Cationic Complexes Research Articles

Panoply of P: An Array of Rhenium-Phosphorus Complexes Generated from a Transition Metal Anion.

We expand upon the synthetic utility of anionic rhenium complex Na[(BDI)ReCp] (1, BDI = N,N'-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate) to generate several rhenium-phosphorus complexes. Complex 1 reacts in a metathetical manner with chlorophosphines Ph2PCl, MeNHP-Cl, and OHP-Cl to generate XL-type phosphido complexes 2, 3, and 4, respectively (MeNHP-Cl = 2-chloro-1,3-dimethyl-1,3,2-diazaphospholidine; OHP-Cl = 2-chloro-1,3,2-dioxaphospholane). Crystallographic and computational investigations of phosphido triad 2, 3, and 4 reveal that increasing the electronegativity of the phosphorus substituent (C < N < O) results in a shortening and strengthening of the rhenium-phosphorus bond. Complex 1 reacts with iminophosphane Mes*NPCl (Mes* = 2,4,6-tritert-butylphenyl) to generate linear iminophosphanyl complex 5. In the presence of a suitable halide abstraction reagent, 1 reacts with the dichlorophosphine iPr2NPCl2 to afford cationic phosphinidene complex 6+. Complex 6+ may be reduced by one electron to form 6•, a rare example of a stable, paramagnetic phosphinidene complex. Spectroscopic and structural investigations, as well as computational analyses, are employed to elucidate the influence of the phosphorus substituent on the nature of the rhenium-phosphorus bond in 2 through 6. Furthermore, we examine several common analogies employed to understand metal phosphido, phosphinidene, and iminophosphanyl complexes.

Structural and vibrational spectroscopic analysis of two Au(I) − NHC carbene complexes potential anticancer agents with intramolecular aurophilic interactions: A DFT study

Structural, electronic, and vibrational spectroscopic analysis using DFT/B3LYPD with LanL2DZ and SDD basis of two novel cationic gold(I) complexes with potential anticancer application exhibiting intramolecular aurophilic Au···H–N interactions, ranging from 2.74 to 2.84 Å. Both basis sets yielded equilibrium geometries and computed IR spectra in excellent agreement with X-ray structures and experimental IR spectra data. Despite structural differences in the thione co-ligand, both cationic complexes have remarkably similar dipole moments ranging from 6.4 to 6.6 D and HOMO-LUMO energy gaps, ranging from 5.0 to 5.3 eV, indicating that both possess almost identical solubility and similar chemical stability. Solvation free energies ranging from −35.9 to −39.0 kcal/mol were calculated using the implicit solvation SMD model, suggesting solvent effects play a significant role.

Study of antibacterial effects of Transcarpathian clinoptilolite compositions modified in different chemical ways

Background. Natural clinoptilolite (CL) meets most of the requirements for the multifunctional mineral nanomaterials. It is considered biologically neutral and non-toxic. CL is the only representative of natural zeolites that has been approved for use in medical practice and food industry. Antibacterial activity of Transcarpathian clinoptilolite was shown to be enhanced via its modification using thermal, chemical and mechanochemical treatments. The natural form of this mineral contains a significant concentration of surface silanol (-OH) groups. An increase in the efficiency of zeolite-based materials in terms of biological activity can be achieved by means of thermal and chemical treatments, replacement of cations in the exchange complex, doping with heavy metal cations, or mechanochemical treatment. Materials and Methods. FTIR spectroscopy, Electronic spectroscopy, Particle size distribution, IR spectroscopy, Crystal structure and morphology, Measurement of antibacterial activity. Results. Intact and thermally modified CL was shown to exhibit weak antibacterial effect, while its mechanical modification led to an enhanced activity. It was established that H-form of clinoptilolite demonstrated higher efficiency in inhibiting the growth of Gram-positive bacteria, compared to the Na-form of the clinoptilolite, but their effect on growth of Gram-negative bacteria was insignificant. Such an activity was accompanied by an increase in the specific surface area and porosity that promoted better contact with bacteria. Conclusions: Different samples of CL had dissimilar effect on specific types of bacteria. Intact CL has a weak antibacterial activity of inhibiting growth of microorganisms, while thermal, chemical, and mechanical modifications of the CL structure differentially increased such an activity. The H-form of CL inhibited the growth of Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis) more effectively compared to the Na-form of CL. However, H-form of CL has a weak effect on growth of the Gram-negative bacteria (Pseudomonas aeruginosa, Pseudomonas fluorescens).

