含三芳胺基的吡啶甲酸衍生物及其环金属铱配合物的合成与性能

通过Ullmann反应和Negishi偶联反应, 合成了一种含三芳胺功能基的吡啶-2-甲酸衍生物; 并以此为辅助配体、1-苯基异喹啉为环金属配体, 设计合成了一种新型环金属铱配合物. 该配合物的二氯甲烷溶液, 在391～461 nm范围呈现了强烈的金属-配体电荷转移(MLCT)电子跃迁吸收带; 其最大发光波长为609 nm. 与传统的二(1-苯基异喹啉)(吡啶-2-甲酸)合铱配合物相比, 设计的环金属铱配合物具有增强的MLCT电子跃迁吸收和低的氧化电位, 是一种有发展潜力的红色磷光材料.     

A comparative study of the bonding in different halides of iridium

X-ray photoelectron spectroscopy and multiple scattering Xα calculations have been applied to a series of iridium halide complexes in order to corroborate the nature of the bondings inherent in this class of compounds. Our results seem to substantiate contentiously that higher oxidation states of iridium favor the formation of covalent bonds. This conclusion is based on the observation that (1) successive bombardment of the iridium species by Ar ions almost definitely leads to a configuration in which iridium is bound to at most one halide ion, and (2) the theoretical charge per ligand ion approaches systematically a value of {1?} in the limit as the formal oxidation state of iridium approaches {1+}. The theoretical results are further arthenticated by the fact that the experimental ionization energy of the Ir(4f) level in the different iridium halide complexes studied is seen to decrease as a result of exposure to Ar ions.     

Me2-NHC based robust Ir catalyst for efficient water oxidation

Me(2)-NHC proved to be a valuable ligand in iridium catalyzed water oxidation reactions, both when carried out electrochemically as well as upon oxidation with cerium ammonium nitrate. Mechanistic data suggest that water oxidation occurs efficiently at a well defined iridium species via a mononuclear pathway.     

Enantioselective iridium-catalyzed carbonyl allylation from the alcohol or aldehyde oxidation level using allyl acetate as an allyl metal surrogate

Protocols for highly enantioselective carbonyl allylation from the alcohol or aldehyde oxidation level are described based upon transfer hydrogenative C-C coupling. Exposure of allyl acetate to benzylic alcohols 1a-i in the presence of an iridium catalyst derived from [IrCl(cod)]2 and (R)-BINAP delivers products of C-allylation 2a-i. Employing isopropanol as terminal reductant, exposure of allyl acetate to aryl aldehydes 3a-i in the presence of an iridium catalyst derived from [IrCl(cod)]2 and (-)-TMBTP delivers identical products of C-allylation 2a-i. In all cases examined, exception levels of enantioselectivity are observed. Thus, enantioselective carbonyl allylation is achieved from the alcohol or aldehyde oxidation level in the absence of any preformed allylmetal reagents. These studies define a departure from preformed organometallic reagents in carbonyl additions that transcend the boundaries of oxidation level.     

One‐Pot Preparation of Imines from Nitroarenes by a Tandem Process with an Ir–Pd Heterodimetallic Catalyst

A new tandem catalytic process has been studied for a heterodimetallic complex containing both iridium and palladium fragments connected by a 1,2,4‐trimethyltriazolyldiylidene ligand. The process implies the unprecedented preparation of imines from the direct reaction of nitroarenes and primary alcohols. The global process comprises the following steps: 1) reduction of the nitroarene to an amine, 2) oxidation of the alcohol to aldehyde, and 3) condensation of the aldehyde and the amine to form the corresponding imine. The oxidation of the alcohol to aldehyde is promoted by the iridium fragment, while the reduction of the nitro group to amine is facilitated by palladium. A wide set of different catalytic systems has been studied, showing that the Ir/Pd complex 1 is a highly active and stable catalyst in the preparation of imines.     

