CH CN Research Articles

Activation of Acetonitrile with (C2 F5 )3 PF2 and Amines.

Acetonitrile is deprotonated by a combination of the strong Lewis acid (C2 F5 )3 PF2 and triethylamine. The resulting cyanomethyl function is bound to the phosphorus moiety, affording the highly stable salt [HNEt3 ][P(C2 F5 )3 F2 (CH2 CN)]. Salt metathesis reactions furnished the corresponding [Cu(MeCN)2 ]+ and [Ag(MeCN)]+ derivatives in which the CH2 CN substituent of the anion [P(C2 F5 )3 F2 (CH2 CN)]- coordinates to the metal. An investigation of the gas separation capability of the silver salt [Ag(MeCN)][P(C2 F5 )3 F2 (CH2 CN)] shows an uptake of 1.7 equivalents of isobutene from a propane/isobutene mixture. The reaction of (C2 F5 )3 PF2 with acetonitrile and diethylamine furnishes [P(C2 F5 )3 F2 {NHC(CH3 )NEt2 }]-a phosphate featuring an amidine ligand which formally results from hydroamination of acetonitrile by HNEt2 . Exchange of HNEt2 with the primary amines H2 NPh and H2 NBu leads to comparable amidine salts that exhibit a solvent-dependent conformational isomerism.

Macrocycles Bearing Ferrocenyl Pendants and their Electrochemical Properties upon Binding to Divalent Transition Metal Cations.

Metal complexes of Cu2+ , Co2+ , Cd2+ , Zn2+ , and Ni2+ formed with the ligands [Fc(cyclen)] (1) and [Fc(cyclen)2 ] (2) (Fc=ferrocene, cyclen=1,4,7,10-tetraazacyclododecane) are synthesised and characterised. The X-ray structure of the Cu2+ complex of 2, Fc([Cu(cyclen)(CH3 CN)]2 (ClO4 )4 , is reported, and shows that the two positively charged Cu2+ -cyclen units have a coordination number of five, adopting a distorted trigonal-bipyramidal configuration. The Cu2+ -cyclen units are arranged in a trans-like configuration with respect to the Fc group, presumably to minimise electrostatic repulsion. The voltammetric oxidation of the free ligands 1 and 2 in a CH2 Cl2 /CH3 CN (1:4) solvent mixture yields two closely spaced oxidation processes. Both electron-transfer steps are associated with the ferrocenyl moiety, implying strong communication between the cyclen nitrogen atoms and the ferrocenyl group. In contrast, cyclic voltammograms display only a simple reversible one-electron process if 1 and 2 are complexed with Cd2+ , Cu2+ , Zn2+ , Ni2+ , or Co2+ . Binding of these metal ions produces a significant shift in the reversible midpoint potential (Em ). Except for Ni2+ , Em is linearly proportional to the charge density of the transition metal ion, demonstrating that 1 and 2 may undergo redox switching. The diffusion coefficients of Fc, DmFc, 1 and 2, and their metal ion complexes correlate well with their molecular weights.

Enantiomeric resolution and modeling of DL‐alanine‐DL‐tryptophan dipeptide on amylose stationary phase

The enantiomeric resolution of DL-alanine-DL-tryptophan dipeptide is described on amylose stationary phase. The eluent used was CH3 OH─CH3 COONH4 (10mM)─CH3 CN (50: 40, 10) at 0.8-mL/min flow, 230-nm detection, 25-minute run time, and 25°C±1°C temperature. The chiral phase was amylose [AmyCoat RP (15cm×0.46cm×5micron)]. The magnitudes of the retention factors (k) were 2.71, 3.52, 5.11, and 7.75. The magnitudes of separation factor (α) were 1.19, 1.57, and 1.51 while the resolution factors (Rs) were 3.25, 14.84, and 15.76. The limits of detection and quantitation were of 2.5 to 5.4 and 12.8 to 27.5μg/mL. The enantiomeric resolution is controlled by hydrogen, hydrophobic, π-π, steric, etc interactions. The elution order of the enantiomer was supported by the modeling data. The described method is fast, reproducible, precise, and selective, which can be used successfully for evaluating the enantiomers of the reported dipeptide.

