Ligands L1 Research Articles

A Phosphonate Substituent in a 1,10‐Phenanthroline Ligand Boosts Light‐Driven Catalytic Water Oxidation Performance Sensitized by Ruthenium Chromophores

AbstractA series of new Ruthenium(II) complexes based on the (1,10‐phenanthrolin‐5‐yl)diethyl phosphonate ligand L2 and their corresponding phosphonic acid along with reference compounds are synthesized in order to evaluate the influence of the phosphonate substitution on the catalytic performance of such molecules. UV‐vis absorption and emission spectroscopy show, that introduction of a phosphonate moiety into the periphery of the phenanthroline ligand does not alter the photophysical properties of the complex. In contrast, the electrochemical features of all compounds are affected upon respective functionalization compared to the reference molecule [Ru(bpy)3](PF6)2 in aqueous medium. Photostability tests in water or in water/persulfate show a dependency of the stability towards photodecomposition on quenching efficiency with persulfate anion. The lower quenching efficiency thus leads to increased stability based on the negative charge of the phosphonate moiety in 2 and P1 in aqueous medium following a quenching efficiency trend of [Ru(bpy)3](PF6)2>1>2>P1. Photocatalytic water oxidation using [Ru(dpp)(pic)2](PF6)2 reveals that compound 1 and [Ru(bpy)3](PF6)2 doe not exhibit any activity under the utilized conditions, P1 shows a negligible TON of 7, whereas compound 2 reaches a TON of 140 after 1 h. This fact highlights that the redox potential is not the sole driver in the catalytic cycle and accentuates the importance of different criteria determining the suitability of photosensitizers in light‐driven water oxidation, such as light absorption, redox potential of the RuIII/RuII event, photostability towards and quenching efficiency with the sacrificial agent.

Azide-Alkyne "Click" Reaction in Water Using Parts-Per-Million Amine-Functionalized Azoaromatic Cu(I) Complex as Catalyst: Effect of the Amine Side Arm.

A series of Cu(II) complexes, 1-4 and 6, were synthesized through a reaction of amine-functionalized pincer-like ligands, HL1,2, La,b, and a bidentate ligand L1 with CuCl2·2H2O. The chemical reduction of complex 1 using 1 equiv of sodium l-ascorbate resulted in a dimeric Cu(I) complex 5 in excellent yield. All of the complexes, 1-6, were thoroughly characterized using various physicochemical characterization techniques, single-crystal X-ray structure determination, and density functional theory calculations. Ligands HL1,2 and La,b behaved as tridentated donors by the coordination of the amine side arm in their respective Cu(II) complexes, and the amine side arm remained as a pendant in Cu(I) complexes. All of these complexes (1-6) were explored for copper(I)-catalyzed 1,3-dipolar azide-alkyne cycloaddition (CuAAC) reaction at room temperature in water under air. Complex 5 directly served as an active catalyst; however, complexes 1-4 and 6 required 1 equiv of sodium l-ascorbate to generate their corresponding active Cu(I) catalyst. It has been observed that azo-based ligand-containing Cu(I)-complexes are air-stable and were highly efficient for the CuAAC reaction. The amine side arm in the ligand backbone has a dramatic role in accelerating the reaction rate. Mechanistic investigations showed that the alkyne C-H deprotonation was the rate-limiting step and the pendant amine side arm intramolecularly served as a base for Cu-coordinated alkyne deprotonation, leading to the azide-alkyne 2 + 3 cycloaddition reaction. Thus, variation of the amine side arm in complexes 1-4 and use of the most basic diisopropyl amine moiety in complex 4 has resulted in an unique amine-functionalized azoaromatic Cu(I) system for CuAAC reaction upon sodium l-ascorbate reduction. The complex 4 has shown excellent catalysis at its low parts-per-million level loading in water. The catalytic protocol was versatile and exhibited very good functional group tolerance. It was also employed efficiently to synthesize a number of useful functional triazoles having medicinal, catalytic, and targeting properties.

