Ir Cl Research Articles

A Kinetic and Mechanistic Study of Ir (III)-Catalyzed Oxidation of Methionine by HCF (III) in an Aqueous Alkaline Medium

Introduction: The kinetic study of Ir (III) chloride-catalyzed oxidation of methionine by hexacyanoferrate (abbreviated as HCF) III ions in aqueous alkaline medium was performed spectrophotometrically at constant ionic strength of 0.5 moldm-3 and temperature of 35±0.10C. Method: The progress of the reaction was found to be first-order rate dependence kinetics with respect to [HCF (III)], [OH-], and [IrCl3]. The rate of reaction was found to decrease with an increased concentration of methionine. The ionic strength of the reaction mixture showed a positive salt effect on the reaction rate. Different activation parameters were also evaluated by studying the reaction at four different temperatures. The stoichiometry of the reaction showed Methionine: HCF (III) = 1:4. Result: The oxidation product of the reaction was found to be methionine sulphone, which was identified by an organic solvent method and IR Spectroscopy. Further, a suitable mechanism was proposed to explain all the experimental results. Conclusion: It is assumed that the reaction proceeded through complex formation between substrate (abbreviated) and iridium trichloride. A rate law was derived, which verified the results. CH3-S-(CH2)2-CH (NH2)-COO- + 4HCF (III) Ir (III), H2O CH3-SO2-(CH2)2-CH- (NH2)-COO- + 4HCF (II) result: 1.Methionine sulphone was found to be the main product of oxidation was identified using an organic solvent method and IR Spectroscopy. A suitable mechanism has been proposed to explain all the experimental results. It is assumed that reaction proceeds through complex formation between substrate (abbreviated) and iridium trichloride. A rate law has been derived which verifies the results. CH3 –S-(CH2)2-CH (NH2) – COO- + 4HCF (III) □(→┴(Ir(III),H2O) ) CH3-SO2-(CH2)2-CH (NH2)-COO- + 4HCF (II) 2. Degradation kinetic is anticipated to follow the first order kinetics at lower concentration. 3. The catalytic system can be recycled and reused without loss of activity. 4. The anticipated easy recovery of catalyst from the reaction mixture shows another positive signigficance.

Electrocatalytic Transfer Hydrogenation of 1-Octene with [(tBuPCP)Ir(H)(Cl)] and Water.

Electrocatalytic hydrogenation of 1-octene as non-activated model substrate with neutral water as H-donor is reported, using [(tBuPCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96% and a kobs of 87 s-1. Cyclic voltammetry with 1 revealed that two subsequent reductions trigger the elimination of Cl- and afford the highly reactive anionic Ir(I) hydride complex [(tBuPCP)Ir(H)]- (2), a previously merely proposed intermediate for which we now report first experimental data by mass spectrometry. In absence of alkene, the stoichiometric electrolysis of 1 in THF with water selectively affords the Ir(III) dihydride complex [(tBuPCP)Ir(H)2] (3) in 88% FE from the reaction of 2 with H2O. Complex 3 then hydrogenates the alkene in classical fashion. The presented electro-hydrogenation works with extremely high FE, because the iridium hydrides are water stable, which prevents H2 formation. Even in strongly alkaline conditions (Bu4NOH added), the electro-hydrogenation of 1-octene with 1 also proceeds cleanly (89% FE), suggesting a highly robust process that may rely on H2O activation, reminiscent to transfer hydrogenation pathways, instead of classical H+ reduction. DFT calculations confirmed oxidative addition of H2O as a key step in this context.

Electrocatalytic Transfer Hydrogenation of 1‐Octene with [(tBuPCP)Ir(H)(Cl)] and Water

Electrocatalytic hydrogenation of 1‐octene as non‐activated model substrate with neutral water as H‐donor is reported, using [(tBuPCP)Ir(H)(Cl)] (1) as the catalyst, to form octane with high faradaic efficiency (FE) of 96% and a kobs of 87 s–1. Cyclic voltammetry with 1 revealed that two subsequent reductions trigger the elimination of Cl– and afford the highly reactive anionic Ir(I) hydride complex [(tBuPCP)Ir(H)]– (2), a previously merely proposed intermediate for which we now report first experimental data by mass spectrometry. In absence of alkene, the stoichiometric electrolysis of 1 in THF with water selectively affords the Ir(III) dihydride complex [(tBuPCP)Ir(H)2] (3) in 88% FE from the reaction of 2 with H2O. Complex 3 then hydrogenates the alkene in classical fashion. The presented electro‐hydrogenation works with extremely high FE, because the iridium hydrides are water stable, which prevents H2 formation. Even in strongly alkaline conditions (Bu4NOH added), the electro‐hydrogenation of 1‐octene with 1 also proceeds cleanly (89% FE), suggesting a highly robust process that may rely on H2O activation, reminiscent to transfer hydrogenation pathways, instead of classical H+ reduction. DFT calculations confirmed oxidative addition of H2O as a key step in this context.

