Acetonitrile Complex Research Articles

Synthesis and characterisation of dirhodium(II) tetraacetates bearing axial ferrocene ligands

Symmetrical dirhodium(II) tetracarboxylate complexes bearing ferrocene-based supporting ligands in the axial positions, viz. [Rh2(CH3CO2)4L2] (1-3), where L = (diphenylphosphino)ferrocene (1), cyanoferrocene (2), and isocyanoferrocene (3), were prepared from [Rh2(CH3CO2)4] and the respective ferrocene derivative in ethanol. These complexes were structurally characterised by spectroscopic methods, single-crystal X-ray diffraction analysis and cyclic voltammetry. Our results showed that while compounds 1 and 3 are stable in both solid state and solution (complex 1 is very poorly soluble), the nitrile complex 2 easily decomposes through the loss of the isocyanide ligands.

Ligand and solvent effects on the kinetics of the electrochemical reduction of Ni(II) complexes: Experiment and quantum chemical modeling

The two-electron reduction of some Ni(II) complexes with α-diimine ligands ([Ni(bpy)3]2+ and [Ni(pybox)2]2+) at a platinum electrode from acetonitrile (AN) and dimethylformamide (DMF) solutions is investigated by cyclic voltammetry (CV). Digisim simulations are employed to determine kinetic parameters. For [Ni(bpy)3]2+ in AN the first electron transfer (ET) step was found to be rate-controlling. The rate constants of the first and second steps (k1 and k2) are practically the same in the DMF solution. In contrast, the second ET step is rate controlling for the [Ni(pybox)2]2+ complex in AN, while the difference between k1 and k2 for this complex reactant in DMF becomes less noticeable. Molecular modeling based on the quantum mechanical theory of electron transfer and on density functional theory (DFT) calculations is performed for the first time to predict the activation barriers of the two-step heterogeneous redox processes and to elucidate the role of the ligands and solvents in the kinetics of these processes. Three-dimensional reaction free energy surfaces are constructed along the solvent and intramolecular coordinates. The electronic transmission coefficients are estimated as well. The results of model calculations are in qualitative agreement with the experimental data.

Synthesis, Crystal Structures and Properties of Ni(NCS)2‐3‐Cyanopyridine Coordination Compounds including a Ferromagnetic Layered Compound

AbstractReactions of Ni(NCS)2 and 3‐cyanopyridine in different solvents lead to the formation of Ni(NCS)2(3‐cyanopyridine)4 (1) already reported in the literature, Ni(NCS)2(3‐cyanopyridine)2(H2O)2 (2), Ni(NCS)2(3‐cyanopyridine)2(CH3OH)2 (3), Ni(NCS)2(3‐cyanopyridine)2(CH3CN)2 (4) and Ni(NCS)2(3‐cyanopyridine)2 (5). The crystal structures of 1–4 consist of discrete octahedral complexes, in which the thiocyanate anions, as well as the 3‐cyanopyridine coligands, are only terminally N‐bonded. In compound 5 the Ni cations are octahedrally coordinated and linked by pairs of thiocyanate anions into dinuclear units that are further connected into layers by single μ‐1,3‐bridging anionic ligands. TG‐DTA measurements of the discrete complex 1 reveal that in the first step half of the coligands are emitted leading to the formation of compound 5. In contrast, compounds 2 and 3 transform into a new crystalline phase of the same composition (6) upon heating that should also contain μ‐1,3‐bridging anionic ligands, but the outcome of this reaction strongly depends on the reaction conditions. The acetonitrile complex 4 is unstable at room temperature and decomposes into a mixture of different phases including the aqua complex 2. Magnetic measurements of compound 5 prove a ferromagnetic transition at Tc=6.0 K. This result is compared to those obtained for other thiocyanate compounds exhibiting a similar layer topology.

Mapping the Pathway to Organocopper(II) Complexes Relevant to Atom Transfer Radical Polymerization.