Salt Solutions of Molecular Containers of Cucurbiturils: Relationship Between the Characteristics of Cationic Complexes and Adsorbate Layers with Their Participation

Salt Solutions of Molecular Containers of Cucurbiturils: Relationship Between the Characteristics of Cationic Complexes and Adsorbate Layers with Their Participation

Synthetic and Structural Peculiarities of Neutral and Cationic Molybdenum Imido and Tungsten Oxo Alkylidene Complexes Bearing Weakly Coordinating N‐Heterocyclic Carbenes

AbstractThe syntheses of the neutral molybdenum imido alkylidene N‐heterocyclic carbene (NHC) complexes of the general formula [Mo(NAr)(CHCMe2Ph)(NHC)XY] (Ar=2‐tBu‐C6H4, 2‐CF3‐C6H4, 2,6‐Me2‐C6H3, 2,6‐Cl2‐C6H3, adamantyl; X, Y=OTf, OC(CF3)3, OCH(CF3)2, OC6F5, SC6F5, 2,5‐bis(pentafluorophenyl)phen‐1‐yl) bearing electron‐withdrawing NHCs (1,3‐dimethyl‐4,5‐dichloroimidazol‐2‐ylidene (IMeCl2), 1,3,4‐triphenyl‐1,2,4‐triazol‐5‐ylidene (TPT)) are reported. Complementary, the corresponding cationic molybdenum imido alkylidene NHC complexes of the general formula [Mo(NAr)(CHCMe2R)(NHC)X+][B(ArF)4−/Al(OC(CF3)3)4−] (R=Me, Ph; B(ArF)4−=tetrakis (3,5‐bis(trifluoromethyl)phenyl)borate) have been prepared. Aiming at tungsten oxo complexes, reaction of [W(O)Cl2(CHCMe2Ph)(PMe2Ph)2] with [1,3‐dimethyl‐4,5‐dichloroimidazol‐2‐ylidene⋅AgI] (IMeCl2⋅AgI) followed by the addition of lithium terphenoxide yields [W(O)(CHCMe2Ph)(IMeCl2)(DPPO)2]. For comparison, [W(O)Cl(CHCMe2Ph)(IMes)(OSi(OtBu)3)] was prepared via reaction of [W(O)Cl2(CHCMe2Ph)(PMe2Ph)(IMes)] with KOSi(OtBu)3. [W(O)(CHCMe2Ph)(IMeCl2)(DPPO)(Et2O)+][B(ArF)4−] (DPPO=2,6‐diphenylphenoxide) became accessible via reaction of [W(O)(DPPO)2(CHCMe2Ph)(IMeCl2)] with anilinium B(ArF)4−. The structural peculiarities of selected complexes are reported. Benchmark ring‐closing metathesis and homometathesis reactions revealed that the neutral complexes bearing weakly coordinating NHCs such as IMeCl2 and TPT possessed only moderate activity, which could, however, be improved by preparing the corresponding cationic metal alkylidene complexes.

Trianionic Carbocyclic NCN Pincer Ligand: Coordination Chemistry and Reactivity Studies.