Valence Localization at a Bio-inspired Mixed-Valent {Cu2 S}2+ Motif upon Solvation in Acetonitrile: Effect on Nitrous Oxide Reductase (N2 Or) Activity.

We demonstrate, based on experimental and theoretical evidence, that the isolated [2(CH3 CN)2 ]2+ complex prepared in CH3 CN and containing a mixed-valent {Cu2II,I S} core evolves towards a new [2(CH3 CN)3 ]2+ species upon solvation in CH3 CN. Unlike its type III structural analogue [2(H2 O)(OTf)]+ active toward N2 O reduction, this new type I compound is inactive. This outcome opens new perspectives for a rational for N2 O activation using bio-inspired Cu/S complexes, especially on the role of the valence localization/delocalization and the Cu-Cu bond on the reactivity.

Construction of Zeolite-Like Cluster Organic Frameworks from 3 d-4 d/3 d-3 d Heterometallic Supertetrahedral Secondary Building Units: Syntheses, Structures, and Properties.

Two zeolite-like cluster organic frameworks based on Cd-Cu/Mn-Cu heterometallic supertetrahedral secondary building units have been successfully constructed under solvothermal conditions, namely, Cu[Cd4 Cu6 (L)4 (H2 O)18 ](Ac)9 ⋅DMA⋅3 H2 O (1), and Cu[Mn4 Cu6 (L)4 (Ac)3 (H2 O)12 ](Ac)6 ⋅CH3 CN⋅13 H2 O (2), where H3 L=2-(hydroxymethyl)-2-(pyridin-4-yl)-1,3-propanediol, Ac=CH3 COO- , DMA=N,N'-dimethylacetamide. Single-crystal X-ray structural analysis reveals that both 1 and 2 exhibit 3-dimensional zeolite-like architectures with similar 4-connected components, but possess definitely different topologies of diamondoid (dia) and uncommon lonsdaleite (lon), respectively. 1 and 2 represent the first cases of zeolite-like cluster organic frameworks containing Cd-Cu/Mn-Cu heterometallic supertetrahedral secondary building units. Furthermore, the magnetic properties and porous nature of 1 and 2 were also studied.

A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N3 O Macrocyclic Ligand.

The sluggish oxidants [FeIV (O)(TMC)(CH3 CN)]2+ (TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and [FeIV (O)(TMCN-d12 )(OTf)]+ (TMCN-d12 =1,4,7,11-tetra(methyl-d3 )-1,4,7,11-tetraazacyclotetradecane) are transformed into the highly reactive oxidant [FeIV (O)(TMCO)(OTf)]+ (1; TMCO=4,8,12-trimethyl-1-oxa-4,8,12-triazacyclotetradecane) upon replacement of an NMe donor in the TMC and TMCN ligands by an O atom. A rate enhancement of five to six orders of magnitude in both H atom and O atom transfer reactions was observed upon oxygen incorporation into the macrocyclic ligand. This finding was explained in terms of the higher electrophilicity of the iron center and the higher availability of the more reactive S=2 state in 1. This rationalizes nature's preference for using O-rich ligand environments for the hydroxylation of strong C-H bonds in enzymatic reactions.

Photocatalytic Conversion of CO2 to CO by a Copper(II) Quaterpyridine Complex.