The rare organocopper(II) complex [Cu(Me6tren)(CH2CN)]+ (Me6tren = tris(2-(dimethylamino)ethyl)amine) has emerged as an important model of potential byproducts in copper-catalyzed atom transfer radical polymerization. This complex has been generated by controlled potential electrolysis of [Cu(Me6tren)(NCMe)]2+ in the presence of BrCH2CN. Time-resolved UV-vis and continuous wave and pulse electron paramagnetic resonance (EPR) spectra identified [Cu(Me6tren)Br]+ as an intermediate. Hyperfine sublevel correlation and electron nuclear double resonance spectroscopy of samples at different timepoints reveal signals that are assigned to a C-bound cyanomethylate ligand, with distinct 14N and 1H hyperfine coupling constants in comparison with the corresponding N-bound acetonitrile and bromido complexes. The experimental EPR data are supported by density functional theory calculations to understand how the geometries of the species involved produce distinct spectroscopic signatures, and a clear picture of how this unusual organocopper(II) complex is formed has emerged.

Ultrafast Excited-State Dynamics of CuBr3- Complex Studied with Sub-20 fs Resolution.

Ultrafast excited-state dynamics of CuBr3- complex was studied in acetonitrile and dichloromethane solutions using femtosecond transient absorption spectroscopy with 18 fs temporal resolution and quantum-chemical DFT calculations. Upon 640 nm excitation, the CuBr3- complex is promoted to the ligand-to-metal charge transfer (LMCT) state, which then shortly undergoes internal conversion into the vibrationally hot ligand field (LF) excited state with time constants of 30 and 40 fs in acetonitrile and dichloromethane, respectively. The LF state nonradiatively relaxes into the ground state in 2.6 and 7.3 ps in acetonitrile and dichloromethane, respectively. Internal conversion of the LF state is accompanied by vibrational relaxation that occurs on the same time scale. Based on the analysis of coherent oscillations and quantum-chemical calculations, the predominant forms of the CuBr3- complex in acetonitrile and dichloromethane solutions were revealed. In acetonitrile, the CuBr3- complex exists as [CuBr3(CH3CN)2]-, whereas three forms of this complex, [CuBr3CH2Cl2]-, [CuBr3(CH2Cl2)2]-, and [CuBr3(CH2Cl2)3]-, are present in equilibrium in dichloromethane.

Design & Characterization of Pb Electrode for Sensing Trichloroethylene in Ionic Liquid/Acetonitrile Co-Solvents

Design & Characterization of Pb Electrode for Sensing Trichloroethylene in Ionic Liquid/Acetonitrile Co-Solvents

Luminescent heteroleptic copper(I) complexes with polydentate benzotriazolyl-based ligands

Bis(benzotriazol-1-yl)phenylmethane CHPh(btz)2 and tris(benzotriazol-1-yl)methane CH(btz)3 were used as N-donor ligands to prepare luminescent heteroleptic copper(I) complexes. [Cu{CHPh(btz)2}(PPh3)2][BF4] and [Cu{CHPh(btz)2}(DPEphos)][BF4] (DPEphos = bis[(2-diphenylphosphino)phenyl] ether) were obtained from the corresponding borohydride complexes [Cu(BH4)(PPh3)2] and [Cu(BH4)(DPEphos)] and tetrafluoroboric acid. [Cu{CH(btz)3}(PPh3)][BF4] and [Cu{CH(btz)3}(PiPr3)][BF4] were prepared from the acetonitrile complex [Cu(NCCH3)4][BF4]. The complexes exhibited bright yellow or orange emissions upon excitation with near-UV and violet light. The photoluminescent properties were attributed to metal-to-ligand charge transfer transitions on the basis of experimental data and DFT calculations.

Synthesis of a Ru(II) Complex with a Naphthoquinone-Annelated Imidazole Ligand Exhibiting Proton-Responsive Redox and Luminescent Behavior