Synthesis, Characterization and Biological Screening of Alkylene Dithiophosphate Derivatives of Macrocyclic Complexes of Pb (II)

Alkylenedithiophosphate derivatives of macrocyclic complexes of Pb (II), having N4S4 potential donors, of the general formula, [Pb(L){S2P(OR)2}2] where L=macrocyclic ligands L1, L2, L3, L4 and L5; R= C2H5-, C3H7n or C3H7i have been synthesized from the reaction of [Pb(L)X2(where X= Clˉ, NO3ˉ or CH3COOˉ) with sodium Alkylenedithiophosphate in 1:2 molar ratios in THF. These complexes have been characterized by elemental analysis, molar conductance, molecular weight determinations, IR, 1H, 13C NMR. Macrocyclic Complexes of Pb (II) derivatives have been studied by screening them Aspergillus flavus, Fusarium oxysporum, Alternaria alternata and bacteria like Salmonella typhi and Bacillus subtili. Alkylenedithiophosphate derivatives were found to be more fungitoxic and antibacterial than their corresponding macrocyclic complexes.

Cytotoxic Ruthenium(II) Complexes of Pyrazolylbenzimidazole Ligands That Inhibit VEGFR2 Phosphorylation.

Eight new ruthenium(II) complexes of N,N-chelating pyrazolylbenzimidazole ligands of the general formula [RuII(p-cym)(L)X]+ [where the ligand L is 2-(1H-pyrazol-1-yl)-1H-benzo[d]imidazole (L1) substituted at the 4 position of the pyrazole ring by Cl (L2), Br (L3), or I (L4) and X = Cl- and I-] were synthesized and characterized using various analytical techniques. Complexes 1 and 3 were also characterized by single-crystal X-ray crystallography, and they crystallized as a monoclinic crystal system in space groups P21/n and P21/c, respectively. The complexes display good solution stability at physiological pH 7.4. The iodido-coordinated pyrazolylbenzimidazole ruthenium(II) p-cymene complexes (2, 4, 6, and 8) are more resistant toward hydrolysis and have less tendency to form monoaquated complexes in comparison to their chlorido analogues (1, 3, 5, and 7). The halido-substituted 2-(1H-pyrazol-1-yl)-1H-benzo[d]imidazole ligands, designed as organic-directing molecules, inhibit vascular endothelial growth factor receptor 2 (VEGFR2) phosphorylation. In addition, the ruthenium(II) complexes display a potential to bind to DNA bases. The cytotoxicity profile of the complexes (IC50 ca. 9-12 μM for 4-8) against the triple-negative breast cancer cells (MDA-MB-231) show that most of the complexes are efficient. The lipophilicity and cellular accumulation data of the complexes show a good correlation with the cytotoxicity profile of 1-8. The representative complexes 3 and 7 demonstrate the capability of arresting the cell cycle in the G2/M phase and induce apoptosis. The inhibition of VEGFR2 phosphorylation with the representative ligands L2 and L4 and the corresponding metal complexes 3 and 7 in vitro shows that the organic-directing ligands and their complexes inhibit VEGFR2 phosphorylation. Besides, L2, L4, 3, and 7 inhibit the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and proto-oncogene tyrosine-protein kinase (Src), capable of acting downstream of VEGFR2 as well as independently. Compounds L2, L4, 3, and 7 have a lesser effect on ERK1/2 and more prominently affect Src phosphorylation. We extended the study for L2 and 3 in the Tg(fli1:gfp) zebrafish model and found that L2 is more effective in vivo compared to 3 in inhibiting angiogenesis.

Construction of 1D and 3D rare crystalline infinite silver alkynyl assemblies using dicarboxylic acid as co-ligand and their luminescence properties

Two crystalline silver alkynyl assemblies, namely, [Ag6(tBuCC)4 L1]n (1), [Ag10(tBuCC)6(L2)2]n (2) (H2L1 = 1,8-naphthalene dicarboxylic acid and H2L2 = 1,4-naphthalene dicarboxylic acid) have been obtained by the reaction of polymeric [tBuCCAg]n with silver salts and dicarboxylic acids under mild solvothermal conditions. Compounds 1 and 2 are coordination polymers of irregular silver alkynyl clusters. 1 is chains of cube-like silver clusters connected with L1 and tBuCC- ligands. In compound 2, the Ag10 clusters surrounded by six tBuCC- ligands are linked by silver atoms to 1D chains, which are further extended by L2 ligands to a rare 3D framework. From the topological view, the structure of 2 can be regarded as α-Po topology. The luminescence properties indicated that the two complexes display more than one peak maxima at 298 K using 335 nm excitation.