The invention of efficient systems for the photocatalytic reduction of CO2 comprising earth-abundant metal catalysts is a promising approach for the production of solar fuels. One bottleneck is to design highly selective and robust molecular complexes that are able to transform the CO2 gas. The CuII quaterpyridine complex [Cu(qpy)]2+ (1) is found to be a highly efficient and selective catalyst for visible-light driven CO2 reduction in CH3 CN using [Ru(bpy)3 ]2+ (bpy: bipyridine) as photosensitizer and BIH/TEOA (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole/triethanolamine) as sacrificial reductant. The photocatalytic reaction is greatly enhanced by the presence of H2 O (1-4 % v/v), and a turnover number of >12 400 for CO production can be achieved with 97 % selectivity, which is among the highest of molecular 3d CO2 reduction catalysts. Results from Hg poisoning and dynamic light scattering experiments suggest that this photocatalyst is homogenous. To the best of our knowledge, 1 is the first example of molecular Cu-based catalyst for the photoreduction of CO2 .

Homo- and Heterobinuclear Cu and Pd Complexes with a Bridging Redox-Active Bisguanidino-Substituted Dioxolene Ligand: Electronic Structure and Metal-Ligand Electron-Transfer.

A new redox-active 4,5-bisguanidino-substituted o-benzoquinone ligand L is synthesized, which allows rational access to heterobinuclear complexes through the sequential coordination of two metals. In the examples discussed in this work, mononuclear Cu and Pd complexes are prepared in a first coordination step, and these complexes are then used as precursors to homobinuclear [CuII -L0 -CuII ] and heterobinuclear [PdII -L0 -CuII ] complexes. In the heterobinuclear complex, the PdII is coordinated by the softer bisguanidine side of L and the CuII by the harder dioxolene side (in line with the HSAB concept). The heterobinuclear complex is in a temperature-dependent equilibrium with its dimer, with two unsymmetrical Cu-Cl-Cu bridges. The redox-chemistry of the [CuII -L-CuII ] and [PdII -L-CuII ] complexes is studied. One-electron oxidation of both complexes was found to be quasi-reversible in CV experiments, and chemical one-electron oxidation was achieved with NO+ (SbF6- ). In the case of the homobinuclear complex [L(CuCl2 )2 ]+ , intramolecular ligand-metal electron-transfer, triggered by coordination of a CH3 CN solvent molecule, leads to a temperature-dependent equilibrium between the form [CuII -L0 -CuIII ] at low temperatures (with CH3 CN coordinated to the CuIII atom) and [CuII -L⋅+ -CuII ] at higher temperatures (without CH3 CN).

Insights into Magnetic Interactions in a Monodisperse Gd12 Fe14 Metal Cluster.

The largest Ln-Fe metal cluster [Gd12 Fe14 (μ3 -OH)12 (μ4 -OH)6 (μ4 -O)12 (TEOA)6 (CH3 COO)16 (H2 O)8 ]⋅(CH3 COO)2 (CH3 CN)2 ⋅(H2 O)20 (1) and the core-shell monodisperse metal cluster of 1 a@SiO2 (1 a=[Gd12 Fe14 (μ3 -OH)12 (μ4 -OH)6 (μ4 -O)12 (TEOA)6 (CH3 COO)16 (H2 O)8 ]2+ ) were prepared. Experimental and theoretical studies on the magnetic properties of 1 and 1 a@SiO2 reveal that encapsulation of one cluster into one silica nanosphere not only effectively decreases intermolecular magnetic interactions but also significantly increases the zero-field splitting effect of the outer layer Fe3+ ions.

Synthesis, Characterization, and Efficient Catalytic Activities of a Nickel(II) Porphyrin: Remarkable Solvent and Substrate Effects on Participation of Multiple Active Oxidants

