Ir Cp Research Articles

Iridium Azocarboxamide Complexes: Variable Coordination Modes, C–H Activation, Transfer Hydrogenation Catalysis, and Mechanistic Insights

Azocarboxamides, a special class of azo ligands, display intriguing electronic properties due to their versatile binding modes and coordination flexibility. These properties may have significant implications for their use in homogeneous catalysis. In the present report, half-sandwich Ir–Cp* complexes of two different azocarboxamide ligands are presented. Different coordination motifs of the ligand were realized using base and chloride abstracting ligand to give N∧N-, N∧O-, and N∧C-chelated monomeric iridium complexes. For the azocarboxamide ligand having methoxy substituted at the phenyl ring, a mixture of N∧C-chelated mononuclear (Ir-5) and N∧N,N∧C-chelated dinuclear complexes (Ir-4) were obtained by activating the C–H bond of the aryl ring. No such C–H activation was observed for the ligand without the methoxy substituent. The molecular identity of the complexes was confirmed by spectroscopic analyses, while X-ray diffraction analyses further confirmed three-legged piano-stool structure of the complexes along with the above binding modes. All complexes were found to exhibit remarkable activity as precatalysts for the transfer hydrogenation of carbonyl groups in the presence of a base, even at low catalyst loading. Optimization of reaction conditions divulged superior catalytic activity of Ir-3 and Ir-4 complexes in transfer hydrogenation over the other catalysts. Investigation of the influence of binding modes on the catalytic activity along with wide range substrates, tolerance to functional groups, and mechanistic insights into the reaction pathway are also presented. These are the first examples of C–H activation in azocarboxamide ligands.

Rh(III) and Ir(III)Cp* Complexes Provide Complementary Regioselectivity Profiles in Intermolecular Allylic C–H Amidation Reactions

An efficient regioselective allylic C–H amidation of mono-, di-, and trisubstituted olefins has been developed. Specifically, the combination of dioxazolone reagents with RhCp* and IrCp* catalysts ...

Seasonal Distribution of Bemisia tabaci (Hemiptera: Aleyrodidae) MEAM1 Species and Impact on Incidence of Begomoviral Diseases in Baja California Sur.

For more than four decades, the presence of the whitefly Bemisia tabaci Gennadius complex as a pest and transmitter of begomoviral diseases has been one of the most important phytopathological events in cultivated species worldwide. In addition, the number of whitefly species, as well as the viruses they transmit, has been increasing over time. In the state of Baja California Sur (BCS), Mexico, the diversity of B. tabaci has been delimited to MEAM1 and NW species, affecting mainly tomato, pepper, and squash. However, the relationship of these species with the dispersion of the begomoviruses previously detected in the study area is still unknown. In a 5-yr study (2012-2016), these species of whiteflies and begomoviruses were identified. Moreover, the recurrence, seasonal distribution, and impact they have on the spread of the begomoviral diseases were assessed. The identification of whiteflies was done targeting the mtCOI by PCR-DNA barcoding assay. For begomoviruses identification, a set of degenerate and specific primers targeting the IR region and CP gene were used. To determine seasonal abundance, monitoring was performed every 15 d by means of yellow traps. The MEAM1 species in all localities was observed with the highest peak population (>10 whiteflies/trap) from March to April. The guidelines for naming begomovirus species for the International Committee on Taxonomy of Viruses (ICTV) establish that the names when they are preceded by the acronym the whole name is in lowercase, not italicized (e.g. bean golden mosaic virus (BGMV)); when the name goes alone without the acronym then its capitalizes the first letter (e.g. Bean golden mosaic virus) and when these are referred to in a taxonomic sense they are italicized and the first letter is capitalized (e.g. Bean golden mosaic virus). This study provides details of the distribution and occurrence of MEAM1 species and diversity of begomoviruses that could be useful in disease management in BCS and worldwide.