Transformation of a Cp*–Iridium(III) Precatalyst for Water Oxidation when Exposed to Oxidative Stress

The reaction of [Cp*Ir(bzpy)NO₃] ( 1 ; bzpy=2‐benzoylpyridine, Cp*=pentamethylcyclopentadienyl anion), a competent water‐oxidation catalyst, with several oxidants (H₂O₂, NaIO₄, cerium ammonium nitrate (CAN)) was studied to intercept and characterize possible intermediates of the oxidative transformation. NMR spectroscopy and ESI‐MS techniques provided evidence for the formation of many species that all had the intact Ir–bzpy moiety and a gradually more oxidized Cp* ligand. Initially, an oxygen atom is trapped in between two carbon atoms of Cp* and iridium, which gives an oxygen–Ir coordinated epoxide, whereas the remaining three carbon atoms of Cp* are involved in a η³ interaction with iridium ( 2 a ). Formal addition of H₂O to 2 a or H₂O₂ to 1 leads to 2 b , in which a double MeCOH functionalization of Cp* is present with one MeCOH engaged in an interaction with iridium. The structure of 2 b was unambiguously determined in the solid state and in solution by X‐ray single‐crystal diffractometry and advanced NMR spectroscopic techniques, respectively. Further oxidation led to the opening of Cp* and transformation of the diol into a diketone with one carbonyl coordinated at the metal ( 2 c ). A η³ interaction between the three non‐oxygenated carbons of “ex‐Cp*” and iridium is also present in both 2 b and 2 c . Isolated 2 b and mixtures of 2 a – c species were tested in water‐oxidation catalysis by using CAN as sacrificial oxidant. They showed substantially the same activity than 1 (turnover frequency values ranged from 9 to 14 min^?1).     

Synthesis and coordination chemistry of organoiridium complexes supported by an anionic tridentate ligand

Treatment of deprotonated N-(dimethylaminoethyl)-2-diphenylphosphinoaniline with bis(cyclooctene)iridium chloride dimer affords a thermally stable iridium(I) olefin complex. Infrared analysis of the corresponding monocarbonyl iridium(I) compound indicates a relatively electron rich metal center. Reaction of the iridium(I) cyclooctene complex with iodomethane effects oxidation of the metal yielding a five-coordinate iridium(III) methyl iodide complex which reversibly coordinates tetrahydrofuran. X-ray crystallography confirms coordination of ether to the iridium(III) methyl iodide complex and NMR spectroscopic experiments establish an equilibrium constant of 1.66(9) M for tetrahydrofuran binding. A five-coordinate iridium(III) dimethyl complex has also been prepared and characterized by X-ray diffraction. Hydrogenolysis of the dialkyl species permits identification of a short-lived classical iridium(III) dihydride complex.     

Enantioselective iridium-catalyzed carbonyl allylation from the alcohol or aldehyde oxidation level via transfer hydrogenative coupling of allyl acetate: departure from chirally modified allyl metal reagents in carbonyl addition

Under the conditions of transfer hydrogenation employing an iridium catalyst generated in situ from [Ir(cod)Cl]2, chiral phosphine ligand (R)-BINAP or (R)-Cl,MeO-BIPHEP, and m-nitrobenzoic acid, allyl acetate couples to allylic alcohols 1a-c, aliphatic alcohols 1d-l, and benzylic alcohols 1m-u to furnish products of carbonyl allylation 3a-u with exceptional levels of asymmetric induction. The very same set of optically enriched carbonyl allylation products 3a-u are accessible from enals 2a-c, aliphatic aldehydes 2d-l, and aryl aldehydes 2m-u, using iridium catalysts ligated by (-)-TMBTP or (R)-Cl,MeO-BIPHEP under identical conditions, but employing isopropanol as a hydrogen donor. A catalytically active cyclometallated complex V, which arises upon ortho-C-H insertion of iridium onto m-nitrobenzoic acid, was characterized by single-crystal X-ray diffraction. The results of isotopic labeling are consistent with intervention of symmetric iridium pi-allyl intermediates or rapid interconversion of sigma-allyl haptomers through the agency of a symmetric pi-allyl. Competition experiments demonstrate rapid and reversible hydrogenation-dehydrogenation of the carbonyl partner in advance of C-C coupling. However, the coupling products, which are homoallylic alcohols, experience very little erosion of optical purity by way of redox equilibration under the coupling conditions, although isopropanol, a secondary alcohol, may serve as terminal reductant. A plausible catalytic mechanism accounting for these observations is proposed, along with a stereochemical model that accounts for the observed sense of absolute stereoinduction. This protocol for asymmetric carbonyl allylation transcends the barriers imposed by oxidation level and the use of preformed allyl metal reagents.     

Disposable amperometric sensor for neurotransmitters based on screen-printed electrodes modified with a thin iridium oxide film.