(BCHT-NCN)H3 (1) [1,6-bis(methylene(bis-2,6-diisopropylaniline)(benzo)cycloheptatriene)] was synthesized by nucleophilic substitution treating 1,6-bis(methylenebromide)(benzo)cycloheptatriene with 2 equiv of Li[2,6-iPr2C6H3NH], Li[Dipp-NH]. Triple deprotonation of (BCHT-NCN)H3 (1) using n-BuLi yields the deprotonation product [(BCHT-NCN)Li3] (2), which crystallizes as a dimer [{[BCHT-NCN]Li3(Et2O)2}2] (2)2. Coordination compounds of the trianionic pincer ligand were obtained with SnCl2, YCl3(THF)3.5, and HfCl4(THF)2: [(BCHT-NCN)SnLi] (3), [(BCHT-NCN)Y(THF)2] (4), [(BCHT-NCN)HfCl2][Li(THF)4] (5), respectively. A hafnium hydride complex [(BCHT-NCN)HfH(HBEt3)][K(Et2O)2] (6) was isolated after reaction of 5 with K[HBEt3]. A MeNHC substitution product [(BCHT-NCN)HfCl(MeNHC)] (7) was synthesized treating compound 5 with MeNHC at rt. Following an n-BuLi reaction of 7 gives an alkyl complex [(BCHT-NCN)Hf(n-Bu)(MeNHC)] (8). Thermolysis of 7 yields the isomerization product [(BCHT-NCN#)HfCl(MeNHC)] (9), which was transferred into a methyl complex [(BCHT-NCN#)HfMe(MeNHC)] (10) upon treatment with MeMgBr. Hydride abstraction from complex 9 leads to a cationic complex [(BCHT-NCN+)HfCl(MeNHC)][Al(OtBuF)4] (11).

Chemistry of ruthenium complexes with hexamethylbenzene and butadienesulfonyl ligands: Synthesis and reactivity toward phosphites and silver triflate

The addition reaction of (η6-C6Me6)Ru(Cl)(1-2,5-η-CH2CHCHCHSO2) (1) with one equivalent of P(OMe)3 or P(OPh)3 led to the formation of the corresponding compounds (η6-C6Me6)Ru(Cl)(5-η-SO2CHCHCHCH2)(P(OR)3) (R = Me, 4a; Ph, 4b). After 4a and 4b lose AgCl in presence of AgOTf, the immediate coordination of the terminal double bond of the butadienesulfonyl ligand affords the corresponding cationic complexes [(η6-C6Me6)Ru(1-2,5-η-CH2CHCHCHSO2)(P(OR)3]OTf (R = Me, 5a; Ph, 5b). The alternative metathesis reaction between dichlorido compounds (η6-C6Me6)Ru(Cl)2(P(OR)3) (R = Me, 2a, Ph, 2b) and the potassium butadiene sulfinate K(SO2CHCHCHCH2) (3) was only successful in the case of 4a. The 1H, 13C{1H} NMR data of 4a and 4b are consistent with a butadienesulfonyl ligand coordinated preferentially as an S conformer, while only traces of the thermodynamic W conformer have been seen in solution for 4a. The single crystal analysis of neutral 4a and cationic 5b reveals the presence of the butadienesulfonyl ligand binding to ruthenium exclusively through the sulfur atom in the case of 4a, while in 5b, the coordination of the terminal double bond to the metal center also occurs. A comparative study of the influence of the phosphite and phosphine ligands on analogue isoelectronic molecular structures with the η6-C6Me6 and η5-C5Me5 anchored ligands is analyzed. The high stability of 2a and 2b is corroborated and compared to the phosphine analogues. The single crystal of 2b is also discussed.

Electrocatalytic facets of a newly designed cobalt(III) complex towards sustainable hydrogen evolution