Syntheses and crystal structures of Ni(II) complexes with pyridine-based macrocyclic ligands

Three pyridine-based macrocyclic ligands, two containing one pyridine pendant arm (L1 and L2) and one containing piperazine rings in the macrocyclic scaffold (L3), with an increasing size of the macrocycle from 12-, 14- to 30-membered ring for L1–L3 were synthesized and characterized. A series of Ni(II) complexes with all these ligands, with molecular formulas [NiL1(CH3OH)](ClO4)2 (1), [NiL2(CH3CN)](ClO4)2 (2), and [Ni2L3(DMF)2(CH3CN)2](ClO4)4 (3) (DMF = N,N–dimethylformamide), was prepared and thoroughly characterized. Single crystal X-ray structural analysis confirmed that all the complexes have a coordination number of six and their geometries are close to octahedral. In the case of the mononuclear complexes 1 and 2, all the nitrogen atoms of the macrocycle are coordinated, however, in the dinuclear complex 3 with the piperazine-based ligand L3, two nitrogen donor atoms (of the total number of ten) are uncoordinated. The first coordination spheres of all the complexes are completed by solvent molecules. The values of effective magnetic moments, determined by the Evans method in solution, are 3.12, 3.19 and 4.36 µB for complexes 1, 2 and 3, respectively, which correspond well to the theoretical spin-only values.

Palladium complex of sulphated schiff base with ortho-vanillin as catalyst for O-arylation of phenol

Organochalcogen compounds due to their hassle-free synthesis and air and moisture insensitive nature have attracted substantial attention in scientific world. They have profound applications in the development of catalytic systems that have emerged as efficient catalysts in various chemical transformations. Organochalcogen ligands have contributed to the backbone of several catalytic systems used for O-arylation reaction which is an effective tool for the synthesis of diaryl ether substituents. Synthesis of several bioactive compounds rely on this method. A thioether ligand L1 has been prepared by reaction of 3-(chloropropyl)amine hydrochloride with the insitu generated PhSNa. The L1 has been condensed with o-vanillin to synthesize ligand L2 having imine functionality. The structure of ligand L2 has been authenticated using proton and carbon-13 NMR techniques. The synthesis of an efficient N, S coordinated bidentate novel palladium complex 1 ([Pd(L2)Cl2]), by the reaction of ligand L2 with [PdCl2(CH3CN)2] in chloroform-hexane system has been carried out. The structure of 1 has also been corroborated by 1H ,13C{1H} NMR and mass spectroscopic techniques. Its catalytic potential has been tested for etherication of various aryl bromides with phenol. Cheaply available aryl chlorides have also been coupled to determine the efficiency of Pd(II) complex 1. The complex 1 gave good yields while exhibiting excellent tolerance towards electronically diverse aryl halides with 0.5 mol% catalyst loading. The nature of catalysis has been found to be purely homogeneous on conducting mercury and triphenylphosphine poisoning tests.

Study of versatile coordination modes, antibacterial and radical scavenging activities of arene ruthenium, rhodium and iridium complexes containing fluorenone based thiosemicarbazones

Halide-bridged metal precursors [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru, Rh and Ir) on reaction with thiosemicarbazone derivative ligands (L1, L2 and L3) yielded a series of mononuclear ruthenium, rhodium and iridium complexes and their corresponding dinuclear analogues. All these complexes (1-9) were characterized by analytical and spectroscopic techniques. Single-crystal X-ray diffraction studies determined the molecular structures of complexes 1, 5, 7-9. The compounds were screened for their in vitro antibacterial activity against gram-positive Staphylococcus aureus (MTCC 3160, MMSA, ESKAPE) and Bacillus thuringiensis (MTCC 8995) and gram-negative Escherichia coli (MTCC 1687) and Pseudomonas aeruginosa (MTCC 1688, ESKAPE) strains, where they exhibit the significant antibacterial effect. In addition, the compounds were also investigated for antioxidant activities using DPPH radical scavenging assays, in which most of them displayed substantial antioxidant activities. Furthermore, the binding of ligand L3 with biomolecules such as Salmon milt DNA (SM-DNA) investigated by UV-Vis absorption spectroscopy revealed an intercalative mode of interaction.

