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Abstract: The mechanism of the iridium-catalyzed functionalization of a primary C-H bond at the γ position of an alcohol (5) is investigated by density functional theory (DFT) calculations. A new [...]

Mixed-valence ruthenium (Ru[O.sub.x]) and iridium (Ir[O.sub.x]) oxides and composites on their basis (Ru[O.sub.x]-Ir[O.sub.x] or Ir[O.sub.x]-Ru[O.sub.x]) electrodeposited onto the surface of a glassy carbon electrode exhibit a catalytic activity in the electrooxidation of uric acid, xanthine, and hypoxanthine. The transition from metal oxides to composites of two mixed-valence metal oxides leads to an increase in the catalytic effect of the oxidation of hydroxypurines. The Ir[O.sub.x]-Ru[O.sub.x] composite demonstrated the highest catalytic activity. Procedures for the amperometric detection of hydroxypurines on this composite electrode under the conditions of flow-injection analysis (FIA) and sequential injection analysis are proposed. A linear dependence of an analytical signal on the analyte concentration is observed in the range 1 x [10.sup.-6] to 5 x [10.sup.-3] M for uric acid and xanthine and 5 x [10.sup.-7] to 5 x [10.sup.-3] M for hypoxanthine under FIA conditions and from 5 x [10.sup.-7] to 5 x [10.sup.-3] M for uric acid and xanthine and 5 x [10.sup.-8] to 5 x [10.sup.-3] M for hypoxanthine in sequential injection analysis. Under FIA conditions, the sensitivity, rapidity, and performance of the analysis increase compared to the stationary conditions. The advantages of sequential injection analysis over FIA include a lower consumption of the supporting electrolyte; the absence of pumps and connections; and an increase in sensitivity, reproducibility, and rapidity. Keywords: chemically modified electrodes, mixed-valence ruthenium and iridium oxides, electrooxidation of hydroxypurines, flow injection analysis, sequential injection analysis DOI: 10.1134/S106193481409010X, Hydroxypurines--hypoxanthine (HX), xanthine (X), and uric acid (UA)--are products of the metabolism of purine bases. The control of the concentration of these substances in biological fluids facilitates the diagnostics of [...]

Density functional theory (DFT) is used to explore the competitive C--H and C--Cl oxidative additions (OA) of chlorobenzene to the cationic Ir(I) complex: [[(PNP*)[Ir.sup.I]].sup.+] [PNP* = 2,6- bis((dimethylphosphino)methyl)pyridine]. Consistent with [...]

The synthesis and characterization of neutral heteroleptic molecular iridium(III) complexes with (2,4-difluoro)phenylpyridine and different pyridine-1,2,4-triazole ligands are described. The studies have shown high external quantum efficiencies and color points better than the standard for blue iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,[C.sup.2]]picolinate.

The synthesis and photophysics properties of new homocysteine-selective sensor based on the iridium(III) complex are described. The studies have shown that the complex can selectively recognize homocysteine over other amino acids and thiol-related peptides through a color change.

The studies about the photophysical and electrochemical properties of [Ir[(ppy or pq).sub.2] (substituted-1,10-phenanthroline)]-[P[F.sub.6]] (ppy = 2-phenypyridine, pq = 2-phenylquinoline) is presented. The results provide insight into nature and number of the phenanthroline substituents to tune the color, quantum yield, and lifetime of the emission.

Cyclometalated iridium(III) coumarin complexes represent new types of probes for optical oxygen sensing. In comparison to the most commonly used ruthenium(II) polypyridyl dyes and porphyrin complexes with platinum group metals, they possess much more efficient visible absorption and higher quantum yields, which results in much higher brightnesses. Spectral properties and oxygen sensitivity can be fine-tuned by varying the nature of the coumarin ligand and using respective monomeric or dimeric complexes. When incorporated in a model polystyrene film the probes show optimal dynamics of luminescence decay time for oxygen monitoring in the range from 0% to 100% air saturation. Cross-sensitivity to temperature is significantly lower than for the commonly used ruthenium(II)-tris-4,7-diphenyl-1,10-phenanthroline oxygen probe. The probes, however, exhibit significantly lower photostability, which restricts their application. If long-term measurements are not required, the probes can be successfully used for reliable monitoring of oxygen concentration. High brightness of the complexes makes them particularly attractive for application in thin films (for monitoring of fast processes) and various types of nano- and microparticles, including magnetic beads. If temperature compensation is not applied, the novel optodes result in the lower errors in determination of oxygen content.