A mononuclear ruthenium complex, [RuII(L)(bpy)2](PF6), with a naphthoquinone-annelated imidazole ligand HL (2-(pyridin-2-yl)-1H-naphtho[2,3-d]imidazole-4,9-dione) was synthesized and structurally characterized. Electrochemical study reveals that the Ru complex shows four reversible redox waves at +0.98 V, −1.13 V, −1.53 V, and −1.71 V versus SCE in acetonitrile, which are assigned to Ru(II)/Ru(III), L−/L•2−, and two bpy/bpy•− redox couples, respectively. The redox potential of Ru(II)/Ru(III) was positively shifted upon the addition of trifluoromethanesulfonic acid due to protonation of the L− moiety, leading to stabilization of the Ru 4d orbital. In UV-vis absorption measurements for the Ru complex in acetonitrile, a metal-to-ligand charge transfer (MLCT) band was observed at 476 nm, which was shifted to 450 nm by protonation, which might be due to a decrease in the electron delocalization and stabilization of the π orbitals in L−. The blue shift of the MLCT band by protonation was associated with a shift of an emission band from 774 nm to 620 nm, which could be caused by the decreased electronic delocalization in the MLCT excited state. These electrochemical and spectroscopic changes were reversible for the protonation/deprotonation stimuli.

Azavinylidene Complexes from Coupling Reactions of Organonitriles with Phosphines

The reactions of the rhenium(III)-phosphine complex ReCl3(PMePh2)3 with organonitriles (NCR) were studied and found to give novel addition as well as simple substitution products. Refluxing ReCl3(PMePh2)3 in acetonitrile (MeCN) yielded a mixture of the organonitrile rhenium complex ReCl3(PMePh2)2(NCMe) and the rhenium phosphonium-substituted azavinylidene complex ReCl3(PMePh2)2{═N═C(PMePh2)Me}. Similarly, reactions of ReCl3(PMePh2)3 with arylnitriles p-R-C6H4CN (R = H, Me, and Br) gave the corresponding azavinylidene complexes ReCl3(PMePh2)2{═N═C(PMePh2)(p-C6H4R)}. The nitrile complex ReCl3(PPh3)2(NCPh) is unreactive toward external PPh3, but it reacts with excess PMe3 to produce the azavinylidene complex ReCl3(PMe3)2{═N═C(PMe3)Ph}. Computational studies reveal the effect of ligand and substituent of organonitriles on the thermodynamics and kinetics for the reactions of ReCl3(PR3)2(NCR′) with PR3. Both the experimental and computational results indicate that nucleophilic addition of phosphines to coordinated nitriles is more favorable for nitriles with an electron-withdrawing group and for phosphines which are more electron-donating.

Antioxidant, antibacterial and electrochemical activity of (E)-N-(4 (dimethylamino) benzylidene)-4H-1,2,4-triazol-4-amine ligand and its transition metal complexes

Transition metal complexes of Ni(II) (1), Co(II) (2) and Cu(II) (3) supported by a Schiff base ligand, namely (E)-N-(4 (dimethylamino)benzylidene)-4H-1,2,4-triazol-4-amine (L) have been synthesized. The ligand has been characterized by various spectral studies (1H NMR, 13C NMR, FTIR, UV–Vis and ESI-MS). The metal complexes have been characterized by FTIR, UV–Vis, ESI-MS and elemental analysis. . Elemental analysis and ESI-MS studies confirmed that metal complexes form at 1:2 (metal:ligand) ratio. The electrochemical behaviors of the metal complexes in acetonitrile have also been studied using cyclic voltammetry and metal complexes have showed by reducing in their metal center. In vitro stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging assay was used to estimate the antioxidant activity of ligands and its metal complexes. Complex 3 exhibited most potent scavenging property with IC50 value 1.97 ± 0.08 μg/mL among the tested compounds compared to the standard antioxidant ascorbic acid (IC50 value 1.14 ± 0.17 μg/mL). Antibacterial screening investigated by disc diffusion method against gram positive (Staphylococcus aureus, Bacillus subtilis and Staphylococcus epidermidis) and gram negative (Escherichia coli) bacterial strains. The result has exhibited that the complex 2 had prominent inhibitory property against gram positive bacterial strains at the dose of 250 μg/mL and 500 μg/mL. Moreover, the complex 3 have also showed good antibacterial activity against Staphylococcus aureus and Bacillus subtilis at the dose of 500 μg/mL.

Ensemble effects on allylic oxidation within explicit solvation environments.