Simultaneous Functionalization of Carbon Surfaces with Rhodium and Iridium Organometallic Complexes: Hybrid Bimetallic Catalysts for Hydroamination

Carbon-based surfaces were explored here for the synthesis of heterometallic surface-bound catalysts. This takes advantage of catalytic enhancements found using bimetallic catalysts relative to monometallic analogues, as well as the advantages of heterogeneous catalysts over homogeneous catalysts. To achieve this, two organometallic cations with different metal centers, oxidation states, and coligands, [Rh(N,N′)(CO)2]+ and [Ir(N,N′)Cp*Cl]+ (N,N′ = pyrazolyltriazolylmethane ligands), were simultaneously immobilized onto the surface of carbon materials (carbon black and reduced graphene oxide). The relative concentration of the rhodium and iridium cations in the synthetic media was varied allowing for different metal ratios on the carbon surfaces. The composition of the complexes bound to the surfaces was confirmed using XPS which revealed the relative ratios of the iridium and the rhodium species on the surface, agreeing well with the values obtained by MP-AES. The materials were further characterized by N2 absorption. The qualitative distribution of rhodium and iridium ions on the carbon surfaces was determined by STEM-EDX, revealing a uniform distribution of both complexes on the carbon surfaces. The efficiency of the materials as catalysts for intramolecular hydroamination was investigated. The data acquired demonstrated that the optimized ratio of rhodium and iridium on the carbon black material led to more effective catalysts than their monometallic counterparts. Having both complexes on the same carbon black surface presented an improvement in the catalytic activity compared to the complexes immobilized on separate particles.

Ir-6: A Novel Iridium (III) Organometallic Derivative for Inhibition of Human Platelet Activation.

Platelet activation has been reported to play a major role in arterial thrombosis, cancer metastasis, and progression. Recently, we developed a novel Ir(III)-based compound, [Ir(Cp∗)1-(2-pyridyl)-3-(4-dimethylaminophenyl)imidazo[1,5-a]pyridine Cl]BF4 or Ir-6 and assessed its effectiveness as an antiplatelet drug. Ir-6 exhibited higher potency against human platelet aggregation stimulated by collagen. Ir-6 also inhibited ATP-release, intracellular Ca2+ mobilization, P-selectin expression, and the phosphorylation of phospholipase Cγ2 (PLCγ2), protein kinase C (PKC), v-Akt murine thymoma viral oncogene (Akt)/protein kinase B, and mitogen-activated protein kinases (MAPKs), in collagen-activated platelets. Neither the adenylate cyclase inhibitor SQ22536 nor the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one significantly reversed the Ir-6-mediated inhibition of collagen-induced platelet aggregation. Moreover, Ir-6 did not considerably diminish OH radical signals in collagen-activated platelets or Fenton reaction solution. At 2 mg/kg, Ir-6 markedly prolonged the bleeding time in experimental mice. In conclusion, Ir-6 plays a crucial role by inhibiting platelet activation through the inhibition of signaling pathways, such as the PLCγ2–PKC cascade and the subsequent suppression of Akt and MAPK activation, thereby ultimately inhibiting platelet aggregation. Therefore, Ir-6 is a potential therapeutic agent for preventing or treating thromboembolic disorders or disrupting the interplay between platelets and tumor cells, which contributes to tumor cell growth and progression.

Crystal structure and properties of (1,5-cyclooctadiene) (η5-pentamethylcyclopentadienyl) iridium(I) [Ir(cod)Cp*

Volatile iridium(I) complexes [Ir(cod)Cpx] (Cpx = pentamethylcyclopentadienyl Cp*, ethylcyclopentadienyl CpEt, cod = 1,5-cyclooctadiene) are synthesized and characterized by IR and NMR spectroscopy. The [Ir(cod)Cp*] complex is a solid and the [Ir(cod)CpEt] complex is a liquid (SATP). The XRD method is used to determine the structure of the [Ir(cod)Cp*] complex: chemical formula C18H27Ir, space group P21/c, a = 8,4418(2) A, b = 9,4764(3) A, c = 19.2682(5) A, β = 96.128(1) °, V = 1532.61(7) A3, Z = 4, d calc = 1.888 g/cm3, μ = 8.697 mm–1. The cyclopentadienyl ligand is η5-type coordinated; 1,5-cyclooctadiene have a cis-cis conformation and is η4-type coordinated. The thermal properties of the complexes are studied by thermogravimetry.