A series of new blue-phosphorescent iridium(III) complexes with ligands of 2-phenylimidazo[1,2-alpyridine (pip) derivatives were prepared to investigate their electrochemical, photophysical, and electroluminescent (EL) properties. Results found that combination of electron-withdrawing substituents on the phenyl ring with the use of another ancillary ligand enabled further blue shifts.

Studies were conducted to explore the electronic properties of the cyclometalated (C^N) complexes of iridium and platinum metals with catechol ligand. The complexes were observed to exhibit a reversible reduction of the semiquinone form to the catechol form of the ligand and an irreversible oxidation to the unstable quinone form of the ligand.

The synthesis, structure, photophysical and electrochemical properties of cyclometalated iridium complexes with ancillary cyano and isocyanide ligands are reported. The lack of solvatochromism and highly structured emission has indicated that the lowest energy excited state is triplet ligand centered with some admixture of singlet metal-to-ligand charge-transfer character.

The mechanism for triplet energy transfer from the green-emitting fac-tris[2-(4'-tert-butylphenyl)pyridinato]-iridium (Ir[(tBu-ppy).sub.3]) complex to the red-emitting bis[2-(2'-benzothienyl)pyridinato-N,[C.sup.3')(acetylacetonato)-iridium (Ir[(btp).sub.2](acac)) phosphor is reported. The findings suggest that the triplet energy transfer occurs via the Forster mechanism when the transition dipole moments involved on energy donor and acceptor are not neglible.

Reversible coordination networks are developed by compounding diphenylphosphinite telechelic polytetrahydrofuran with [[RhCl(COD)].sub.2] or [[IrCl(COD)].sub.2] in chloroform. Findings reveal that both systems result in stable gels at concentrations above 50 and 30 g/L for the rhodium(I) and iridium(I) networks.

Three dinuclear iridium(III) complexes consisting of a conjugated bis-tpy type bridging ligand and cyclometallating capping tridentate ligands of the 1,3-di-2-pyridylbenzene family are prepared (tpy = 2,2',6',2''-terpyridine). The results have shown that the smallest dinuclear species exhibits excited-state properties, with a weak but noticeable luminescence at room temperature that is not found in the mononuclear precursor.

The NMR, UV-visible absorption, and emission spectroscopy and electrochemical methods were used to synthesize and characterize a highly luminescent novel cationic iridium complex [iridium bis(2-phenylpyridine)(4,4'-(dimethylamino)-2,2'-bipyridine)]P[F.sub.6]. Single-layer light-emitting electrochemical cells with the charged complex as conducting and electroluminescent material sandwiched between indium-tin oxide and Ag electrodes were fabricated, which emit green-blue light with an onset voltage as low as 2.5 V.

A dual microelectrode electrochemical time-of-flight technique in which diffusion flux of [Ag.sup.+], [Cl.sup.-], or [H.sup.+] ions electrochemically produced at a generator electrode is measured by recording potential--time transients with Ag, Ag/AgCl, or iridium oxide potentiometric microsensors, respectively, is developed. The generator and microsensor electrodes are typically spaced by 50-100 [micro]m and are incorporated in the lithographically fabricated thin-layer-type devices. Under conditions of moderate rates of the ion electrogeneration, the potential--time (E--t) transients recorded with the three microsensors show excellent agreement with theory involving linear diffusion equations and the experimentally determined Nernstian slopes of the microsensors. However, when the generator current, or the initial concentration of the primary ion of interest is low, appreciable delays in the recorded E--t transients are observed due to the finite capacitance of the micro-potentiometric sensors. The recorded delay in the E--t transients can be quantitatively accounted for by including the sensor capacitance (C) in the theoretical description of the transients. Direct comparison between the theoretical and the experimental E--t transients yields the sensor's capacitance. This capability of our new technique is unique in that it allows determination of the capacitance of a potentiometric sensor at open circuit. In the cases of silver electrodes, this method results in C = 31 [+ or -] 2 [micro]F/ [cm.sup.2], a value that is in agreement with those obtained by other methods. The results for silver chloride sensors yield a C in the range of 100-140 [+ or -] 10 [micro]F/[cm.sup.2]. The specific values depend on sensor preparation and the resulting roughness of the Ag/AgCl interface. Iridium oxide sensors show a capacitance that linearly depends on the thickness of the film. Specific capacitance of these microporous films was determined to be 59 [+ or -] 6 F/[cm.sup.3].