A new nickel(II) porphyrin complex, [NiII (porp)] (1), has been synthesized and characterized by 1 H NMR, 13 C NMR and mass spectrometry analysis. This NiII porphyrin complex 1 quantitatively catalyzed the epoxidation reaction of a wide range of olefins with meta-chloroperoxybenzoic acid (m-CPBA) under mild conditions. Reactivity and Hammett studies, H218 O-exchange experiments, and the use of PPAA (peroxyphenylacetic acid) as a mechanistic probe suggested that participation of multiple active oxidants NiII -OOC(O)R 2, NiIV -Oxo 3, and NiIII -Oxo 4 within olefin epoxidation reactions by the nickel porphyrin complex is markedly affected by solvent polarity, concentration, and type of substrate. In aprotic solvent systems, such as toluene, CH2 Cl2 , and CH3 CN, multiple oxidants, NiII -(O)R 2, NiIV -Oxo 3, and NiIII -Oxo 4, operate simultaneously as the key active intermediates responsible for epoxidation reactions of easy-to-oxidize substrate cyclohexene, whereas NiIV -Oxo 3 and NiIII -Oxo 4 species become the common reactive oxidant for the difficult-to-oxidize substrate 1-octene. In a protic solvent system, a mixture of CH3 CN and H2 O (95:5), the NiII -OOC(O)R 2 undergoes heterolytic or homolytic O-O bond cleavage to afford NiIV -Oxo 3 and NiIII -Oxo 4 species by general acid catalysis prior to direct interaction between 2 and olefin, regardless of the type of substrate. In this case, only NiIV -Oxo 3 and NiIII -Oxo 4 species were the common reactive oxidant responsible for olefin epoxidation reactions.

Silver(I) Clusters with Carba-closo-dodecaboranylethynyl Ligands: Synthesis, Structure, and Phosphorescence.

Salts of anionic silver(I) clusters with the carba-closo-dodecaboranylethynyl ligand were obtained from {Ag2 (12-C≡C-closo-1-CB11 H11 )}n , selected pyridines, and [Et4 N]Cl or [Ph4 P]Br. Salts of octahedral silver(I) clusters [Et4 N]2 [Ag6 (12-C≡C-closo-1-CB11 H11 )4 (4-X-C5 H5 N)x ] were formed with pyridine (X=H, x=8), 4-methylpyridine (X=Me, x=8), and 4-cyanopyridine (X=CN, x=10). In contrast, 3,5-lutidine (3,5-Me2 Py) did not result in salts of dianionic clusters, even in the presence of excess of [Et4 N]Cl or [Ph4 P]Br; instead salts of monoanionic AgI7 clusters, [Et4 N][Ag7 (12-C≡C-closo-1-CB11 H11 )4 (3,5-Me2 Py)9 ] and [Ph4 P][Ag7 (12-C≡C-closo-1-CB11 H11 )4 (3,5-Me2 Py)13 ] were obtained. The AgI7 cluster is pentagonal bipyramidal in the former, but is an edge-capped octahedron in the latter. The 4-methylpyridine and 3,5-lutidine complexes show green phosphorescence at room temperature. Although argentophilic interactions give rise to sufficient spin-orbit coupling for intersystem crossing S1 →Tn and moderate-to-high radiative rate constants, time-resolved measurements indicate that the quantum yields are greatly influenced by the pyridine ligands, which mainly determine the non-radiative rate constants. In addition, the crystal structures of [Ag16 (12-C≡C-closo-1-CB11 H11 )8 (Py)9.25 (CH3 CN)2 (CH2 Cl2 )0.75 ]⋅CH2 Cl2 , [Ag8 (12-C≡C-closo-1-CB11 H11 )4 (Py)12 ], [Ag10 (12-C≡C-closo-1-CB11 H11 )4 (4-MePy)10 Br2 ], [Ag7 (12-C≡C-closo-1-CB11 H11 )3 (4-tBuPy)11 Cl]⋅(4-tBuPy), and [Ag9 (12-C≡C-closo-1-CB11 H11 )4 (3,5-Me2 Py)11 Cl] were elucidated.