A hybrid cobalt complex (C7H10ON)[Co(L)2].CH3OH (Co-complex) bearing an organic cation and anionic cobalt complex has been designed, synthesized, and structurally characterized. The tridentate chelator, 2-((2-hydroxybenzylidene)amino)-4-methylphenol (H2L), was prepared by the condensation reaction between salicylaldehyde and 4-methyl-2-amino phenol. Crystal structure analysis reveals a slight distortion in the octahedral coordination geometry of the cobalt(III) centre. This complex was evaluated in the hydrogen evolution reaction (HER) using a glassy carbon working electrode in acetonitrile (ACN), using tBu4NClO4 as the supporting electrolyte. The catalyst exhibited heightened catalytic activity when acetic acid was introduced, leading to a significant elevation in the catalytic wave at −1.6 V (V vs. Ag wire). The most pronounced activity was observed by adding 15 mM acetic acid, with a turnover number (TON) of 10.1. The catalyst’s durability was confirmed through controlled potential electrolysis (CPE) at −1.6 V for 2 h, displaying a steady current for the initial 20 min, followed by a gradual increase over the subsequent 2 h. A negligible amount of deposited metallic cobalt on the surface of the glassy carbon electrode through a ligand dissociation was evident during the electrocatalytic studies, as ensured by X-ray Photoelectron Spectroscopy (XPS) analysis. Further, the presence of ligand-centric reduction wave in the complex signifies the synergistic effect of the M−L cooperation and offers a plausible ECEC mechanistic route for the release of molecular hydrogen.

Hydrogenolysis of Cationic Half-Sandwich Zinc Complexes Containing a Chelating Amine: Facile Cleavage of Zinc-Carbon Bond by Dihydrogen to Give Zinc Hydride Cations.

Cationic half-sandwich zinc complexes containing chelating amines [Cp*Zn(Ln)][BAr4 F] (2 a, Cp*=η3-C5Me5, Ln=N,N,N',N'-tetramethylethylenediamine, TMEDA; 2 b, Ln=N,N,N',N'-tetraethylethylenediamine, TEEDA; 2 c, Cp*=η1-C5Me5, Ln=N,N,N',N'',N''-pentamethyldiethylenetriamine, PMDTA; Ar4 F=(3,5-(CF3)2C6H3)4) reacted with dihydrogen (ca. 2 bar) in THF at 80 °C to give molecular zinc hydride cations [(Ln)ZnH(thf)m][BAr4 F] (3 a,b, m=1; 3 c, m=0) previously reported along with Cp*H. Pseudo first-order kinetics with respect to the concentration of 2 b suggests heterolytic cleavage of dihydrogen by the Zn-Cp* bond, reminiscent of σ-bond metathesis. Hydrogenolysis of the zinc cation 2 b in the presence of benzophenone gave the zinc alkoxide [(TEEDA)Zn(OCHPh2)(thf)][BAr4 F] (5 b). Cation 2 b was shown to catalytically hydrogenate N-benzylideneaniline. The PMDTA complex 2 c underwent C-H bond activation in acetonitrile to give a dinuclear μ-κC,κN-cyanomethyl zinc complex [(PMDTA)Zn(CH2CN)]2[BAr4 F]2 (6 c).

Amine-Terminated Phenanthroline Diimides as Aqueous Masking Agents for Am(III)/Eu(III) Separation: An Alternative Ligand Design Strategy for Water-Soluble Lanthanide/Actinide Chelating Ligands.

Selective actinide coordination (from lanthanides) is critical for both nuclear waste management and sustainable development of nuclear power. Hydrophilic ligands used as masking agents to withhold actinides in the aqueous phase are currently highly pursued, while synthetic accessibility, water solubility, acid resistance, and extraction capability are the remaining problems. Most reported hydrophilic ligands are only effective at low acidity. We recently proved that the phenanthroline diimide skeleton was an efficient building block for the construction of highly efficient acid-resistant hydrophilic lanthanide/actinide separation agents, while the limited water solubility hindered the loading capability of the ligand. Herein, amine was introduced as the terminal solubilizing group onto the phenanthroline diimide backbone, which after protonation in acid showed high water solubility. The positively charged terminal amines enhanced the ligand water solubility to a large extent, which, on the other side, was believed to be detrimental for the coordination and complexation of the metal cations. We showed that by delicately adjusting the alkyl chain spacing, this intuitive disadvantage could be relieved and superior extraction performances could be achieved. This work holds significance for both hydrophilic lanthanide/actinide separation ligand design and, concurrently, offers insights into the development of water-soluble lanthanide/actinide complexes for biomedical and bioimaging applications.