Abstract -- The kinetics of noncatalytic and catalytic oxidation reactions of 4-amino-4'-methoxydiphenylamine with different oxidants in aqueous solutions and in the presence of surfactants was studied. The catalytic activity of [...]

The deuterium NMR spectra of the ternary metal deuterides (TMDs) [Ca.sub.2]Rh[D.sub.5] and [Ca.sub.2]Ir[D.sub.5] has shown that the disorder is dynamic at room temperature. The differential scanning calorimetric study of the transition in [Ca.sub.2]Ir[H.sub.5] has located a reversible phase transition at 284 K with an enthalpy change of 650 J [mol.sup.-1] and entropy change of 2.3 J [K.sup.-1] [mol.sup.-1].

The synthesis of the phosphine sulfide derivative of 1-[P.sub.i][Pr.sub.2-]indene, the use of this ligand in the preparation of neutral [[k.sup.2]-C,S] and cationic [[k.sup.2-H,S] Rh and Ir coordination complexes and the application of these complexes as catalysts for the addition of triethylsilane to styrene are reported. The observations reveal that species as well as monoanionic derivatives differ considerably in their coordination chemistry.

A novel amperometric biosensor for performing simultaneous electrochemical multianalyte immunoassays is described. The sensor consisted of eight iridium oxide sensing electrodes (0.78 [mm.sup.2] each), an iridium counter electrode, and a Ag/AgCl reference electrode patterned on a glass substrate. Four different capture antibodies were immobilized on the sensing electrodes via adsorption. Quantification of proteins was achieved using an ELISA in which the electrochemical oxidation of enzyme-generated hydroquinone was measured. The spatial separation of the electrodes enabled simultaneous electrochemical immunoassays for multiple proteins to be conducted in a single assay without amperometric cross-talk between the electrodes. The simultaneous detection of goat IgG, mouse IgG, human IgG, and chicken IgY was demonstrated. The detection limit was 3 ng/mL for all analytes. The sensor had excellent precision (1.9-8.2% interassay CV) and was comparable in performance to commercial single-analyte ELISAs. We anticipate that chip-based sensors, as described herein, will be suitable for the mass production of economical, miniaturized, multianalyte assay devices.

A series of complexes of the type Cp*IrCl2(NHC) were synthesized with the aim of evaluating the capabilities in C-H activation, specifically in H/D exchange of a wide range of organic molecules. The Cp*IrCl2(NHC) catalysts are tested in the deuteration of organic molecules, using CD3OD as deuterium source.

A study to examine the catalytic properties of small clusters of rhodium and of iridium on oxide supports using the hydrogenation reaction of ethene, propene, and toluene was conducted. The results indicated self-inhibition of reaction adsorbed hydrocarbons and differences between ethene hydrogenation and propene hydrogenation that may arise primarily from different adsorbate-adsorbate interactions.

Coordination of 4'-(C6H4-p-X)-2,2':6',2'-terpyridines[X = NO2, NBu2, (E)-CH=CH-C6H4-p-NBu2, (E,E)-(CH=CH)2-C6H4-p-NMe2] to Zn(II), Ru(III), and Ir(III) metal centers induces a significant enhancement of the absolute value of their second-order nonlinear optical (NLO) response. Varying the nature of the metal center, the second order NLO response shifts from positive to negative, being controlled by metal-to-ligand, ligand-to-metal or intraligand charge-transfer transitions.

A series of cationic bis-cyclometalated iridium(III) complexes are synthesized and their electrochemical, photophysical, electroluminescent properties are studied. The complexes are found to be luminescent both in a fluid solution and as neat solids at 298 K, while single-layer electroluminescent devices that give blue, green, and red electroluminescence are also fabricated.