Correlation of mesogenic properties with intermolecular interaction energy for homologous series of HnCBP

ABSTRACTIntermolecular interaction energy between a pair of molecules of homologous series 4, 4′-disubstituted biphenyl of the general formula HO‒(CH2)n‒O‒C6H4‒C6H4‒CN(n = 3 − 11) (HnCBP) has been evaluated under various interacting conditions viz. stacking, in-plane and terminal interaction. Molecular geometry of the studied molecules was fully optimized without any constraint and checked for imaginary frequencies using hybrid density functional B3LYP combined with 6–31 g** basis set. Electronic structure of the molecules obtained through these calculations has been utilized to calculate electrostatic and polarization energies under Rayleigh-Schrodinger perturbation theory modified with multi-centered multi-pole expansion method. Dispersion and repulsion energies have been evaluated using Kitaigorodskii formula. The identified minimum energy complexes have been further utilized to evaluate interaction energy under super molecular approach by employing M06 and DFT-D methods. A comparative analysis of the results has been reported with a view to examine suitability of different methods to study molecular aggregations in moderately large organic systems.

The CN–CH Positive Correlation in the Globular Cluster NGC 5286

Abstract We performed low-resolution spectroscopy of the red giant stars in the Galactic globular cluster (GC) NGC 5286, which is known to show intrinsic heavy element abundance variations. We found that the observed stars in this GC are clearly divided into three subpopulations by CN index (CN-weak, CN-intermediate, and CN-strong). The CN-strong stars are also enhanced in the calcium HK′ (7.4σ) and CH (5.1σ) indices, while the CN-intermediate stars show no significant difference in the strength of the HK′ index from the CN-weak stars. From the comparison with high-resolution spectroscopic data, we found that the CN- and HK′-strong stars are also enhanced in the abundances of Fe and s-process elements. It appears, therefore, that these stars are later-generation stars affected by some supernova enrichment in addition to the asymptotic giant branch ejecta. In addition, unlike normal GCs, sample stars in NGC 5286 show the CN–CH positive correlation, strengthening our previous suggestion that this positive correlation is only discovered in GCs with heavy element abundance variations, such as M22 and NGC 6273.

Theoretical studies of the copper gyromagnetic factors for three novel Cu2+ coordination polymers with bi-triazole ligand.

The copper electron paramagnetic resonance gyromagnetic factors are theoretically studied for three novel Cu2+ coordination polymers [Cu(XL)(NO3 )2 ]n (1), {[Cu(XL)(4,4'-bpy)(NO3 )2 ]•CH3 CN}n (1a) and {[Cu(XL)3 ](NO3 )2 •3.5H2 O}n (2) with bi-triazole ligand (XL)=N,N'-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxdiimide bi(1,2,4-triazole) from the high-order perturbation calculations of the g factors for a rhombically elongated octahedral 3d9 group. The order (1≤1a<2) of gz can be illustrated by the dominant second-order perturbation term roughly proportional to the square of the covalency factor N. gx (and gy ) relies on the combination of the contributions from N, cubic field parameter Dq , and axial elongation of the copper sites and exhibits the sequence (1≤2<1a). As regards the axiality (gx ≈gy ) of g factors, this is because the perpendicular rhombic contribution from the deviations of the bond lengths and bond angles for the planar ligands with respect to an ideal octahedron and that from the discrepancies between the crystal fields of the planar ligands O2- and N3- largely cancel each other. The present theoretical studies on the copper electron paramagnetic resonance g factors would be helpful to understand the structures and properties of some promising coordination polymers containing copper with the novel bi-triazole ligand XL.

Exceptionally Long-Lived Photodriven Multi-Electron Storage without Sacrificial Reagents.

Photoexcitation of a molecular pentad in the presence of Sc3+ in de-aerated CH3 CN leads to a quinone dianion that is stable on the millisecond timescale. Light-driven electron accumulation on the quinone unit is sensitized by two Ru(bpy)32+ complexes in an intramolecular process, which relies on covalently attached triarylamine donors rather than on sacrificial reagents. Lewis acid-Lewis base interactions between Sc3+ and quinone dianion are responsible for the exceptionally long lifetime of this photoproduct. Our study of photoinduced multi-electron transfer is relevant in the greater context of solar energy conversion.