Umbrella-sampling density functional theory molecular dynamics (DFT-MD) has been employed to study the full catalytic cycle of the allylic oxidation of cyclohexene using a Cu(ii) 7-amino-6-((2-hydroxybenzylidene)amino)quinoxalin-2-ol complex in acetonitrile to create cyclohexenone and H2O as products. After the initial H-atom abstraction step, two different reaction pathways have been identified that are distinguished by the participation of alkyl hydroperoxide (referred to as the "open" cycle) versus the methanol side-product (referred to as the "closed" cycle) within the catalyst recovery process. Importantly, both pathways involve dehydrogenation and re-hydrogenation of the -NH2 group bound to the Cu-site - a feature that is revealed from the ensemble sampling of configurations of the reactive species that are stabilized within the explicit solvent environment of the simulation. Estimation of the energy span from the experimental turnover frequency yields an approximate value of 22.7 kcal mol-1 at 350 K. Whereas the closed cycle value is predicted to be 26.2 kcal mol-1, the open cycle value at 16.5 kcal mol-1. Both pathways are further consistent with the equilibrium between Cu(ii) and Cu(iii) that has previously been observed. In comparison to prior static DFT calculations, the ensemble of both solute and solvent configurations has helped to reveal a breadth of processes that underpin the full catalytic cycle yielding a more comprehensive understanding of the importance of radical reactions and catalysis recovery.

Copper redox mediators with alkoxy groups suppressing recombination for dye-sensitized solar cells

Two copper complexes ([Cu(moby)2]2+/+ (moby=6,6′-bis(methoxymethyl)-2,2′-bipyridine) and [Cu(eoby)2]2+/+, (eoby=6,6′-bis(ethoxymethyl)-2,2′-bipyridine)) with bipyridine ligands were synthesized and used as redox mediators in dye-sensitized solar cells (DSSCs). The DSSCs exhibited high power conversion efficiencies of over 10% under simulated one sun irradiation (100 mW cm−2, AM 1.5G). The introduction of alkoxy groups onto the ligands effectively suppress charge recombination and increased the solubility of the copper complexes in acetonitrile, which led to the high photocurrent and stability of the DSSCs. The redox potentials of [Cu(moby)2]2+/+and [Cu(eoby)2]2+/+ were 0.65 and 0.70 V, respectively, whereas the open-circuit voltages of their DSSCs were still above 1.0 V. The relatively low redox potentials of the copper complexes enable them to match with more sensitizers to realize DSSCs with high photocurrent and photovoltage, providing an opportunity to further improve DSSCs by optimizing the copper redox mediator.

Cationic Group VI Metal Imido Alkylidene N‐Heterocyclic Carbene Nitrile Complexes: Bench‐Stable, Functional‐Group‐Tolerant Olefin Metathesis Catalysts

AbstractDespite their excellent selectivities and activities, Mo‐and W‐based catalysts for olefin metathesis have not gained the same widespread use as Ru‐based systems, mainly due to their inherent air sensitivity. Herein, we describe the synthesis of air‐stable cationic‐at‐metal molybdenum and tungsten imido alkylidene NHC nitrile complexes. They catalyze olefin metathesis reactions of substrates containing functional groups such as (thio‐) esters, (thio‐) ethers and alcohols without the need for prior activation, for example, by a Lewis acid. The presence of a nitrile ligand was found to be essential for their stability towards air, while no decrease in activity and productivity could be observed upon coordination of a nitrile. Variations of the imido and anionic ligand revealed that alkoxide complexes with electron‐withdrawing imido ligands offer the highest reactivities and excellent stability compared to analogous triflate and halide complexes.

Cationic Group VI Metal Imido Alkylidene N-Heterocyclic Carbene Nitrile Complexes: Bench-Stable, Functional-Group-Tolerant Olefin Metathesis Catalysts.

Despite their excellent selectivities and activities, Mo‐and W‐based catalysts for olefin metathesis have not gained the same widespread use as Ru‐based systems, mainly due to their inherent air sensitivity. Herein, we describe the synthesis of air‐stable cationic‐at‐metal molybdenum and tungsten imido alkylidene NHC nitrile complexes. They catalyze olefin metathesis reactions of substrates containing functional groups such as (thio‐) esters, (thio‐) ethers and alcohols without the need for prior activation, for example, by a Lewis acid. The presence of a nitrile ligand was found to be essential for their stability towards air, while no decrease in activity and productivity could be observed upon coordination of a nitrile. Variations of the imido and anionic ligand revealed that alkoxide complexes with electron‐withdrawing imido ligands offer the highest reactivities and excellent stability compared to analogous triflate and halide complexes.