Boosting Effect of Sterically Protected Glucosyl Substituents in Formic Acid Dehydrogenation by Iridium(III) 2-Pyridineamidate Catalysts.

[Cp*Ir(R-pica)Cl] (Cp* = pentamethylcyclopentadienyl anion, pica = 2-picolineamide) complexes bearing carbohydrate substituents on the amide nitrogen atom (R = methyl-β-D-gluco-pyranosid-2-yl, 1; methyl-3,4,6-tri-O-acetyl-β-D-glucopyranosid-2-yl, 2) were tested as catalysts for formic acid dehydrogenation in water. TOFMAX values over 12000 h-1 and 50000 h-1 were achieved at 333 K for 1 and 2, respectively, with TON values over 35000 for both catalysts. Comparison with the simpler cyclohexyl-substituted analogue (3) indicated that glucosyl-based complexes are much better performing under the same experimental conditions (TOFMAX = 5144 h-1, TON = 5000 at pH 2.5 for 3) owing to a lower tendency to isomerize to the less active k2-N,O isomer upon protonation. The 5-fold increase in TOFMAX observed for 2 with respect to 1 is reasonably due to an optimal steric protection by the acetyl substituent, which may prevent unproductive inner-sphere reactivity. These results showcase a powerful strategy for the inhibition of the common deactivation pathways of [Cp*Ir(R-pica)X] catalysts for FA dehydrogenation, paving the way for the development of better performing hydrogen storage systems.

Catalytic hydrosilylation of 1,3-diynes towards (E)-2-silylbut-1-en-3-ynes, (E,E)-2,3-disilylbuta-1,3-dienes and (E,E)-2-silyl1-3-silyl2buta-1,3-dienes

Hydrosilylation of 1,3-diynes produced (E)-2-silylbut-1-en-3-ynes, (E,E)-2,3-disilylbuta-1,3-dienes, and (E,E)-2-silyl1-3-silyl2buta-1,3-dienes, which due to their complex structure and susceptibility to modification could be used in the preparation of drugs or natural compounds. The application of Pt2(dvs)3, PtO2, or [Ir(cod)Cl]2 (at room temperature or 40 ℃) allowed us to obtain (E)-2-silylbut-1-en-3-ynes. Their further modification in the presence of Pt2(dvs)3 or Pt(en)Cl2 (at 140 °C) led to the exclusive formation of (E,E)-2,3-disilylbuta-1,3-dienes, and (E,E)-2-silyl1-3-silyl2buta-1,3-dienes (a new family of compounds not yet obtained by other methods). For the first time, Pt(en)Cl2 was found to be effective in the hydrosilylation of 1,3-diynes, while [Ir(cod)Cl]2 compared to the literature, surprisingly gave (E)-2-silylbut-1-en-3-ynes instead of (E)-4-silylbut-1-en-3-ynes. Moreover, the first crystal structure of (E,E)-2,3-disilylbuta-1,3-diene was reported.

(Pentamethylcyclopentadienyl)chloridoiridium(III) Complex Bearing Bidentate Ph2PCH2CH2SPh-κP,κS Ligand.

The (pentamethylcyclopentadienyl)chloridoiridium(III) complex bearing a κP,κS-bonded Ph2PCH2CH2SPh ligand ([Ir(η5-C5Me5)Cl(Ph2P(CH2)2SPh-κP,κS)]PF6, (1)] was synthesized and characterized. Multinuclear (1H, 13C and 31P) NMR spectroscopy was employed for the determination of the structure. Moreover, SC-XRD confirmed the proposed structure belongs to the "piano stool" type. The Hirshfeld surface analysis outlined the most important intermolecular interactions in the structure. The crystallographic structure was optimized at the B3LYP-D3BJ/6-311++G(d,p)(H,C,P,S,Cl)/LanL2DZ(Ir) level of theory. The applicability of this level was verified through a comparison of experimental and theoretical bond lengths and angles, and 1H and 13C NMR chemical shifts. The Natural Bond Orbital theory was used to identify and quantify the intramolecular stabilization interactions, especially those between donor atoms and Ir(III) ions. Complex 1 was tested on antitumor activity against five human tumor cell lines: MCF-7 breast adenocarcinoma, SW480 colon adenocarcinoma, 518A2 melanoma, 8505C human thyroid carcinoma and A253 submandibular carcinoma. Complex 1 showed superior antitumor activity against cisplatin-resistant MCF-7, SW480 and 8505C cell lines. The mechanism of tumoricidal action on 8505C cells indicates the involvement of caspase-induced apoptosis, accompanied by a considerable reduction in ROS/RNS and proliferation potential of treated cells.