Potential cycling in the range from -0.2 to +1.2 V is used for the electrodeposition of hydrous iridium oxide films onto a screen-printed electrode from a saturated solution of alkaline iridium(III) solution. The iridium oxide redox couple shows a stable and obvious reversible redox, with the formal potential being pH dependent in the range 1-14. The properties, stability and electrochemical properties of iridium oxide films were investigated by cyclic voltammetry. A modified electrode showed excellent catalytic activity toward the oxidation of neurotransmitters (catecholamines) over a wide pH range (2-8). The electrocatalytic behavior is further exploited as a sensitive detection scheme for adrenaline and dopamine by hydrodynamic amperometry. Under the optimized conditions, the calibration curves are linear in the concentration range 0.1-70 and 0.1-15 microM for dopamine and adrenaline determination, respectively. The detection limit and sensitivity are 30 nM and 30 nA/microM for adrenaline and 15 nM and 80 nA/microM for dopamine. Finally, the analytical performance of the modified electrode was demonstrated for the elimination of interference by uric acid in catecholamines determination when present in a 1000-fold concentration excess.     

Mechanism of iridium(III) catalysis in the oxidation of diols by N-bromoacetamide

Summary The kinetics of iridium(III)-catalysed oxidation of 1,2-ethanediol and 1,4-butanediol by N-bromoacetamide (NBA) in HClO₄ in the presence of [Hg(OAc)₂] as a scavenger for Br^– have been investigated. The reactions are zero-order with respect to both diols, and first-order in NBA at low NBA concentrations, tending to zero order at high concentrations. The order in Ir^III decreases from unity to zero at high iridium(III) concentrations. A positive effect on the oxidation rate is observed for [H⁺] and [Hg^II] whereas a negative effect is observed for acetamide and [Cl^–]. Ionic strength does not influence the oxidation rate. (H₂OBr)⁺ is postulated as the oxidizing species. A mechanism consistent with the observed kinetic data is proposed.     

Comparison of amorphous iridium water-oxidation electrocatalysts prepared from soluble precursors

Electrodeposition of iridium oxide layers from soluble precursors provides a route to active thin-layer electrocatalysts for use on water-oxidizing anodes. Certain organometallic half-sandwich aqua complexes of iridium form stable and highly active oxide films upon electrochemical oxidation in aqueous solution. The catalyst films appear as blue layers on the anode when sufficiently thick, and most closely resemble hydrous iridium(III,IV) oxide by voltammetry. The deposition rate and cyclic voltammetric response of the electrodeposited material depend on whether the precursor complex contains a pentamethylcyclopentadieneyl (Cp*) or cyclopentadienyl ligand (Cp), and do not match, in either case, iridium oxide anodes prepared from non-organometallic precursors. Here, we survey our organometallic precursors, iridium hydroxide, and pre-formed iridium oxide nanoparticles. From electrochemical quartz crystal nanobalance (EQCN) studies, we find differences in the rate of electrodeposition of catalyst layers from the two half-sandwich precursors; however, the resulting layers operate as water-oxidizing anodes with indistinguishable overpotentials and H/D isotope effects. Furthermore, using the mass data collected by EQCN and not otherwise available, we show that the electrodeposited materials are excellent catalysts for the water-oxidation reaction, showing maximum turnover frequencies greater than 0.5 mol O(2) (mol iridium)(-1) s(-1) and quantitative conversion of current to product dioxygen. Importantly, these anodes maintain their high activity and robustness at very low iridium loadings. Our organometallic precursors contrast with pre-formed iridium oxide nanoparticles, which form an unstable electrodeposited material that is not stably adherent to the anode surface at even moderately oxidizing potentials.     

A theoretical study of the mechanism for the homogeneous catalytic reversible dehydrogenation-hydrogenation of nitrogen heterocycles

A mechanism for the dehydrogenation reaction of 1,2,3,4-tetrahydroquinoline to quinoline derivatives, catalyzed by a Cp*Ir complex containing a 2-pyridonate ligand, is proposed and supported by theoretical calculations at the B3LYP level. The proposed mechanism involves two stages which are all thermodynamically unfavorable (endothermic by 36.3 kcal mol(-1) and 18.4 kcal mol(-1), respectively). The apparent activation energies of the first and second stages of the reaction are 30.8 kcal mol(-1) and 34.0 kcal mol(-1), respectively, and are considered overestimates of the entropy change of reaction. Owing to a decrease in the oxidative ability of iridium(III) coordinated to large electronegative nitrogen and chlorine, ligand promoted hydrogen abstraction is crucial at both stages of dehydrogenation, in which the oxidation state of iridium(III) does not change, and the ligand 2-pyridonate is converted to 2-hydroxypyridine. Cp*Ir(C(5)NH(4)OH)ClH, an important intermediate, releases hydrogen through an energy barrier of 23.5 kcal mol(-1).     