Computational Approaches for Redox Potentials of Iron(IV)‐oxido Complexes

The potential of the redox couple FeIV=O / FeIII–O is of interest for the reactivity of the high‐valent nonheme iron oxidants in enzymes and bioinspired small molecule systems but, unfortunately, experimentally it so far is very poorly described. Discussed are three computational methods that are used in combination with available experimental data derived from titrations of FeIV=O species with ferrocene derivatives in dry acetonitrile, and from spectroelectrochemical titrations of FeIII–OH complexes in wet acetonitrile, i.e. describing the FeIV=O / FeIII–OH couple – both data sets are known to have some ambiguities. First, a DFT‐based method is used to compute the E° values of 14 FeIV=O / FeIII–O couples with an error margin of around 110 mV. A subset of four species of the original data set is used to evaluate a DLPNO‐CCSD(T) based approach, and another subset of complexes, where the spectroelectrochemically determined FeIV=O / FeIII–OH potentials are also known, are used for a Bordwell‐Polanyi analysis, which also yield pKa values. It is shown that the three approaches lead to a consistent picture but due to possible ambiguities with the experimental data, it currently is not possible to fully evaluate the accuracy of the used approaches.

Nitrile group as IR probe to detect the structure and hydrogen-bond properties of piperidinium/pyrrolidinium based ionic liquids and acetonitrile mixtures

The use of molecular solvents has been proposed as a simple solution to reduce the high viscosities of neat ionic liquids (ILs) and extend the practical applications of ILs. A proper understanding of the structure and intermolecular interaction is of vital importance for the design, optimization and synthesis of ILs systems with tailored properties for specific applications. In this work, the structure and hydrogen-bond features of the representative pyrrolidinium/piperidinium based ILs and acetonitrile mixtures were studied by a combination of Fourier-transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations. The v(CN) region is sensitive to the microenvironment and is used as IR probe to detect the structure and hydrogen-bond properties of the two IL–acetonitrile binary systems in the whole concentration range. Positive peaks are observed in the excess IR spectra of v(CN) region which indicates the non-ideality of the mixing process and the formation of hydrogen-bonded complexes in the mixtures. With the help of deconvolution and DFT calculations, the species transformation in the mixing process can be identified from the excess spectra: When x(CD3CN) is less than 0.90, acetonitrile mainly interacts with the ion pairs and ion clusters of the ILs. Ion clusters are all broken out into ion pairs and the interaction complex is mainly ion pair–CD3CN when x(CD3CN) > 0.90. In the whole concentration range, the CD3CN cannot break apart the strong coulombic interactions between the cation and anion, and the individual cation and anion do not exist in the mixtures. All of the hydrogen-bonds in the ion pair/ion cluster–acetonitrile complexes are weak strength, closed shells and electrostatically dominant interactions.

Nickel(II) carbonyl, ammonia, and aceto-nitrile complexes supported by a pyridine dipyrrolide pincer ligand.

The synthesis, isolation and crystal structures of nickel(II) carbonyl, aceto-nitrile and ammonia complexes supported by a dianionic, pyridine dipyrrolide pincer ligand [pyrr2py]2-, namely, carbonyl[2,2'-(pyridine-2,6-di-yl)bis-(3,5-di-p-tolyl-pyrrolido-κN)]-nickel(II), [Ni(C41H33N3)(CO)], ammine[2,2'-(pyridine-2,6-di-yl)bis-(3,5-di-p-tolyl-pyrrolido-κN)]nickel(II), [Ni(C41H33N3)(NH3)], and (aceto-nitrile-κN)[2,2'-(pyridine-2,6-di-yl)bis-(3,5-di-p-tolyl-pyrrolido-κN)]nickel(II), [Ni(C41H33N3)(CH3CN)], as well as the free ligand 2,6-bis-(3,5-di-p-tolyl-pyrrol-2-yl)pyridine, C41H35N3 or [pyrr2py]H2 are reported. The nickel complexes are four-coordinate and adopt a square-planar geometry. The CO stretch of the nickel-bound carbon monoxide ligand of [pyrr2py]Ni(CO) has been observed at 2101 cm-1. The ammonia and aceto-nitrile complexes, [pyrr2py]Ni(NH3) and [pyrr2py]Ni(NCMe) feature all-nitro-gen coordination spheres around nickel consisting of different N-donor ligand types.