In situ acetonitrile/water mixed solvents: An ecofriendly synthesis and structure Explanations of Cu(II), Co(II), and Ni(II) complexes of thioxoimidazolidine

ABSTRACT. The bidentate oxoacetate derivative of 4-oxo-2-thiazolidine 4ligand (L1) synthesized by the reaction of 1-(1-(Pyridin-3-yl)ethylideneamino)-2-thioxoimidazolidin-4-one 3 with diethyl oxalate with both traditional and microwave irradiation methods. The metal ion complexes of mixed ligands L1 and L2 (acetonitrile) were prepared by condensation a solution mixture of Co(II) Ni(II), and Cu(ІІ) metal chloride salts with the ligands (L1 and L2) in distilled water with stirring. The complexes were characterized by the micro analysis (C, H, N), chloride content, FT-IR, UV-Vis spectra, thermal gravimetric analysis (TGA), molar conductivity as well as magnetic susceptibility measurement. According to the obtained data the suggested coordination geometries of these complexes were suggested as octahedral structure. All the synthesized complexes were found to be electrolyte due to the presence of chloride ions outside the coordination sphere. The antibacterial activity of the L1 ligand and their metal ion complexes have been studied by screening against various microorganisms, G+ bacteria (Bacillus subtillis, Streptococcus pneumonia, and Staphyloccoccus aurease), G-bacteria (E. coli, and Pesudomonas Sp.) and fungi (Aspergillus nigaer, and Penicillium Sp.). The metal ion complexes gave the formulae: [M(L1)(L2)2(H2O)2]Cl2where M = Co(II) Ni(II), and Cu(ІІ).
 
 KEY WORDS: Imidazolidine, Microwave irradiation, Transition metals complexes, Biological activity
 
 Bull. Chem. Soc. Ethiop. 2021, 35(2), 351-364.
 DOI: https://dx.doi.org/10.4314/bcse.v35i2.10

BODIPY-Ruthenium(II) Bis-Terpyridine Complexes for Cellular Imaging and Type-I/-II Photodynamic Therapy.

A series of multichromophoric ruthenium(II) complexes with the formulation [Ru(tpy-BODIPY)(tpy-R)]Cl2 (1-4), having a heteroleptic Ru(II)-bis-tpy (tpy = 4'-phenyl-2,2':6',2″-terpyridine) moiety covalently linked to a boron-dipyrromethene (BODIPY) pendant, have been prepared and characterized and their application as a phototherapeutic and photodetection agent in cancer therapy has been explored. Ligand L1 with a terpyridine-BODIPY moiety and complex 1 as its PF6 salt (1a) have been structurally characterized by a single-crystal X-ray diffraction study. Complex 1a has a distorted-octahedral RuN6 core with a Ru(II)-bis-terpyridine unit that is covalently linked to one photoactive BODIPY unit. The complexes exhibit strong absorbance near 502 nm (ε ≈ (3.7-7.8) × 104 M-1 cm-1) and high singlet oxygen sensitization ability, giving singlet oxygen quantum yield (ΦΔ) values ranging from 0.57 to 0.75 in DMSO. An emission-based study using complex 4 and Singlet Oxygen Sensor Green (SOSG) displays the formation of singlet oxygen inside the cells and also in the buffer medium upon light irradiation. DNA (pUC19) photocleavage experiments using ROS scavengers/stabilizers reveal photoinduced generation of singlet oxygen by a type-II process and of the superoxide anion radical by a type-I process. Complex 4 having a pendant biotin moiety as a cancer cell targeting group shows high photocytotoxicity with a remarkable phototherapeutic index (PI) value of >1400 in HeLa cancer cells with a low light dose activation (400-700 nm, 2.2 J cm-2). The complexes display reduced activity in noncancerous HPL1D cells. The emission property of the complexes is used for cellular imaging, thus making them suitable as next-generation theranostic PDT agents.