Bimetallic Cooperativity in Proton Reduction with an Amido‐Bridged Cobalt Catalyst

The bimetallic catalyst [CoII2 (L1 )(bpy)2 ]ClO4 (1), in which L1 is an [NN'2 O2 ] fused ligand, efficiently reduced H+ to H2 in CH3 CN in the presence of 100 equiv of HOAc with a turnover number of 18 and a Faradaic efficiency of 94 % after 3 h of bulk electrolysis at -1.6 V (vs. Ag/AgCl). This observation allowed the proposal that this bimetallic cooperativity is associated with distance, angle, and orbital alignment of the two Co centers, as promoted by the unique Co-Namido -Co environment offered by L1 . Experimental results revealed that the parent [CoII CoII ] complex undergoes two successive metal-based 1 e- reductions to generate the catalytically active species [CoI CoI ], and DFT calculations suggested that addition of a proton to one CoI triggers a cooperative 1 e- transfer by each of these CoI centers. This 2 e- transfer is an alternative route to generate a more reactive [CoII (CoII -H- )] hydride, thus avoiding the CoIII -H- required in monometallic species. This [CoII (CoII -H- )] species then accepts another H+ to release H2 .

Vibrational Energy Transfer Dynamics of HCO2CH3 in CH3CN Solution

Vibrational Energy Transfer Dynamics of <scp>HCO₂CH₃</scp> in <scp>CH₃CN</scp> Solution

A Fluxional Cu8 H6 Cluster Supported by Bis(diphenylphosphino)methane and its Facile Reaction with CO2.

A copper hydride cluster [Cu8 (μ-H)6 (μ-dppm)5 ](PF6 )2 (dppm=bis(diphenylphosphino)methane) was prepared from reaction of [CuH(PPh3 )]6 with dppm in the presence of [Cu(CH3 CN)4 ]PF6 and exhibited fluxional behaviors in solution where the hydrides and the phosphines are scrambling around the trans-bicapped octahedral Cu8 framework. The Cu8 H6 complex showed facile reactivity with CO2 (1 atm, RT) to afford a tricopper complex, [Cu3 (μ-H)(μ-O2 CH)(μ-dppm)3 ]PF6 , which could be developed to unprecedented hydrosilylation of CO2 catalyzed by multinuclear CuH species under mild conditions.

Superacids Based on Pentafluoroorthotellurate Derivatives of Aluminum.

The new Lewis acid Al(OTeF5 )3 and its acetonitrile adduct CH3 CN→Al(OTeF5 )3 were obtained by a simple one-step synthesis in batches of up to 15 g. Al(OTeF5 )3 and the adduct were characterized by vibrational spectroscopy (IR, Raman) and quantum-chemical calculations. Furthermore, five different salts of the new weakly coordinating anion [Al(OTeF5 )4 ]- were prepared in a two-step procedure. [Ph4 P][Al(OTeF5 )4 ], Cs[Al(OTeF5 )4 ], [Ph3 C][Al(OTeF5 )4 ], as well as the protonated benzene derivatives [C9 H13 ][Al(OTeF5 )4 ] and [C6 H7 ][Al(OTeF5 )4 ] were characterized by low-temperature single-crystal X-ray diffraction and NMR spectroscopy. Arenium salts have rarely been characterized in the solid state and were synthesized in this work in a simplified fashion.

Control of Product Distribution and Mechanism by Ligation and Electric Field in the Thermal Activation of Methane.

An unexpected mechanistic switch as well as a change of the product distribution in the thermal gas-phase activation of methane have been identified when diatomic [ZnO].+ is ligated with acetonitrile. Theoretical studies suggest that a strong metal-carbon attraction in the pristine [ZnO].+ species plays an important role in the rebound of the incipient CH3. radical to the metal center, thus permitting the competitive generation of CH3. , OH. , and CH3 OH. This interaction is drastically weakened by a single CH3 CN ligand. As a result, upon ligation the proton-coupled single electron transfer that prevails for [ZnO].+ /CH4 switches to the classical hydrogen-atom-transfer process, thus giving rise to the exclusive expulsion of CH3. . This ligand effect can be modeled quite well by an oriented external electric field of a negative point charge.