Antifungal and antibacterial activity of two new Ni(II) complexes of a pyrazole-appended thiophene containing bidentate schiff-base ligand: Synthesis, spectroscopy and crystal structures

A new pyrazole-appended thiophene containing Schiff-base ligand, N-(thiophene-2-ylmethyl)-1-(5-methyl-1H-pyrazol-3-yl)methanimine, (MPATA) (1) and its two new di- and mononuclear Ni(II) complexes, [Ni2(MPATA)4 (µ-Cl)2]Cl2 (2) and [Ni(MPATA)3](ClO4)2 (3), respectively, are reported. All the synthesized compounds have been thoroughly characterized by several physico-chemical and spectroscopic studies. Single crystal X-ray diffraction studies have identified 2 as a chloro‑bridged di-nuclear cationic complex, while 3 as a mononuclear distorted octahedral one. In 2, coordination to each metal centre has been occurred by two molecules of ‘NN’ bidentate MPATA and each Ni(II) centre assumes a distorted octahedral geometry. On the other hand, in 3, three molecules of the ‘NN’ bidentate MPATA coordinate to the Ni(II) centre. Both the complexes 2 and 3 exhibit significant hydrogen bonding and intramolecular π···π stacking interactions. All the three compounds have been found to display significant antifungal activity against plant pathogen funguses Colletotrichum siamense (CS) and Fusarium equisetum (F.E) and antibacterial activity against gram-positive and gram-negative bacteria, but no such effects have been found against human pathogen fungus Candida albicans sc5314.

Synthesis, characterization, and biological activity of cationic ruthenium-arene complexes with sulfur ligands.

Five cationic ruthenium-arene complexes with the generic formula [Ru(SAc)(S2C·NHC)(p-cymene)](PF6) (5a-e) were prepared in almost quantitative yields using a straightforward one-pot, two-step experimental procedure starting from [RuCl2(p-cymene)]2, an imidazol(in)ium-2-dithiocarboxylate (NHC·CS2) zwitterion, KSAc, and KPF6. These half-sandwich compounds were fully characterized by various analytical techniques and the molecular structures of two of them were solved by X-ray diffraction analysis, which revealed the existence of an intramolecular chalcogen bond between the oxygen atom of the thioacetate ligand and a proximal sulfur atom of the dithiocarboxylate unit. DFT calculations showed that the C=S…O charge transfer amounted to 2.4kcalmol-1. The dissolution of [Ru(SAc)(S2C·IMes)(p-cymene)](PF6) (5a) in moist DMSO-d6 at room temperature did not cause the dissociation of its sulfur ligands. Instead, p-cymene was slowly released to afford the 12-electron [Ru(SAc)(S2C·IMes)]+ cation that could be detected by mass spectrometry. Monitoring the solvolysis process by 1H NMR spectroscopy showed that more than 22days were needed to fully decompose the starting ruthenium-arene complex. Compounds 5a-e exhibited a high antiproliferative activity against human glioma Hs683 and human lung carcinoma A549 cancer cells. In particular, the IMes derivative (5a) was the most potent compound of the series, achieving toxicities similar to those displayed by marketed platinum drugs.

Reaction of Tl+ with corannulene: Experimental and theoretical study

The interaction of Tl+ cation with corannulene was investigated by using electrospray ionization mass spectrometry (ESI-MS). It was found that the thallium cation Tl+ forms with corannulene (C20H10) two cationic complexes [Tl(C20H10)]+ and [Tl(C20H10)2]+. Quantum chemical calculations proceed by density functional theory with two different functionals (B3LYP and M06-D3) provided the most probable structures of these complexes. In the energetically most favored conformation of [Tl(C20H10)]+ complex, the Tl+ cation lies on the apex of pyramid which base is formed by the central pentagon of the convexly oriented corannulene molecule. In the [Tl(C20H10)2]+ complex the “central” cation Tl+ is situated between two molecules of the corannulene ligand. Both ligand molecules are convex to the Tl+ cation. The interaction energies, E(int), of the considered cation-π complexes [Tl(C20H10)]+ and [Tl(C20H10)2]+ were calculated to be −121.75 and −176.98 kJ/mol, respectively.