钯、铱单取代十二钼磷酸盐的制备及性质的研究

本文报道了Pd 、Ir 　取代的十二钼磷酸四丁基铵盐 (α (n Bu4 N) 5[PMo11Pd(OH2 )O39]、α (n Bu4 N) 3[PMo11Ir(OH2 )O39])的制备方法。IR、UV及31P NMR证实产物仍保持Keggin结构 ,并有一个Mo 为Pd 、Ir 所取代。电化学上 ,Ir 取代化合物存在三个清晰的多酸骨架氧化 还原峰而Pd 取代化合物由于电极吸附作用使它的氧化 还原峰无法被观察到。在两个取代化合物的烯烃催化氧化中醇、酮为主要产物。　值得注意的是 ,Pd 取代化合物催化的反应中苯酚取代环己烯酮而成为主要产物     

Donor‐Flexible Nitrogen Ligands for Efficient Iridium‐Catalyzed Water Oxidation Catalysis

A pyridylideneamide ligand with variable donor properties owing to a pronounced zwitterionic and a neutral diene‐type resonance structure was used as a dynamic ligand at a Cp* iridium center to facilitate water oxidation catalysis, a reaction that requires the stabilization of a variety of different iridium oxidation states and that is key for developing an efficient solar fuel device. The ligand imparts high activity (nearly three‐fold increase of turnover frequency compared to benchmark systems), and exceptionally high turnover numbers, which indicate a robust catalytic cycle and little catalyst degradation.     

Preparing of Iridium Oxide Film Modified Microelectrode as an Amperometric Detector in FIA for Determination of Epinephrine

Abstract

Iridium oxide film modified microelectrode with a tip diameter of 25 µm was constructed using anodically grown iridium oxide film. The iridium oxide film, which was formed at the tip of the iridium wire by cyclic voltammetry in dilute sulfuric acid, showed excellent catalytic activity towards the oxidation of epinephrine. The stability and electrochemical properties of iridium oxide film modified microelectrode along with catalytic oxidation of epinephrine was studied. An oxidation peak was observed at 0.28 V. The electron‐transfer number (n) was 2. The iridium oxide film modified microelectrode was used as a detector in flow injection system for determination of epinephrine. Under the optimized conditions, the calibration curve was linear in the concentration range of 1.0×10^?8 to 1.0×10^?5 mol/l for epinephrine, with a detection limit of 1.0×10^?9 mol/l. The iridium oxide film modified microelectrode was used for direct determination of the epinephrine in human serum samples. The flow injection analysis was precise detection method of epinephrine and time saving device.     

Consecutive iridium catalyzed C-C and C-H bond forming hydrogenations for the diastereo- and enantioselective synthesis of syn-3-fluoro-1-alcohols: C-H (2-fluoro)allylation of primary alcohols

Commercially available (2-fluoro)allyl chloride serves as an efficient allyl donor in highly enantioselective iridium catalyzed carbonyl (2-fluoro)allylations from the alcohol or aldehyde oxidation level via transfer hydrogenation. Diastereoselective Crabtree hydrogenation of the resulting homoallylic alcohols provides syn-3-fluoro-1-alcohols.     

Oxygen-atom transfer from carbon dioxide to a Fischer carbene at (PNP)Ir

Dehydrogenation of the dihydride (PNP)IrH2 with norbornylene in the presence of t-butyl methyl ether leads to formation of an iridium(I) Fischer carbene complex, (PNP)Ir C(H)OtBu, by double C-H activation and loss of H2. The square planar pincer-type carbene effects quantitative oxygen-atom transfer from CO2 (1 atm) at ambient temperature to generate t-butyl formate and (PNP)Ir-CO. The iridium carbene reacts similarly with carbonyl sulfide and phenyl isocyanate, causing sulfur-atom and nitrene-group transfer, respectively. In the absence of a hydrogen acceptor, thermolysis of (PNP)IrH2 in t-butyl methyl ether under an atmosphere of CO2 also results in the formation of (PNP)Ir-CO and oxidation of t-butyl methyl ether to t-butyl formate via an iridium carbene. Preliminary mechanistic studies indicate that these reactions proceed through an intermediate four-membered metallalactone.     