Abstract 4488: Newly developed organoiridium(III) complexes containing N,P-ligands possess antiproliferative activity in selected cancer cell lines

Abstract In conventional cancer treatment, platinum-based cytostatics are considered as standard therapy; however, they possess severe side effects. This fact leads to a constant effort to develop new non-platinum metallodrugs with different mechanism of action (MoA). In our study we developed new half-sandwich organoiridium(III) complexes, of general formulas [Ir(η5-Cp*)Cl(LNP)]PF6 (1-3) and [Ir(η5-Cpph)Cl(LNP)]PF6 (4-6) involving three different N,P-donor phosphinoalkylamines (LNP), which we tested on 2D and 3D cancer models; HCp* = pentamethylcyclopentadiene, HCpph= (2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)benzene. The most effective complexes 3 and 6 bearing 3-(diphenylphosphanyl)propan-1-amine had the highest cytotoxic effect against various cancer cell lines (THP-1, HeLa, SW982, A549, MOR) including a cisplatin-resistant lung carcinoma cell line (MOR/CPR) with IC50 values between 3.1 and 9.1 μM for specific cell lines. The cytotoxic effect was further demonstrated on 3D spheroids of lung cancer cells that revealed anti-cancer and anti-migration potential of complexes 3 and 6. Cell cycle and cell death analysis showed a different mechanism compared to the effect of cisplatin. Moreover, complex 3 did not decrease cell viability of non-cancerous cells (peripheral blood mononuclear cells and porcine chondrocytes) under 50% at a concentration of 20 µM. In addition, we report for the first time that organoiridium complexes showed high cytotoxic activity on cancer cell lines, including cisplatin-resistant cell line, with different MoA from cisplatin. They trigger expression of stress-related genes associated with oxidative stress, DNA damage, and endoplasmic reticulum stress and, moreover, complex 3 showed cytotoxic selectivity towards cancer cells. This work was supported by the Czech health research council of the Ministry of Health of the Czech Republic (AZV Project NU22-08-00236). Citation Format: Renata Hezova, Jan Hosek, Nicol Strakova, Pavlina Simeckova, Josef Masek, Simona Kajabova, Pavel Starcha. Newly developed organoiridium(III) complexes containing N,P-ligands possess antiproliferative activity in selected cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4488.

Upgrading Ethanol to n-Butanol in the Presence of Carbonate Catalyzed by a Cp*Ir Complex Bearing a Functional 2,2'-Carbonylbibenzimidazole Ligand.

Upgrading ethanol to n-butanol as biofuels is an important topic for sustainable chemistry. Herein, a Cp*Ir complex bearing a functional 2,2'-carbonylbibenzimidazole ligand [Cp*Ir(2,2'-COBiBzImH2)Cl][Cl] was designed and synthesized. In the presence of a catalyst (0.1 mol %) and Cs2CO3 (6 mol %), the highest yield of updated n-butanol is up to 37% with 80% selectivity. NH units in the ligand are crucially important for the catalytic activity of the iridium complex.

Ir(III) Half-Sandwich Photosensitizers with a π-Expansive Ligand for Efficient Anticancer Photodynamic Therapy.