Band gap engineering of amine functionalized Ag(I)-based coordination polymers and their plasmonic Ag0 coupled novel visible light driven photo-redox system for selective oxidation of benzyl alcohol

We developed a one-pot synthetic route to design Ag nanoparticles (NPs) coupled mixed ligand Ag(I) coordination polymer (CP), Ag@Ag(I)-CP (40% NH2) for photocatalysis. Initial combined (experimental and DFT) study on mixed ligand CPs demonstrates that a rational substitution of ligand L1: 1,4-benzenedicarboxylate by L2: 2 amino 1,4-benzenedicarboxylate enhances porosity and reduction of energy gap (2.9 eV) due to highest occupied crystal orbital (HOCO; + 2.4 V vs. NHE) suitable for BA oxidation selectively to benzaldehyde (BD) ((E0BA/BD = + 1.9 V). When Ag NP (~ 6–7 nm) is in-situ encapsulated on CP, formed a coupled structure Ag@Ag(I)-CP (40% NH 2), which offered advantages on BA oxidation (k (O2) = 7.4 × 10-4 min-1; yield: 19.1% BD, and k (persulfate) = 38.7 × 10-4 min-1; yield: 54.1% BD) along with significant stability, reusability and competitiveness than other Ag or precious metal NPs. The new material offers numerous possibilities for applications in oxidative organic transformations reactions. The simple synthetic strategy demonstrated in this work for the coupling of Ag(I) based coordination polymers with metal nanoparticles at the molecular scale for semiconductor like applications under visible light will accelerate extensive research in near future.

Synthesis and Near-Infrared Photothermal Conversion of Discrete Supramolecular Topologies Featuring Half-Sandwich [Cp*Rh] Units.

Although a large number of novel supramolecular topologies featuring half-sandwich [Cp*Rh] units have been reported, investigations into the properties of these architectures are astoundingly rare. In addition, the bidentate ligands employed to prepare these species have remained relatively homogeneous (i.e., symmetrical bis(pyri-4-dyl) ligands). To address these paucities in the field, the novel unsymmetrical ligand L2 and the rarely reported pyri-3-dyl ligand L3, all bearing aromatic phenazine groups (an N-heterocyclic analog of anthracene), were synthesized in addition to the common symmetrical pyri-4-dyl L1. [3]Catenane, [2]catenane, and Borromean rings assemblies were constructed successfully by the self-assembly of L1 with different building blocks. Afterward, ligand L2 was applied to prepare two novel molecular-tweezer-like compounds. Lastly, a twisted [2]catenane (relative to the [2]catenane constructed using L1) and a sandwiched metallarectangle were obtained using L3. π-π stacking interactions were observed to play a significant role in stabilizing these topologies, which also promoted nonradiative migration and triggered photothermal conversion in both the solution and the solid state. In the solution state, a clear rule of thumb was derived whereby the NIR photothermal conversion efficiency increased as the π-π stacking increased, and a very high photothermal conversion efficiency (35.5-62.4%) was observed. In addition, this family of half-sandwich-based assemblies also exhibited good photothermal conversion properties in the crystalline and noncrystal powder states. This research provides a novel method to synthesize excellent NIR photothermal conversion materials featuring half-sandwich [Cp*Rh] units and points to potential applications in the near future.

Novel palladium (II) complexes with iminocoumarin ligands: Synthesis, characterisation, electrochemical behaviour, DFT calculations and biological activities, ADMET study and molecular docking

New Palladium (II) complexes with a series of iminocoumarin derivatives have been synthesized and characterized by analytical analysis, spectral methods, magnetic measurements and thermal studies. The experimental results indicated that the Pd(II) complexes are coordinated to the bidentate iminocoumarin derivatives with a distorted square planar geometry. The DFT calculations were performed in order to optimize the geometric structures, to calculate structural parameters and to explain the chemical reactivity of the synthesized compounds. Electrochemical behaviour of the synthesized compounds was studied by cyclic voltammetry. The antioxidant activity of free ligands and their Pd(II) complexes have been evaluated using the DPPH method. The antimicrobial activity was also evaluated in Vitro against two Gram-negative (E. coli, Klebsiella pneumonia), two gram-positive (Staphylococcus aureus, Enterococcus faecalis) and three fungal strains (Candida albicans, Candida tropicalis and Aspergillus niger) using the agar-diffusion method. The ADMET study was also accomplished in order to predict pharmacokinetic and toxicity of the synthesized compounds. Finaly, and in order to study the molecular interaction of the ligand L3 and its corresponding Pd(II) complex with the microbial enzymes; Docking studies were employed.

Thermodynamic Study of Oxidovanadium(IV) with Kojic Acid Derivatives: A Multi-Technique Approach.