(Indenyl)iridacarborane (η5-indenyl)Ir(η-7,8-C2B9H11): synthesis, structure, and bonding

A reaction of iodide [(η5-indenyl)IrI2]n (1) with thallium dicarbollide Tl[Tl(η-7,8-C2B9H11)] leads to (indenyl)iridacarborane (η5-indenyl)Ir(η-7,8-C2B9H11) (2) in 32% yield. The X-ray diffraction study showed that in the structure of 2, the five-membered rings C5 and C2B3 have a cisoid conformation, in which the bridgehead carbon atoms of the indenyl ligand are arranged opposite to the carborane cage carbon atoms. The DFT calculations showed that the Ir—indenyl bond in compound 2 is weaker than the Ir—Cp bond in the complex (η-7,8-C2B9H11)IrCp.

A New Phenoxide Chelated IrIIIN-Heterocyclic Carbene Complex and Its Application in Reductive Amination Reactions

A new phenoxide chelated [Ir(NHC)Cp*Cl] (NHC = N-heterocyclic carbene; Cp* = pentamethylcyclopentadienyl) complex (3) has been prepared by reaction of [IrCp*Cl2]2 with an in situ prepared NHC–Ag complex in dichloromethane at ambient temperature. The IrIII complex was stable toward air and moisture and was fully characterized by 1H, 13C NMR, HRMS, and single-crystal X-ray diffraction. The new complex was found to be an active catalyst for transfer hydrogenative reductive amination under aqueous conditions with formate as hydrogen source as well as hydrogenative reductive amination reactions using H2. Various carbonyl compounds such as aliphatic and aromatic ketones and aldehydes were successfully reacted with amines to give new amines. In comparison with transfer hydrogenative reductive amination, the reductive amination with H2 is faster and permits higher molar ratios of the substrate to the catalyst (S/C).

Electrocatalytic carbon dioxide reduction by using cationic pentamethylcyclopentadienyl-iridium complexes with unsymmetrically substituted bipyridine ligands.

Eight [Ir(bpy)Cp*Cl](+) -type complexes (bpy= bipyridine, Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) containing differently substituted bipyridine ligands were synthesized and characterized. Cyclic voltammetry (CV) of the complexes in Ar-saturated acetonitrile solutions showed that the redox behavior of the complexes could be fine tuned by the electronic properties of the substituted bipyridine ligands. Further CV in CO2 -saturated MeCN/H2 O (9:1, v/v) solutions showed catalytic currents for CO2 reduction. In controlled potential electrolysis experiments (MeCN/MeOH (1:1, v/v), Eapp =-1.80 V vs Ag/AgCl), all of the complexes showed moderate activity in the electrocatalytic reduction of CO2 with good stability over at least 15 hours. This electrocatalytic process was selective toward formic acid, with only traces of dihydrogen or carbon monoxide and occasionally formaldehyde as byproducts. However, the turnover frequencies and current efficiencies were quite low. No direct correlation between the redox potentials of the complexes and their catalytic activity was observed.

Efficient production of hydrogen from formic acid using a covalent triazine framework supported molecular catalyst.