One approach to reduce the side effects of chemotherapy in cancer treatment is photodynamic therapy (PDT), which allows spatiotemporal control of the cytotoxicity. We have used the strategy of coordinating π-expansive ligands to increase the excited state lifetimes of Ir(III) half-sandwich complexes in order to facilitate the generation of 1O2. We have obtained derivatives of formulas [Cp*Ir(C∧N)Cl] and [Cp*Ir(C∧N)L]BF4 with different degrees of π-expansion in the C∧N ligands. Complexes with the more π-expansive ligand are very effective photosensitizers with phototoxic indexes PI > 2000. Furthermore, PI values of 63 were achieved with red light. Time-dependent density functional theory (TD-DFT) calculations nicely explain the effect of the π-expansion. The complexes produce reactive oxygen species (ROS) at the cellular level, causing mitochondrial membrane depolarization, cleavage of DNA, nicotinamide adenine dinucleotide (NADH) oxidation, as well as lysosomal damage. Consequently, cell death by apoptosis and secondary necrosis is activated. Thus, we describe the first class of half-sandwich iridium cyclometalated complexes active in PDT.

General Ir-Catalyzed N-H Insertions of Diazomalonates into Aliphatic and Aromatic Amines.

A general N-H insertion reactivity of acceptor-acceptor diazo malonate reagents is reported using [Ir(cod)Cl]2 as catalyst. A large range of amines, primary and secondary, aliphatic and aromatic, is possible. Mild temperatures, perfect substrate/reactant stoichiometry, and good functional group compatibility render the process particularly attractive for the (late-stage) functionalization of amines.

BICAAC-Derived Covalent and Cationic Ir(I) Complexes: Application of Ir(BICAAC)Cl(COD) Complexes as Catalysts for Transfer Hydrogenation and Hydrosilylation Reactions.

The ambiphilic bicyclic (alkyl)(amino)carbenes (Me/iPrBICAAC) upon reaction with [IrCl(COD)]2 smoothly afford mononuclear Ir(I) complexes that have been spectroscopically and structurally characterized. These complexes exhibit good catalytic activity for transfer hydrogenation (TH) of 4-chlorobenzaldehyde using isopropyl alcohol (iPrOH), with turnover frequency values ranging between 6269 and 8093 h-1. Choosing the covalent complex Ir(MeBICAAC)Cl(COD) as a catalyst, a wide array of carbonyls and imines functionalized with electron-withdrawing and electron-donating substituents have been surveyed and afforded their reduced products in moderate-to-good yields. No detachment of the BICAAC unit from the Ir center was observed upon prolonged heating of Ir(MeBICAAC)Cl(COD) in toluene-d8 or isopropyl alcohol-d8, which evidenced good thermal stability of the catalyst. Complex Ir(MeBICAAC)Cl(COD) was also found to be catalytically active for the hydrosilylation of a variety of aldehydes using triethylsilane (Et3SiH).

Controlled cluster expansion at a Zintl cluster surface

AbstractReaction of the tris‐hypersilyl nonagermanide Zintl cluster salt, K[Ge9(Hyp)3] (Hyp=Si(SiMe3)3) with [Rh(η2,η2‐L)Cl]2 (L=1,5‐cyclooctadiene, COD; norbornadiene, NBD) afforded eleven‐ and twelve‐vertex homo‐multimetallic clusters by cluster core expansion. Using a stepwise procedure, starting from the Zintl cluster [Rh(COD){Ge9(Hyp)3}] and [Ir(COD)Cl]2, this methodology was expanded for the synthesis of eleven‐vertex hetero‐multimetallic clusters. A mechanism for the formation of these first examples of closo eleven‐vertex Zintl clusters is proposed, informed by density functional theory calculations.

Controlled cluster expansion at a Zintl cluster surface.

Reaction of the tris-hypersilyl nonagermanide Zintl cluster salt, K[Ge9 (Hyp)3 ] (Hyp=Si(SiMe3 )3 ) with [Rh(η2 ,η2 -L)Cl]2 (L=1,5-cyclooctadiene, COD; norbornadiene, NBD) afforded eleven- and twelve-vertex homo-multimetallic clusters by cluster core expansion. Using a stepwise procedure, starting from the Zintl cluster [Rh(COD){Ge9 (Hyp)3 }] and [Ir(COD)Cl]2 , this methodology was expanded for the synthesis of eleven-vertex hetero-multimetallic clusters. A mechanism for the formation of these first examples of closo eleven-vertex Zintl clusters is proposed, informed by density functional theory calculations.