Synthesis of cationic lanthanoid tetraphenylborate crown ether complexes

The efficacy of Me3NHBPh4 as a protolytic agent in the generation of reactive lanthanoid cations has been further explored. Reaction of [Nd(BH4)3(thf)4] with Me3NHBPh4 in a 1:3 mole ratio, and dibenzo-18-crown-6 (DB18C6) in thf did not yield [Nd(thf)n][BPh4]3, but [Nd(BH4)2(DB18C6)][BPh4]⋅2THF (1), a complex primed for further functionalisation, was isolated. The structure has an eight coordinate Nd atom with two trans tridentate BH4− ligands. Redox transmetallation/protolysis (RTP) reactions between Yb metal, PhHgC6F5, and Me3NHBPh4 in the presence of 18-crown-6 (18C6) or DB18C6 in MeCN or in thf followed by work up with MeCN yields [Yb(CE)(MeCN)3][BPh4]2⋅nMeCN (CE = 18C6, n = 0 (2), and DB18C6 n = 3 (3)), the structures of which have nine coordinate Yb atoms. Two pairs of MeCN ligands are transoid, whereas the third pair have a small cis NYbN angle. In the absence of a crown ether ligand, the RTP reaction in MeCN yields the known [Yb(MeCN)8] [BPh4]2.

Lithium(I), Cesium(I), Barium(II) and Cadmium (II) [2-(2,6-dichlorophenylamino)phenyl]acetate (diclofenac) complexes and coordination polymers

Two new lithium complexes and three coordination polymers with cesium, barium, and cadmium having deprotonated diclofenac acid (HDFA) ligand are reported. All these non-ionic complexes or the coordination polymers were characterized by single crystal X-ray diffraction, IR and thermal studies. The lithium-diclofenac complexes, [Li(DFA)(H2O)3] and [Li(DFA)(H2O)2(DMF)] were respectively obtained from reaction carried out in aqueous ethanol or dimethylformamide as solvent. Each formed hydrogen bonded 2D-sheets, which were further assembled into 3D-layers by involving edge-on Cl-π interactions. The respective average particle sizes determined by dynamic light scattering of the respective lithium complexes were 648.3 nm and 588.8 nm. The average particle size of the tri-aquated complex dissolved in water was decreased upon addition of dimethylformamide. The cesium coordination polymer [Cs(DFA)(μ-H2O)2]n had two-dimensional sheets formed through dative bonds. The hydrophobic parts of the sheets were projecting outward and two alternative sheets were inter-linked by edge-on chlorine-π interactions (3.391 Å) to provide 3-D supramolecular layered structure. One dimensional barium coordination polymer [Ba(DFA)2(H2O)4]n and a cadmium coordination polymer [{Cd(DMF)4}2+{Cd(DFA)4}2−]n having linear-chain structure were reported. The linear chain of the cadmium coordination polymer was comprised of the coordinatively linked assembly of complex cation [Cd(DMF)4]2+ with anion [Cd(DFA)4]2− located at alternative positions by side-on carboxylate bridges.

Study of the process of tetracycline absorption by soil and its transformation during acid desorption