A heterogeneous molecular catalyst based on Ir(III) Cp* (Cp*=pentamethylcyclopentadienyl) attached to a covalent triazine framework (CTF) is reported. It catalyses the production of hydrogen from formic acid with initial turnover frequencies (TOFs) up to 27,000 h(-1) and turnover numbers (TONs) of more than one million in continuous operation. The CTF support, with a Brunauer-Emmett-Teller (BET) surface area of 1800 m(2) g(-1), was constructed from an optimal 2:1 ratio of biphenyl and pyridine carbonitrile building blocks. Biphenyl building blocks induce mesoporosity and, therefore, facilitate diffusion of reactants and products whereas free pyridinic sites activate formic acid towards β-hydride elimination at the metal, rendering unprecedented rates in hydrogen production. The catalyst is air stable, produces CO-free hydrogen, and is fully recyclable. Hydrogen production rates of more than 60 mol L(-1) h(-1) were obtained at high catalyst loadings of 16 wt % Ir, making it attractive towards process intensification.

Interfacial electron transfer in photoanodes based on phosphorus(v) porphyrin sensitizers co-deposited on SnO2 with the Ir(III)Cp* water oxidation precatalyst

The ability of PPors to photo-oxidize Ir(III)Cp* to Ir(IV)Cp* indicates that they are promising photoanode components.

Electronic effects of substituents on the stability of the iridanaphthalene compound [Ir[upper bond 1 start]Cp*{=C(OMe)CH=C(o-C6[upper bond 1 end]H4)(Ph)}(PMe3)]PF6.

Iridanaphthalene complexes are synthesized from the corresponding methoxy(alkenyl)carbeneiridium compounds. The electronic character of the substituents on the 6-position of the metallanaphthalene ring is crucial from the point of view of the stability of the iridanaphthalene, [Ir[upper bond 1 start]Cp*{=C(OMe)CH=C(o-C[upper bond 1 end]6H4)(Ph)}(PMe3)]PF6, vs. its transformation to the corresponding indanone derivatives. Stability studies of the iridanaphthalene compounds revealed that strong electron donor substituents (-OMe) stabilize the iridanaphthalene, while weak electron donor (-Me) and electron withdrawing (-NO2) groups favor the formation of indanone derivatives. Two possible indanone isomers can be obtained in the conversion of the unstable iridanaphthalene complexes and a mechanism for the formation of these isomers is proposed.

The Effects of Electron‐Donating Substituents on [Ir(bpy)Cp*Cl]+: Water Oxidation versus Ligand Oxidative Modifications

AbstractA series of [Ir(bpy)Cp*Cl]Cl (bpy: 2,2′‐bipyridine; Cp*: pentamethylcyclopentadienyl) complexes with 4,4′‐ and 6,6′‐substituents on the bipyridine ring were synthesized and used for water oxidation both electrochemically and with chemical oxidants. Under electrochemical water‐oxidation reaction (WOR) conditions at pH = 1, blue films were observed to deposit on the electrode surfaces for all of the complexes, without the detection of oxygen. For chemically driven WORs, three oxidants with different overpotentials and electron‐transfer kinetics led to very different behaviors. [Ru(bpy)3]3+ was shown to slowly oxidize the ligands without generating oxygen at pH = 3.7. With NaIO4 as the oxidant at neutral pH, oxygen generation was observed, but ligand oxidation was also seen for the complexes with electron‐donating substituents such as –OMe or –OH groups. With Ce4+ as the oxidant at pH = 1, a competition between water oxidation and ligand decomposition existed; less ligand decomposition was observed for catalysts that are more active for WOR. These results indicate the intricate nature of molecule water‐oxidation catalysts and their complex behaviors that are highly sensitive to water‐oxidation conditions.

Covalent Grafting of Organic–Inorganic Polyoxometalates Hybrids onto Mesoporous SBA-15: A Key Step for New Anchored Homogeneous Catalysts

Covalent grafting of heteropolyanions hybrids B,α-[As(III)W9O33{P(O)(CH2CH2CO2H)}2](5-) on 3-aminopropyl functionalized SBA-15 has been achieved through the formation of peptide bonds. The covalent link has been confirmed by using IR and (13)C CP MAS NMR spectroscopies. Electrostatic interactions between carboxylate and protonated amines have been discarded on the basis of the retention of POMs after repeated washings of the resulting material by ionic liquid (bmimCl). This is the first example of anchored monovacant polyoxometalates (POM) in which nucleophilic oxygen atoms are still available after incorporation into mesoporous supports. Further characterization of the textural properties of grafted materials has shown that they still retain an important mesoporosity, which is compatible with their potential use in heterogeneous catalysis. Such systems are thus interesting candidates for the preparation of anchored homogeneous catalysts in which the POMs would play the role of polydentate inorganic ligands for the active centers.