XPS and HR TEM Elucidation of the Diversity of Titania-Supported Single-Site Ir Catalyst Performance in Spin-Selective Propene Hydrogenation

Immobilized [Ir(COD)Cl]2-Linker/TiO2 catalysts with linkers containing Py, P(Ph)2 and N(CH3)2 functional groups were prepared. The catalysts were tested via propene hydrogenation with parahydrogen in a temperature range from 40 °C to 120 °C which was monitored via NMR. The catalytic behavior of [Ir(COD)Cl]2-Linker/TiO2 is explained on the basis of quantitative and qualitative XPS data analysis performed for the catalysts before and after the reaction at 120 °C. It is shown that the temperature dependence of propene conversion and the enhancement of the NMR signal are explained via a combination of the stabilities of both the linker and immobilized [Ir(COD)Cl]2 complex. It is demonstrated that the N(CH3)2-linker is the most stable at the surface of TiO2 under used reaction conditions. As a result, only this sample shows a rise in the enhancement of the NMR signal in the 100–120 °C temperature range.

Evoking Ferroptosis by Synergistic Enhancement of a Cyclopentadienyl Iridium-Betulin Immune Agonist.

Ferroptosis is a form of programmed cell death driven by iron-dependent lipid peroxidation (LPO) with the potential for antitumor immunity activation. In this study, a nonferrous cyclopentadienyl metal-based ferroptosis inducer [Ir(Cp*)(Bet)Cl]Cl (Ir-Bet) was developed by a metal-ligand synergistic enhancement (MLSE) strategy involving the reaction of [Ir(Cp*)Cl]2 Cl2 with the natural product Betulin. The fusion of Betulin with iridium cyclopentadienyl (Ir-Cp*) species as Ir-Bet not only tremendously enhanced the antiproliferative activity toward cancer cells, but also activated ferritinophagy for iron homeostasis regulation by PI3K/Akt/mTOR cascade inhibition with a lower dosage of Betulin, and then evoked an immune response by nuclear factor kappa-B (NF-κB) activation of Ir-Cp* species. Further immunogenic cell death (ICD) occurred by remarkable ferroptosis through glutathione (GSH) depletion, glutathione peroxidase 4 (GPX4) deactivation and ferritinophagy. An in vivo vaccination experiment demonstrated desirable antitumor and immunogenic effects of Ir-Bet by increasing the ratio of cytotoxic T cells (CTLs)/regulatory T cells (Tregs).

Evoking Ferroptosis by Synergistic Enhancement of a Cyclopentadienyl Iridium‐Betulin Immune Agonist

AbstractFerroptosis is a form of programmed cell death driven by iron‐dependent lipid peroxidation (LPO) with the potential for antitumor immunity activation. In this study, a nonferrous cyclopentadienyl metal‐based ferroptosis inducer [Ir(Cp*)(Bet)Cl]Cl (Ir‐Bet) was developed by a metal‐ligand synergistic enhancement (MLSE) strategy involving the reaction of [Ir(Cp*)Cl]2Cl2 with the natural product Betulin. The fusion of Betulin with iridium cyclopentadienyl (Ir‐Cp*) species as Ir‐Bet not only tremendously enhanced the antiproliferative activity toward cancer cells, but also activated ferritinophagy for iron homeostasis regulation by PI3K/Akt/mTOR cascade inhibition with a lower dosage of Betulin, and then evoked an immune response by nuclear factor kappa‐B (NF‐κB) activation of Ir‐Cp* species. Further immunogenic cell death (ICD) occurred by remarkable ferroptosis through glutathione (GSH) depletion, glutathione peroxidase 4 (GPX4) deactivation and ferritinophagy. An in vivo vaccination experiment demonstrated desirable antitumor and immunogenic effects of Ir‐Bet by increasing the ratio of cytotoxic T cells (CTLs)/regulatory T cells (Tregs).

Iridium metal complex targeting oxidation resistance 1 protein attenuates spinal cord injury by inhibiting oxidative stress-associated reactive oxygen species

Oxidative stress is a key factor leading to profound neurological deficits following spinal cord injury (SCI). In this study, we present the development and potential application of an iridium (iii) complex, (CpxbiPh) Ir (N^N) Cl, where CpxbiPh represents 1-biphenyl-2,3,4,5-tetramethyl cyclopentadienyl, and N^N denotes 2-(3-(4-nitrophenyl)-1H-1,2,4-triazol-5-yl) pyridine chelating agents, to address this challenge through a mechanism governed by the regulation of an antioxidant protein. This iridium complex, IrPHtz, can modulate the Oxidation Resistance 1 (OXR1) protein levels within spinal cord tissues, thus showcasing its antioxidative potential. By eliminating reactive oxygen species (ROS) and preventing apoptosis, the IrPHtz demonstrated neuroprotective and neural healing characteristics on injured neurons. Our molecular docking analysis unveiled the presence of π stacking within the IrPHtz-OXR1 complex, an interaction that enhanced OXR1 expression, subsequently diminishing oxidative stress, thwarting neuroinflammation, and averting neuronal apoptosis. Furthermore, in in vivo experimentation with SCI-afflicted mice, IrPHtz was efficacious in shielding spinal cord neurons, promoting their regrowth, restoring electrical signaling, and improving motor performance. Collectively, these findings underscore the potential of employing the iridium metal complex in a novel, protein-regulated antioxidant strategy, presenting a promising avenue for therapeutic intervention in SCI.