Introduction. Currently, control over the soil entry of antibiotics used in agriculture is becoming an urgent problem of environmental hygiene. Tetracycline can enter the soil with the excrement of domestic animals and affect biological objects, both microbiological and plant. The chemical form of tetracycline in the soil and the options for its transformation, in particular during sample preparation for analysis, are factors that determine the intensity of this effect and the reliability of analytical control. The lack of information about the transformation of the drug under chemical influence determined the relevance of the research. Materials and methods. The studies were performed using the Stayer chromatographic system with a Shodex IC YS-50 150/4.6 cation column and a Kromasil C18 HPLC column with amperometric and conductometric detection. The objects of research were model soil samples with different tetracycline contents. When conducting research, soddy-podzolic soil from the «Nemchinovka» experimental field (Moscow region) and GSO No. chernozem were used. Results. Solutions obtained after acid-methanol desorption of tetracycline from soil samples were studied using HPLC and IC (Ionochromatographic methods). As a result of desorption, complex forms of substances, including both natural organic substances of the soil and tetracycline components, were established to pass into the aqueous phase. These forms of substances are fixed with a Shodex IC YS-50 cation exchange column and are not fixed by HPLC with a Kromasil C18 column. The possibility of isolating a chromatographic signal corresponding to the tetracycline component using ion chromatography has been demonstrated. Limitations. To create a method for measuring tetracycline in soil, it is necessary to test a larger number of soil species that differ in the content of organic matter to identify in detail the interfering effect of the organic matrix during chromatographic analysis. Conclusion. Research has shown tetracycline chemically to bind to soil matter, forming cationic complexes. After treating the soil with a mixture of concentrated hydrochloric acid and methanol, tetracycline is quantitatively extracted from the soil in combination with natural soil organic matter. These forms of substances are detected by a Shodex IC YS-50 cationic column and are not detected by HPLC with a Kromasil C18 column. Selective analysis of the cationic form containing the tetracycline moiety is possible.

Transition Metal‐Free Catalytic C−H Zincation and Alumination

AbstractC−H metalation is the most efficient method to prepare aryl–zinc and –aluminium complexes that are ubiquitous nucleophiles. Virtually all C−H metalation routes to form Al/Zn organometallics require stoichiometric, strong Brønsted bases with no base‐catalyzed reactions reported. Herein we present a catalytic in amine/ammonium salt (Et3N/[(Et3N)H]+) C−H metalation process to form aryl‐zinc and aryl‐aluminium complexes. Key to this approach is coupling an endergonic C−H metalation step with a sufficiently exergonic dehydrocoupling step between the ammonium salt by‐product of C−H metalation ([(Et3N)H]+) and a Zn−H or Al−Me containing complex. This step, forming H2/MeH, makes the overall cycle exergonic while generating more of the reactive metal electrophile. Mechanistic studies supported by DFT calculations revealed metal‐specific dehydrocoupling pathways, with the divergent reactivity due to the different metal valency (which impacts the accessibility of amine‐free cationic metal complexes) and steric environment. Notably, dehydrocoupling in the zinc system proceeds through a ligand‐mediated pathway involving protonation of the β‐diketiminate Cγ position. Given this process is applicable to two disparate metals (Zn and Al), other main group metals and ligand sets are expected to be amenable to this transition metal‐free, catalytic C−H metalation.

Fluoride Abstraction Induced by Tris(pentafluoroethyl)difluorophosphorane: A Convenient Way to Synthesize Cationic N-Heterocyclic Carbene- and Cyclic (Alkyl)(amino)carbene-Ligated Copper Alkyne and Arene Complexes.

We herein report the convenient synthesis of different N-heterocyclic carbene (NHC)- and cyclic (alkyl)(amino)carbene (cAAC)-ligated copper cations using the weakly coordinating tris(pentafluoroethyl)trifluorophosphate counterion (FAP anion, [(C2F5)3PF3]-). The reaction of the fluorido complexes [(carbene)CuF] (carbene = NHC, cAACMe) 2a-2f and the tris(pentafluoroethyl)difluorophosphorane (C2F5)3PF2 in the presence of alkynes or arenes led to fluoride transfer from Cu to the phosphorane with formation of the cationic transition metal complexes [(carbene)Cu(L)]+ and the weakly coordinating counteranion [(C2F5)3PF3]- (FAP). Using this method, the complexes [(IDipp)Cu(L)]+FAP- (IDipp = 1,3-bis(2,6-di-iso-propylphenyl)-imidazolin-2-ylidene; L = PhC≡CPh, 4d; PhC≡CMe, 5d), [(cAACMe)Cu(L)]+FAP- (cAACMe = 1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene; L = PhC≡CPh, 4f; PhC≡CMe, 5f), [(SIDipp)Cu(C6Me6)]+FAP- (6e), (SIDipp = 1,3-bis(2,6-di-iso-propylphenyl)-imidazolidine-2-ylidene), and [(cAACMe)Cu(C6Me6)]+FAP- (6f) have been synthesized and characterized. The complexes [(IDipp)Cu(C6Me6)]+FAP- (6d) and [(cAACMe)Cu(C6Me6)]+FAP- (6f) have been used as catalysts for the copper(I)-catalyzed cycloaddition of benzyl azide to terminal alkynes.