The good chelating properties of hydroxypyrone (HPO) derivatives towards oxidovanadium(IV) cation, VIVO2+, constitute the precondition for the development of new insulin-mimetic and anticancer compounds. In the present work, we examined the VIVO2+ complex formation equilibria of two kojic acid (KA) derivatives, L4 and L9, structurally constituted by two kojic acid units linked in position 6 through methylene diamine and diethyl-ethylenediamine, respectively. These chemical systems have been characterized in solution by the combined use of various complementary techniques, as UV-vis spectrophotometry, potentiometry, NMR and EPR spectroscopy, ESI-MS spectrometry, and DFT calculations. The thermodynamic approach allowed proposing a chemical coordination model and the calculation of the complex formation constants. Both ligands L4 and L9 form 1:1 binuclear complexes at acidic and physiological pHs, with various protonation degrees in which two KA units coordinate each VIVO2+ ion. The joined use of different techniques allowed reaching a coherent vision of the complexation models of the two ligands toward oxidovanadium(IV) ion in aqueous solution. The high stability of the formed species and the binuclear structure may favor their biological action, and represent a good starting point toward the design of new pharmacologically active vanadium species.

Tuning Excited-State Properties of [2.2]Paracyclophane-Based Antennas to Ensure Efficient Sensitization of Lanthanide Ions or Singlet Oxygen Generation

The multistep synthesis of original antennas incorporating substituted [2.2]paracyclophane (pCp) moieties in the π-conjugated skeleton is described. These antennas, functionalized with an electron donor alkoxy fragment (A1) or with a fused coumarin derivative (A2), are incorporated in a triazacyclonane macrocyclic ligand L1 or L2, respectively, for the design of Eu(III), Yb(III), and Gd(III) complexes. A combined photophysical/theoretical study reveals that A1 presents a charge transfer character via through-space paracyclophane conjugation, whereas A2 presents only local excited states centered on the coumarin-paracyclophane moiety, strongly favoring triplet state population via intersystem crossing. The resulting complexes EuL1 and YbL2 are fully emissive in red and near-infrared, respectively, whereas the GdL2 complex acts as a photosensitizer for the generation of singlet oxygen.

Theoretical Insights into the Separation of Am(III)/Eu(III) by Hydrophilic Sulfonated Ligands

In this work, we focused on the separation of Am(III)/Eu(III) with four hydrophilic sulfonated ligands (L) based on the framework of phenanthroline and bipyridine through scalar relativistic density functional theory. We studied the electronic structures of [ML(NO3)3] (M = Am, Eu) complexes and the bonding nature between metal and ligands as well as evaluated the separation selectivity of Am(III)/Eu(III). The tetrasulfonated ligand L2 with a bipyridine framework has the strongest complexing ability for metal ions probably because of the better solubility and flexible skeleton. The disulfonated ligand L1 has the highest Am(III)/Eu(III) selectivity, which is attributed to the covalent difference between the Am-N and Eu-N bonds based on the quantum theory of atoms in the molecule analysis. Thermodynamic analysis shows that the four hydrophilic sulfonated ligands are more selective toward Am(III) over Eu(III). In addition, these hydrophilic sulfonated ligands show better complexing ability and Am(III)/Eu(III) selectivity compared to the corresponding hydrophobic nonsulfonated ones. This work provides theoretical support for the separation of Am(III)/Eu(III) using hydrophilic sulfonated ligands.

A Tetraarylpyrrole‐Based Phosphine Ligand for the Palladium‐Catalyzed Amination of Aryl Chlorides

AbstractA tetraarylpyrrole‐based phosphine ligand L1 in combination with Pd(dba)2 provided a catalyst for the Buchwald‐Hartwig amination reaction. A variety of amines were rapidly coupled with aryl chlorides at a Pd loading of 0.5 mol%. The selective monoarylation of aliphatic primary amines was achieved in the presence of 0.8 equiv. water. Comparison experiments were also conducted, which revealed that the catalytic activity of L1 is superior to representative phosphine ligands in the Pd‐catalyzed C−N coupling of various amines.magnified image

Mesoionic Carbenes in Low- to High-Valent Vanadium Chemistry.