Development of a Highly In Vivo Efficacious Dual Antitumor and Antiangiogenic Organoiridium Complex as a Potential Anti-Lung Cancer Agent.

While the phenomenal clinical success of blockbuster platinum (Pt) drugs is highly encouraging, the inherent and acquired resistance and dose-limiting side effects severely limit their clinical application. To find a better alternative with translational potential, we synthesized a library of six organo-IrIII half-sandwich [(η5-CpX)Ir(N∧N)Cl]+-type complexes. In vitro screening identified two lead candidates [(η5-CpXPh)Ir(Ph2Phen)Cl]+ (5, CpXPh = tetramethyl-phenyl-cyclopentadienyl and Ph2Phen = 4,7-diphenyl-1,10-phenanthroline) and [(η5-CpXBiPh)Ir(Ph2Phen)Cl]+ (6, CpXBiPh = tetramethyl-biphenyl-cyclopentadienyl) with nanomolar IC50 values. Both 5 and 6 efficiently overcame Pt resistance and presented excellent cancer cell selectivity in vitro. Potent antiangiogenic properties of 6 were demonstrated in the zebrafish model. Satisfyingly, 6 and its nanoliposome Lipo-6 presented considerably higher in vivo antitumor efficacy as compared to cisplatin, as well as earlier reported IrIII half-sandwich complexes in mice bearing the A549 non-small lung cancer xenograft. In particular, complex 6 is the first example of this class that exerted dual in vivo antiangiogenic and antitumor properties.

Synthesis, Structure, and Catalytic Activity of Cyclometalated Iridium Complexes with a Bidentate POC Ligand

AbstractSynthesis, characterization and catalytic activity of cyclometalated iridium complexes with a bidentate POC ligand is presented. Metalation of POC‐H (di‐tert‐butyl(phenoxy)phosphane) with [Ir(COD)Cl]2 proceeded rapidly at room temperature and afforded mixture of (POC)(POC‐H)IrHCl (1 a) and (POC)(COD)IrHCl (1 b), from which complexes (POC)(L)IrHCl where L=PPh3 (1 c), bipyridine (1 d) and [2,2′‐bipyridine]‐6,6′‐diol (1 e) were prepared through ligand exchange. The compounds were tested in acceptorless dehydrogenation of 1‐phenylethanol and transfer dehydrogenation of ethanol in a context of comparison with pincer counterparts (POCOP)IrHCl and (PCN)IrHCl. An attempt to prepare a dihydride complex from 1 e led to dimeric complex [(POC)(bipy‐diol−)IrH]2 (3) that could explain the low activity of 1 e. DFT studies provided insight into POC‐H vs POCOP‐H metalation mechanism.

Unusual formation of Ir(III) complexes with non‐symmetrical NacNac ligands: Synthesis, characterization, and evaluation of catalytic activity in transfer hydrogenation reduction reactions

A new type of trans‐dichloro‐Ir(III) complexes derived from non‐symmetrical NacNac‐type ligands was unexpectedly obtained as the main reaction product from the former ligands and the dimeric species [Ir(COD)Cl2]. One equivalent of LH was reacted with an excess of [Ir(COD)Cl]2 in dichloromethane or toluene as solvent and at room temperature. The general formula of the product is [IrCl2(COD)L] and was isolated as a sole product instead of the expected Ir(I) compound [Ir(COD)L]; all the new Ir(III) were prepared in high yields as microcrystalline solids. They were all stable under laboratory atmosphere, lasting for weeks in solution and for months in solid state. The structure of each compound was examined by 1D and 2D nuclear magnetic resonance (NMR) and high‐resolution mass spectrometry (HRMS). Complex 1k was selected for an X‐ray diffraction study. Finally, an evaluation was made of the catalytic activity of all complexes in the transfer hydrogenation reaction of ketones and imines.