one THF molecule ligating to the metal center. All the complexes activated by ethylaluminum sesquichloride (EASC) were evaluated in 1,3-butadiene polymerization. The catalytic activity and selectivity were significantly influenced by the ligand structure and central metal. Comparing with the nickel complexes, the cobalt complexes exhibited higher catalytic activity and cis-1,4-selectivity. For both the cobalt and nickel complexes, the aldimine-based complexes showed higher catalyst activity than their ketimine counterparts.

Heteroleptic Complexes of Cyclometalated Platinum with Triarylformazanate Ligands.

Formazanates are a ligand class featuring a 1,2,4,5-tetraazapentadienyl core, with variable substitution at the 1, 3, and 5 positions. Here we describe a set of four heteroleptic cylcometalated platinum complexes containing triarylformazanate ligands. The complexes are prepared by metathesis reactions of chloro-bridged dimers [Pt(C∧N)(μ-Cl)]2 (C∧N = 2-phenylpyridine or 2-(2,4-difluorophenyl)pyridine) with triarylformazans in the presence of base. X-ray diffraction studies reveal the molecular structures of three such complexes. Cyclic voltammograms and UV-vis absorption spectra of the complexes show features characteristic of both the cyclometalated platinum fragment and the formazanate, with the latter giving rise to two reversible one-electron reductions in the CV and an intense visible π → π* absorption which is red-shifted by >100 nm relative to the free formazan. The electronic structures and redox properties of the complexes were further investigated by UV-vis spectroelectrochemistry and density functional theory calculations. All of the experimental and theoretical work points to a frontier molecular orbital manifold where the formazanate π and π* orbitals are substantially mixed with d-orbitals derived from the platinum center.

Manipulating the Excited States of Cyclometalated Iridium Complexes with β-Ketoiminate and β-Diketiminate Ligands.

A series of cyclometalated iridium complexes with β-ketoiminate and β-diketiminate ligands are described. Two different cyclometalating (C^N) ligands-2-phenylpridine (ppy) and 2-phenylbenzothiazole (bt)-are used in concert with three different ancillary (LX) ligands-a phenyl-substituted β-ketoiminate (acNac(Me)), a phenyl-substituted β-diketiminate (NacNac(Me)), and a fluorinated version of the β-diketiminate (NacNac(CF3))-to furnish a suite of six complexes. The complexes are prepared by metathesis reactions of chloro-bridged dimers [Ir(C^N)2(μ-Cl)]2 with potassium or lithium salts of the ancillary LX ligand. Four of the complexes are characterized by X-ray crystallography, and all six were subjected to in-depth optical and electrochemical interrogation. Cyclic voltammetry shows both reduction and oxidation waves, with the latter strongly dependent on the identity of the LX ligand. The complexes are all luminescent, with the nature of the emissive excited state and the quantum yield (Φ) dependent on the identity of both the C^N and LX ligands. Whereas the complexes Ir(ppy)2(NacNac(Me)) and Ir(ppy)2(acNac(Me)) are weakly luminescent (Φ ≈ 0.01), the complexes Ir(bt)2(NacNac(Me)) and Ir(bt)2(acNac(Me)) are strongly luminescent, with the latter's quantum efficiency (Φ = 0.82) among the highest ever observed for cyclometalated iridium complexes. Fluorination of the NacNac ligand gives rise to completely disparate emission behavior suggestive of a NacNac-centered emissive state. The results described here, in comparison with previous groups' studies on acetylacetonate (acac) analogues, suggest that the weaker-field NacNac and acNac ligands raise the energy of the metal-centered HOMO, with energy of the HOMO increasing in the order NacNac(CF3) < acNac(Me) < NacNac(Me).

Iridium(III) Luminescent Probe for Detection of the Malarial Protein Biomarker Histidine Rich Protein-II

This work outlines the synthesis of a non-emissive, cyclometalated Ir(III) complex, Ir(ppy)2(H2O)2+ (Ir1), which elicits a rapid, long-lived phosphorescent signal when coordinated to a histidine-containing protein immobilized on the surface of a magnetic particle. Synthesis of Ir1, in high yields,is complete O/N and involves splitting of the parent cyclometalated Ir(III) chloro-bridged dimer into two equivalents of the solvated complex. To confirm specificity, several amino acids were probed for coordination activity when added to the synthesized probe, and only histidine elicited a signal response. Using BNT-II, a branched peptide mimic of the malarial biomarker Histidine Rich Protein II (pfHRP-II), the iridium probe was validated as a tool for HRP-II detection. Quenching effects were noted in the BNT-II/Ir1 titration when compared to L-Histidine/Ir1, but these were attributed to steric hindrance and triplet state quenching. Biolayer interferometry was used to determine real-time kinetics of interaction of Ir1 with BNT-II. Once the system was optimized, the limit of detection of rcHRP-II using the probe was found to be 12.8 nM in solution. When this protein was immobilized on the surface of a 50 µm magnetic agarose particle, the limit of detection was 14.5 nM. The robust signal response of this inorganic probe, as well as its flexibility of use in solution or immobilized on a surface, can lend itself toward a variety of applications, from diagnostic use to imaging.