A highly selective sequential recognition probe for Zn2+ and HSO4-/H2PO4- based on a diarylethene chemosensor.

A novel diarylethene derivative chemosensor DTP-o connected to Schiff base unit for fluorescent detection of Zn2+ and relay-detection of HSO4-/H2PO4- was designed and synthesized successfully. DTP-o displayed excellent photochromism and fluorometric sensing toward Zn2+ to form DTP-o-Zn2+ complex in acetonitrile with the detection limit of 5.62×10-7M. And the form of DTP-o combined with Zn2+ could further be verified by Job's plot titrations and mass spectrometry analysis. Furthermore, the complex of DTP-o-Zn2+ showed an excellent characteristic of fluorescent relay-response toward HSO4- and H2PO4- with high sensitivity and selectivity. The detection limits for HSO4- and H2PO4- were as low as 3.04×10-8M and 3.41×10-8M, respectively. Moreover, the sensor DTP-o could also be applied to detect Zn2+ on practical samples and test strips with high accuracy.

Soft Scorpionate Hydridotris(2-mercapto-1-methylimidazolyl) borate) Tungsten-Oxido and -Sulfido Complexes as Acetylene Hydratase Models.

A series of WIV alkyne complexes with the sulfur‐rich ligand hydridotris(2‐mercapto‐1‐methylimidazolyl) borate) (TmMe) are presented as bio‐inspired models to elucidate the mechanism of the tungstoenzyme acetylene hydratase (AH). The mono‐ and/or bis‐alkyne precursors were reacted with NaTmMe and the resulting complexes [W(CO)(C2R2)(TmMe)Br] (R=H 1, Me 2) oxidized to the target [WE(C2R2)(TmMe)Br] (E=O, R=H 4, Me 5; E=S, R=H 6, Me 7) using pyridine‐N‐oxide and methylthiirane. Halide abstraction with TlOTf in MeCN gave the cationic complexes [WE(C2R2)(MeCN)(TmMe)](OTf) (E=CO, R=H 10, Me 11; E=O, R=H 12, Me 13; E=S, R=H 14, Me 15). Without MeCN, dinuclear complexes [W2O(μ‐O)(C2Me2)2(TmMe)2](OTf)2 (8) and [W2(μ‐S)2(C2Me2)(TmMe)2](OTf)2 (9) could be isolated showing distinct differences between the oxido and sulfido system with the latter exhibiting only one molecule of C2Me2. This provides evidence that a fine balance of the softness at W is important for acetylene coordination. Upon dissolving complex 8 in acetonitrile complex 13 is reconstituted in contrast to 9. All complexes exhibit the desired stability toward water and the observed effective coordination of the scorpionate ligand avoids decomposition to disulfide, an often‐occurring reaction in sulfur ligand chemistry. Hence, the data presented here point toward a mechanism with a direct coordination of acetylene in the active site and provide the basis for further model chemistry for acetylene hydratase.

Synthesis and characterization of new unsymmetrical diglycolamide extractants for lanthanide ion partitioning: part one—straight-chain alkyl derivatives

Six novel unsymmetrical diglycolamide (UDGA) ligands have been synthesized and evaluated as solvent extraction reagents for the partitioning of lanthanide (Ln) ions from nitrate media. The partitioning of europium between aqueous phases of varying nitric acid concentrations and a UDGA organic phase has been characterized radiometrically. The stoichiometry and phase-transfer equilibrium constants of the Eu-UDGA complexes extracted into the organic phase have been reported. Luminescence spectroscopy investigations have established the relative stability and stoichiometry of the complexes in acetonitrile. These UDGA ligands have displayed enhanced interfacial activity, which has decreased the necessary equilibration time while maintaining high Ln distribution ratios.