We report the synthesis of vanadium(V) oxo complex 1 with a pincer-type dianionic mesoionic carbene (MIC) ligand L1 and the general formula [VOCl(L1)]. A comparison of the structural (SC-XRD), electronic (UV–vis), and electrochemical (cyclic voltammetry) properties of 1 with the benzimidazolinylidene congener 2 (general formula [VOCl(L2)]) shows that the MIC is a stronger donor also for early transition metals with low d-electron population. Since electrochemical studies revealed both complexes to be reversibly reduced, the stronger donor character of MICs was not only demonstrated for the vanadium(V) but also for the vanadium(IV) oxidation state by isolating the reduced vanadium(IV) complexes [Co(Cp*)2][1] and [Co(Cp*)2][2] ([Co(Cp*)2] = decamethylcobaltocenium). The electronic structures of the compounds were investigated by computational methods. Complex 1 was found to be a moderate precursor for salt metathesis reactions, showing selective reactivity toward phenolates or secondary amides, but not toward primary amides and phosphides, thiophenols, or aryls/alkyls donors. Deoxygenation with electron-rich phosphines failed to give the desired vanadium(III) complex. However, treatment of the deprotonated ligand precursor with vanadium(III) trichloride resulted in the clean formation of the corresponding MIC vanadium(III) complex 6, which undergoes a clean two-electron oxidation with organic azides yielding the corresponding imido complexes. The reaction with TMS-N3 did not afford a nitrido complex, but instead the imido complex 10. This study reveals that, contrary to popular belief, MICs are capable of supporting early transition-metal complexes in a variety of oxidation states, thus making them promising candidates for the activation of small molecules and redox catalysis.

Synthesis of phenanthroline-based ligand and its UV activable tetracarbonyl photoCORMs based on chromium, molybdenum, and tungsten as cytotoxic and antimicrobial agents

A phenanthroline-based ligand L1 ((((1,10-phenanthrolin-5-yl)imino)methyl)-6-methoxyphenol) was synthesized and reacted with chromium, molybdenum, and tungsten hexacarbonyl to form ultraviolet (UV) activable photoCORMs C1, M1, and T1, respectively. All compounds were characterized via IR, 1H-NMR, 13C-NMR, and CHN elemental analyses, and the X-ray crystal structures of L1 and M1 were determined. The half-life of the photoCORMs decreased with an increasing concentration and the rate of CO release increased in the order of T1 < M1 < C1, with C1 having the shortest half-life (7.4 seconds at 60 µM). Both M1 and T1 displayed remarkable stability in 10% DMSO-PBS solution over 48 hours in the dark, whereas C1 showed signs of decomposition. In the absence of UV, all compounds exhibited appreciable cytotoxicity against human-derived colorectal adenocarcinoma HCT 116, with T1 being the most cytotoxic (IC50 5.49 µM). The cytotoxicity of the photoCORMs were elevated substantially after brief exposure to UV light (365 nm), with that of C1 having the most drastic improvement (IC50 from 9.98 to 1.24 µM). Moreover, all compounds were selective towards HCT 116 while being relatively less toxic against normal human colon fibroblast CCD-18Co. Furthermore, all compounds were generally not active in the bactericidal and growth inhibitory effects against the tested bacteria and fungi when UV light is absent, except for L1 that exhibited notable activity against B. cereus, B. subtilis, E. coli, K. pneumoniae, and S. flexneri (MIC ≤ 12.5 mg/ml). In contrast, the photoCORMs showed significant improvement in the growth inhibitory effect against several microbes in the presence of UV light, viz., B. cereus, B. subtilis, methicillin-sensitive S. aureus (ATCC 29213 and 33591 strain), and S. flexneri, while no notable improvement in the bactericidal effect was shown.

Chromium catalysts based on PNP(NR2)2 ligands for selective ethylene oligomerization

High active and selective 1–3 chromium catalysts based on the corresponding Ph2PN(cyclopentyl)P (NR2)2‐type L1–L3 ligands (L1: R = methyl, L2: R = ethyl, L3: R = isopropyl) have been explored for selective ethylene tri‐/tetramerization. We found that the ligand substituents and the experimental conditions considerably influenced the catalytic performance of 1–3 based catalysts. Combining a higher ethylene pressure can elevate the selectivity of 1‐octene (67.98%) of precatalyst 1 with high catalytic activity (9.3 × 106 g/[molCr h]). Furthermore, precatalysts 2–3 efficiently offer selective ethylene trimerization and afforded 97.76% 1‐hexene selectivity with 5.8 × 106 g/(molCr h) catalytic activity (in case precatalyst 3). A relatively low catalyst mass, high Al/Cr molar ratio, and high ethylene pressure display excellent catalytic activity and selectivity for ethylene oligomerization.