The strong counterion effects in the reaction of 2-pyridylmethyl imidazolium salts with IrH5(PPh3)(sub 2) to give chelating NHC(super 13-18) complexes, where NHCs are bound to either at C2 or at C5 depending on the anion, are described. The results indicate that the relative energetics of the normal versus the abnormal forms is strongly affected by choice of anion and hence big anion effects are observed.

A series of heteroleptic Ir(III) metal complexes bearing two N-phenyl-substituted pyrazoles and one 2-pyridyl pyrazole ligands are synthesized and characterized to attain highly efficient, room temperature blue phosphorescence. The results on the basis of steady-state, relaxation dynamics, and theoretical approaches, lead to a conclusion that the weakening of iridium metal-ligand bonding strength in the T1 state plays a crucial role for the fast radiationless deactivation.

Abstract -- The formation of ion pairs of Rh(III) and Ir(III) with pyruvic acid acylhydrazones and symmetric cyanine dyes, derivatives of 1,3,3-trimethyl-3H-indolium, was studied. It was demonstrated that rhodium and [...]

The synthesis and structural peculiarities of iridium complexes exhibiting a novel eta(super 1)-N,eta(super 2)-C,C-binding interaction between the pyridinyl-functionalized fulvene ligand and the metal center are described. The efforts to prepare cyclometalated Ir and Pt complexes with ligands containing smaller pi systems than those of the phenyl-pyridines are still underway.

The design of homogeneous catalysts based on Ir and other late transition metal complexes using O-donor ligands like acetylacetonate (aca), tropolone, aryloxides, catechols, hydroxyaetophenone to stabilize the complexes to the reaction conditions needed for generating functionalized products is discussed. The outcome of the studies helps to utilize, design new, more effective, thermally protic-and oxidant-stable O-donor catalysts for hydrocarbon conversion.

The intrinsic gas-phase stability of the IrCl6(super 3 -) trianion and its microsolvated clusters, IrCl6(super 3 -).(H2O)(sub n) n = 0-10, is investigated. Calculations indicate that the bare trianion is metastable with respect to decay via both electron detachment and ionic fragmentation.

The synthesis and photophysical characterization of a series of (N,C(super 2')-(2-para-tolylpyridyl)2Ir(LL') [tpy)2Ir(LL')] (LL' = 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tert-butylisocyanide (CN-t-Bu) are reported. The electrochemical and photophysical properties of the (typ)2Ir(LL') complexes are discussed in detail.

An efficient methodology is developed for the reductive alkylation of secondary amine with aldehyde and Et(sub 3)SiH using an iridium complex as a catalyst. A variety of secondary amines could be alkylated by allowing them to react with aldehydes and polymethylhydrosiloxane in the presence of an iridium catalyst to afford the corresponding tertiary amines in excellent yields.

Two-electron mixed-valence di-iridium alkyl complexes react with hydrogen in a cascade reaction to produce a trihydride and alkane. The overall reaction sequence depends critically on hydrogen migration to and from a bridging position.

The synthesis of new ligand systems incorporating two and three 4,4'-bipyridine units are described. These complexes were fully characterized by X-ray structural analysis.

A mechanistic study of the stoichiometric and catalytic H/D exchange reactions involving cationic iridium complexes is presented. The catalytic H/D exchange reaction is not catalyzed by simple H(super +) transfer, but instead proceeds by a reversible C-H bond activation mechanism.

Reversible dihydrogen uptake by a two-electron mixed-valence di-iridium complex is examined with nonlocal density-functional calculations. The investigation establishes a ligand-design criterion for attaining cooperative bimetallic reactivity, namely, that the supporting ligand framework is mechanically flexible enough to accommodate the nuclear reorganizations that accompany substrate activation.

The assembly of Ir4(Co)12 from Ir(CO)2(acac) precursors in the supercages of the zeolite NaY is investigated by extended X-ray absorption fine structures (EXAFS) and in-situ infrared (IR) spectroscopies. The results revealed that conditions of pretreatment of the zeolite significantly affect the chemistry of the intercage cluster assembly of Ir4(Co)12 in zeolites nanopores.