Synthesis, Molecular Structure, and Vibrational Spectra of mer-Tris(carbonyl)iridium(III) Fluorosulfate, mer-Ir(CO)(3)(SO(3)F)(3)

Addition of carbon monoxide (0.5-2 atm) to iridium(III) fluorosulfate, Ir(SO(3)F)(3), dissolved in HSO(3)F over 4 days and at 60 degrees C, results in the quantitative formation of tris(carbonyl)iridium(III) fluorosulfate Ir(CO)(3)(SO(3)F)(3). Slow evaporation of the solvent produces single crystals of mer-Ir(CO)(3)(SO(3)F)(3). Crystal structure data for mer-Ir(CO)(3)(SO(3)F)(3): monoclinic, space group P2(1)/c, Z = 4, a = 8.476(1) ?, b = 12.868(2) ?, c = 12.588 (1) ?, beta = 108.24(1) degrees, V = 1304.0 ?(3), T = 200 K, R(F)() = 0.022 for 2090 data (I(o) >/= 2.5sigma(I(o))) and 200 variables. Vibrational spectra of the crystalline solid are consistent with a mer-isomer with CO stretching modes at 2249 (A(1)), 2208 (B(1)), and 2198 (A(1)) cm(-)(1) in the IR spectrum. In solution of HSO(3)F, additional CO stretching bands attributed to the fac-isomer are found in the FT-Raman and IR spectra at 2233 (A(1)) and 2157 cm(-)(1) (E). Additional evidence for a mixture of fac- and mer-isomers comes from (19)F NMR spectra. The vibrational spectra suggest strongly reduced iridium to CO pi-back-bonding. The crystal structure reveals significant intra- and intermolecular contacts between the electropositive C atom of the CO groups and O or F atoms of the fluorosulfate groups. Hence mer-tris(carbonyl)iridium(III) fluorosulfate becomes the first thermally stable, structurally characterized, and predominantly sigma-bonded carbonyl derivative of a metal in the +3 oxidation state.     

Iridium-catalyzed hydrogenation of N-heterocyclic compounds under mild conditions by an outer-sphere pathway

A new homogeneous iridium catalyst gives hydrogenation of quinolines under unprecedentedly mild conditions-as low as 1 atm of H(2) and 25 °C. We report air- and moisture-stable iridium(I) NHC catalyst precursors that are active for reduction of a wide variety of quinolines having functionalities at the 2-, 6-, and 8- positions. A combined experimental and theoretical study has elucidated the mechanism of this reaction. DFT studies on a model Ir complex show that a conventional inner-sphere mechanism is disfavored relative to an unusual stepwise outer-sphere mechanism involving sequential proton and hydride transfer. All intermediates in this proposed mechanism have been isolated or spectroscopically characterized, including two new iridium(III) hydrides and a notable cationic iridium(III) dihydrogen dihydride complex. DFT calculations on full systems establish the coordination geometry of these iridium hydrides, while stoichiometric and catalytic experiments with the isolated complexes provide evidence for the mechanistic proposal. The proposed mechanism explains why the catalytic reaction is slower for unhindered substrates and why small changes in the ligand set drastically alter catalyst activity.     

Size and pressure independent kinetics of CO oxidation on alumina‐supported iridium nanoparticles

The gas‐phase oxidation of CO catalyzed by iridium was studied under CO‐rich reactant conditions over the pressure range 10^?4–10^?2 Pa to investigate the controversial size and pressure dependencies. The reactivity of iridium clusters with an average size of 3 nm was compared to macroscopic metal particles with extended single crystal facets over a range of temperatures (433–573 K), and the apparent activation energies for CO oxidation were consistent with the known activation energies for CO desorption from iridium surfaces. No size‐specific dependence of the reaction kinetics was measured, and no indication of the previously reported “pressure gap” was observed. Unlike many other transition metal catalysts, iridium may be used as a model catalyst for CO oxidation in different morphological forms over a range of pressures without invoking a change in the kinetic model. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 826–830, 2008