Transition Metal-Free Catalytic C-H Zincation and Alumination.

C-H metalation is the most efficient method to prepare aryl-zinc and -aluminium complexes that are ubiquitous nucleophiles. Virtually all C-H metalation routes to form Al/Zn organometallics require stoichiometric, strong Brønsted bases with no base-catalyzed reactions reported. Herein we present a catalytic in amine/ammonium salt (Et3N/[(Et3N)H]+) C-H metalation process to form aryl-zinc and aryl-aluminium complexes. Key to this approach is coupling an endergonic C-H metalation step with a sufficiently exergonic dehydrocoupling step between the ammonium salt by-product of C-H metalation ([(Et3N)H]+) and a Zn-H or Al-Me containing complex. This step, forming H2/MeH, makes the overall cycle exergonic while generating more of the reactive metal electrophile. Mechanistic studies supported by DFT calculations revealed metal-specific dehydrocoupling pathways, with the divergent reactivity due to the different metal valency (which impacts the accessibility of amine-free cationic metal complexes) and steric environment. Notably, dehydrocoupling in the zinc system proceeds through a ligand-mediated pathway involving protonation of the β-diketiminate Cγ position. Given this process is applicable to two disparate metals (Zn and Al), other main group metals and ligand sets are expected to be amenable to this transition metal-free, catalytic C-H metalation.

Catalytic promiscuity, cytotoxicity and protein cleavage mediated by mononuclear copper(II) complexes: oxidative and hydrolytic activities

In this work, we describe the synthesis and structural and spectroscopic characterizations of two copper(II) complexes, [(Cu)(L1)(Cl2)].4H2O (1), where L1 is 2-(pyridin-2-yl)-1,3-bis(pyridin-2-ylmethyl)-hexahydropyrimidine, and [Cu(L2)](ClO4)2 (2), where L2 is N1,N1,N3-tris(pyridin-2-ylmethyl)propane-1,3-diamine. The crystalline structure analysis indicates that both complexes are mononuclear and pentacoordinated compounds. In the case of complex 1, it bears a neutral charge, with the ligand coordinating to the Cu(II) center in a tridentate manner, utilizing N-donor atoms. Additionally, two cis-chlorido ligands completing the coordination sphere. On the other hand, complex 2 is a cationic complex, with the ligand coordinated in a pentadentate manner, with only N-donor atoms for coordination around the Cu(II). Complex 1 showed catalytic promiscuity, displaying hydrolytic and oxidative activity. The hydrolytic activity was investigated using bis(2,4-dinitrophenyl) phosphate (2,4-BDNPP) as a phosphodiester substrate and applying the Michaelis–Menten approach, obtaining the following kinetic parameters: kcat = 1.21 × 10-4 s−1; KM = 3.35 × 10-3 molL-1. Complex 1 also accelerates the oxidation of the 3,5-di-tert-butylcatechol (3,5-DTBC) substrate with catalytic efficiency equal to 6.11 L mol-1s-1. Interestingly, we demonstrated that this Cu(II) complex 1 can also cleave the very stable peptide bonds from BSA (bovine serum albumin) through an oxidative mechanism using ascorbate as a reducing agent. Complexes 1 and 2 show good cytotoxic activity against two cancer cell lines: A431 from human squamous cell carcinoma and K562 from chronic myeloid leukemia. This study showed that complexes 1 and 2 are selective towards cancer cells.