The introduction of chiral centers in the ligands, in this case the pienne groups attached to the pyridine ring of phenylpyridine, leads to only modest stereo-selectivity with respect to helical configuration of the octahedral Ir(III)-center in a tris-didentate cyclometalated complex. Beside the stereo control, the introduction of the pinene groups into the ligand has the benefit of rendering these uncharged molecules highly soluble in a large range of solvents.

A series of luminescent cyclometalated Ir(III) complexes are synthesized and evaluated for use in unimolecular oxygen-sensing materials. The complexes Ir(C6)(sub 2)(vacac) and mer-Ir(ppy)(sub 2)(vppy) displayed the longest luminescence lifetimes and largest quantum efficiencies in solution making them ideal candidates for future oxygen-sensing studies.

The photoluminescence (PL) dynamics of Ir(ppy)(sub 3)-cored dendrimers with the simple molecule Ir(ppy)(sub 3) in solution, blends, and neat films are discussed. Extensive aggregation of Ir(ppy)(sub 3) molecules is indicated by their rough surface with aggregated region of rodlike structure, as obtained by atomic force microscopy, which suggests that the PL quenchers in neat Ir(ppy)(sub 3) films may be excimers.

The ionic interactions in aqueous solutions of Na3IrCl6 + Pb(NO3)2 are studied for developing a facilitated electrosynthesis of iridium-based catalytic surfaces. The results indicate that synergistic electroplating of ion pair charge-transfer could be applicable to other transition or posttransition metal redox systems.

A study on the molecular design of a highly efficient red-phosphorescent complex suitable for red OLED devices is conducted. With a decrease in the energy of the lowest excited triplet state, the Kr value of phosphorescence from the Ir(thp)(sub 3) family significantly decreases, thereby leading to a low quantum yield of red phosphorescence.

The isolation and structural determination of a water-soluble hydride complex that serves as a robust and highly active catalyst for acid-catalyzed transfer hydrogenations of carbonyl compounds at pH 2.0-3.0 at 70 degree C is reported. The rate of the acid-catalyzed transfer hydrogenation is drastically dependent on pH of the solution, reaction temperature, and concentration of HCOOH.

The potential of iridium complexes of the N-heterocyclic carbene oxazoline ligands in asymmetric hydrogenations of arylalkenes is examined. Pressure dependence studies disclosed that many reactions performed with high conversions and optimal enantioselectivities in approximately 2h when only 1 bar of hydrogen was used.

A theoretical study of the TpIrH (sub 4) system is discussed. A comparison of the experimental infrared spectrum of TpIrH4 and harmonic frequency calculations support the assignment of C (sub s) and C (sub i) structures.

It is found that incorporation of SnO2 and Sb2O5 into IrOx not only saved the precious content significantly but also generated a synergic effect to make Ti/IrOx-Sb2O5-SnO2 much more stable. Ternary IrOx-Sb2O5-SnO2 is a promising electocatalyst for O2 evolution.

The syntheses and study of the spectroscopic, redox, and photophysical properties of a new set of species based on Ir(III) cyclometalated building blocks are described. The results suggest that the photoinduced energy transfer across the ester-linked bridging ligands seems to occur with low efficiency for the dinuclear mixed-chromophore species.

The nanosized Rulr bimetallic clusters in the NaY zeolite show strong resistance for the agglomeration in 1-atm oxygen and at high temperatures, compared to the Ru/NaY. Nanosized Rulr bimatallic clusters containing of 30-60 atoms can be obtained from the thermal decomposition and reduction with hydrogen of the precursor zeolite containing Ru complex and Ir (NH3)5(H2O)3+ free of chloride.

A study of the paddlewheel complexes with Ir(sub 2)(super 5+) cores having an unpaired electron are prepared by reacting (COD)Ir(super 1)(DArF)(sub 2)Ir(super III)(CF3CO2)(sub 2)(H2O) with two molar equivalents of HDArF (DArF = N,N'-diarylformamidinate, Ar = p-anisyl and p-chlorophenyl, and COD = 1,5-cyclooctadiene). The results show that in the presence of CH2Cl2, the corresponding Ir(sub 2)(mu-DArF)(sub 4)(n(super 1)-O2CCF3).2CH2Cl2 compounds are isolated in ca. 50% yield.