Catalyzed Tandem C–N/C–C Bond Formation for the Synthesis of Tricyclic Indoles using Ir(III) Pyrazolyl-1,2,3-Triazolyl Complexes

A series of new pyrazolyl-1,2,3-triazolyl N–N′ bidentate donor ligands (2a–c, 3a–d) were prepared via Cu(I)-catalyzed Huisgen cycloaddition reactions between 1-propargylpyrazoles and 4-substituted phenyl azides. The electron-withdrawing ability of the substituents follows the trend PhCH2 < p-CH3Ph < Ph < p-CF3Ph < p-NO2Ph, as illustrated in the gradual downfield shift of the 1,2,3-triazolyl-C4′ 13C NMR resonances. A series of Rh and Ir complexes containing these pyrazolyl-1,2,3-triazolyl or bis(pyrazol-1-yl)methane donor ligands of general formulae [Ir(N–N′)Cp*Cl]X (X = BArF4, BPh4; 5–8), [Rh(N–N′)Cp*Cl]X (X = BArF4, BPh4; 9–11), and [Rh(N–N′)(CO)2]BArF4 (13–16) (BArF4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) were synthesized and fully characterized. The solid-state structures of 5, 6a′, 6b, 7b, 8, 9, 10a, 10a′, 11, and 15c were determined by X-ray diffraction studies. As the electron-withdrawing strength of the phenylene substituent on the triazolyl ring is increased, the M–N3′(triazole) bond le...

ChemInform Abstract: Cp* Iridium Complexes Give Catalytic Alkane Hydroxylation with Retention of Stereochemistry.

AbstractThe hydroxylation of cycloalkanes (I) and (III) proceeds smoothly in the presence of an Ir—Cp* catalyst to give the product cycloalkanols (II) and (IV), resp., with retention of stereoselectivity.

Vapor pressure of some volatile iridium(I) compounds with carbonyl, acetylacetonate and cyclopentadienyl ligands

Abstract Volatile compounds of iridium(I): (acetylacetonato)(1,5-cyclooctadiene)iridium(I) Ir(acac)(cod), (methylcyclopentadienyl) (1,5-cyclooctadiene)iridium(I) Ir(Cp’)(cod), (pentamethylcyclopentadienyl)(dicarbonyl) iridium(I) Ir(Cp*)(CO)2 and (acetylacetonato)(dicarbonyl)iridium(I) Ir(acac)(CO)2 were synthesized and identified by means of element analysis, NMR-spectroscopy, mass spectrometry. Thermal properties in solid phase for synthesized iridium(I) complexes were studied by means of thermogravimetric analysis in inert atmosphere (He). By effusion Knudsen method with mass spectrometric registration of gas phase composition the temperature dependencies of saturated vapor pressure were measured for iridium(I) compounds and the thermodynamic characteristics of vaporization processes enthalpy ΔH T* and entropy ΔS T0 were determined. The energy of intermolecular interaction in the crystals of complexes was calculated.

Isolation and Crystal Structures of Both Enol and Keto Tautomer Intermediates in a Hydration of an Alkyne−Carboxylic Acid Ester Catalyzed by Iridium Complexes in Water

Hydration of tetrolic acid ethyl ester as an alkyne-carboxylic acid ester catalyzed by an Ir-aqua complex [Ir(III)Cp*(bpy)(OH2)]2+ (1, Cp* = eta5-C5Me5, bpy = 2,2'-bipyridine) in water provides ethyl acetoacetate as a beta-keto acid ester. We report the successful isolation of both an Ir-enol tautomer intermediate [IrIIICp*(bpy){CH3C(OH)=CC(O)OC2H5}]+ (2) and an Ir-keto tautomer intermediate [Ir(III)Cp*(bpy){CH3C(O)CHC(O)OC2H5}]+ (3) in the catalytic hydration by optimizing the conditions of the isolation, such as pH of the solution, reaction time, and selection of counteranions. The structures of the enol and keto complexes with characteristic Ir-(sp2carbon) bond and Ir-(sp3 carbon) bond, respectively, were unequivocally determined by X-ray analysis, IR, electrospray ionization mass spectrometry (ESI-MS), and NMR studies including 1H, 13C, distortionless enhancement by polarization transfer (DEPT) and correlation spectroscopy (COSY) experiments. It was confirmed that the hydration of tetrolic acid ethyl ester catalyzed by 2 or 3 as initial catalysts provides ethyl acetoacetate. Mechanism of the catalytic hydration of tetrolic acid ethyl ester as an alkyne-carboxylic acid ester is discussed based on isotopic labeling experiments with the Ir-enol and Ir-keto tautomers.

Structural comparison of (pentamethylcyclopentadienyl)iridium(III) azido complexes containing potentially N, S-bidentate N-heterocyclic thiolates: 2- or 8-quinolinethiolate and benzimidazole-2-thiolate

The crystal structures of mononuclear (azido)(pentamethylcyclopentadienyl)iridium(III) complexes bearing 2- or 8-quinolinethiolate ( n-Sqn −), [Cp ∗Ir(N 3)( n-Sqn)] { n = 2 ( 1) or 8 ( 2); Cp ∗ = η 5-C 5Me 5} have been determined by X-ray analysis. The 2-Sqn complex, 1, acquires severe steric strains in the four-membered κ 2 N, S chelate ring, while the 8-Sqn isomer, 2, forms a strain-free five-membered planar κ 2 N, S chelate ring. It has also been revealed that the corresponding benzimidazole-2-thiolate (Hbimt −) complex, which was obtained similarly to the above n-Sqn complexes from [Cp ∗Ir(N 3) 2] 2 and Na(Hbimt), takes an unsymmetrical dinuclear structure bridged by two Hbimt − ligands with different bonding modes, [Cp ∗Ir(N 3){ μ( S: N 1)-Hbimt}{ μ( S: S)-Hbimt}Ir(N 3)Cp ∗] · MeOH ( 3).

Zero-Point Corrections and Temperature Dependence of HD Spin−Spin Coupling Constants of Heavy Metal Hydride and Dihydrogen Complexes Calculated by Vibrational Averaging

Vibrational corrections (zero-point and temperature dependent) of the H-D spin-spin coupling constant J(HD) for six transition metal hydride and dihydrogen complexes have been computed from a vibrational average of J(HD) as a function of temperature. Effective (vibrationally averaged) H-D distances have also been determined. The very strong temperature dependence of J(HD) for one of the complexes, [Ir(dmpm)Cp*H2]2 + (dmpm = bis(dimethylphosphino)methane) can be modeled simply by the Boltzmann average of the zero-point vibrationally averaged JHD of two isomers. For this complex and four others, the vibrational corrections to JHD are shown to be highly significant and lead to improved agreement between theory and experiment in most cases. The zero-point vibrational correction is important for all complexes. Depending on the shape of the potential energy and J-coupling surfaces, for some of the complexes higher vibrationally excited states can also contribute to the vibrational corrections at temperatures above 0 K and lead to a temperature dependence. We identify different classes of complexes where a significant temperature dependence of J(HD) may or may not occur for different reasons. A method is outlined by which the temperature dependence of the HD spin-spin coupling constant can be determined with standard quantum chemistry software. Comparisons are made with experimental data and previously calculated values where applicable. We also discuss an example where a low-order expansion around the minimum of a complicated potential energy surface appears not to be sufficient for reproducing the experimentally observed temperature dependence.