C6H4 CH Research Articles

Polyphosphorus compounds derived from P4 conversion with sterically demanding cobalt complexes

The conversion of P4 with [CpBnCo(CO)2] (CpBn = C5(CH2C6H5)5) under thermal conditions gives almost exclusively the P10 complex [(CpBnCo)4(μ4‐η4:η4:η2:η2:η1:η1‐P10)]. However, its reaction with [CpBnCo]n, under mild conditions afforded a mixture of products including the P8 species [(CpBnCo)3(μ3‐η4:η2:η2:η1:η1‐P8)] and a rare Co3 cluster [(CpBnCo)2Co(μ3‐η5:η2:η1:η1‐C40H33)(μ‐H)(μ3‐H)]. The products were studied in solution by multinuclear NMR spectroscopy and mass spectrometry and, for some compounds in the solid state, by single crystal X‐ray diffraction.

One‐dimensional Polymers derived from a Sterically Demanding 1,3‐Diphosphete Complex

AbstractThe 1,3‐disphosphete complex [CpBnCo(η4‐P2C2tBu2)] (1) is prepared from the reaction of the sterically demanding [CpBnCo]n (CpBn=C5(CH2C6H5)5) with tert‐butyl phosphaalkyne (tBu−C≡P). The reaction of 1 with copper halides CuX (X=Cl, Br, I) leads to the formation of one‐dimensional coordination polymers of the general formula [{(CpBnCo)(μ3,η4 : 1 : 1‐(PCtBu)2)}{Cu(μ‐X)}2(MeCN)]n (X=Cl (2), Br (3), I (4)). All compounds are studied in solution by multinuclear NMR spectroscopy and mass spectrometry and in the solid state, by single crystal X‐ray diffraction and 31P{1H} MAS NMR.

Normal vs. Inverted Ordering of Reduction Potentials in [FeFe]-Hydrogenases Biomimetics: Effect of the Dithiolate Bulk.

Three hexacarbonyl diiron dithiolate complexes [Fe2(CO)6(µ-(SCH2)2X)] with different substituted bridgeheads (X = CH2, CEt2, CBn2 (Bn = CH2C6H5)), have been studied under the same experimental conditions by cyclic voltammetry in dichloromethane [NBu4][PF6] 0.2 M. DFT calculations were performed to rationalize the mechanism of reduction of these compounds. The three complexes undergo a two-electron transfer whose the mechanism depend on the bulkiness of the dithiolate bridge, which involves a different timing of the structural changes (Fe-S bond cleavage, inversion of conformation and CO bridging) vs redox steps. The introduction of a bulky group in the dithiolate linker has obviously an effect on normally ordered (as for propanedithiolate (pdt)) or inverted (pdtEt2, pdtBn2) reduction potentials. Et → CH2Ph replacement is not theoretically predicted to alter the geometry and energy of the most stable mono-reduced and bi-reduced forms but such a replacement alters the kinetics of the electron transfer vs the structural changes.

Synthesis and Characterization of Chiral Iridium Complexes Bearing Carbohydrate Functionalized Pyridincarboxamide Ligands and Their Application as Catalysts in the Asymmetric Transfer Hydrogenation of α-Ketoacids in Water

[Cp*IrLnCl] complexes [L1 = (methyl-β-d-glucopyranosid-2-yl)picolinamide, 1; L2 = (methyl-3,4,6-tri-O-acetyl-β-d-glucopyranosid-2-yl)picolinamide, 2; L3 = (2,3,4,6-tetra-O-acetyl-β-d-glucopyranosid-1-yl)picolinamide, 3] have been synthesized and completely characterized in solution, by 1D- and 2D-NMR spectroscopy, and in the solid state, by X-ray single crystal diffractometry. Despite the chirality of the Ln-moiety and metal, a single diastereoisomer is observed for L1 (1) and L2 (2) having a (R)-iridium configuration: the pyranose moiety is oriented in a way to minimize the interactions of the axial protons, vicinal to the amide moiety, and Cp*, with the OMe-group pointing toward the Cp*-ligand and away from Ir–Cl. Such a diastereoisomer is also favored by the establishment of an O–H···Cl–Ir hydrogen bond (2.356 Å) and by the minimization of the steric repulsion between one acetyl moiety of L2 and Cp* and picolinamide ligands in 1 and 2, respectively. DFT calculations computed a stabilization by more than 5.9 and 3.1 kcal/mol of this diastereoisomer with respect to other possible ones. Two interconverting diastereoisomers with different chirality at iridium are instead observed in solution for complex 3 in which −CH2OAc [3a, 63%, (R)] and −OAc [3b, 37%, (S)] moieties, respectively, are oriented toward Cp* and N-arm of picolinamide ligands. Consistently, DFT calculations indicate that 3a and 3b have a comparable stability (ΔE = 1.2 kcal/mol). Complexes 1–3 catalyze the asymmetric transfer hydrogenation of RC(O)C(O)OH to RCH(OH)C(O)OH [R = Ph (PGA), CH2Ph (PPA), CH2(4-OH)C6H4 (HPPA)], using both HCOOH and H3PO3 as hydrogen donor, in water at pH 7 (by phosphate buffer), with excellent chemoselectivity and efficiency (conversion >99%) and moderate to good enantioselectivity (30–70% ee). Utilizing catalyst 3 instead of 2, bearing the pseudoenantiomeric L3 of L2 ligand, causes a reduction of the percentage of the major enantiomer (R) with PGA and an inversion of stereoselectivity from (R) to (S) with PPA and HPPA substrates.

Phosphine-Functionalized Syndiotactic Polystyrenes: Synthesis and Application to Immobilization of Transition Metal Nanoparticle Catalysts.

The precise control of monomer sequence and stereochemistry in copolymerization is of much interest and importance for the synthesis of high performance materials, but studies toward this goal have met with only limited success to date. The coordination polymerization of diphenylphosphinostyrene (p-StPPh2 and o-StPPh2 ) and its copolymerization with styrene (St) by (C5 Me4 SiMe3 )Sc(CH2 C6 H4 NMe2 -o)2 have been achieved for the first time to afford a new series of phosphine functionalized syndiotactic polystyrene. By the design of the polymer structure, the copolymer of o-StPPh2 and St (poly(o-StPPh2 -alt-St)-b-sPS) containing o-StPPh2 and St atactic alternating copolymer block and syndiotactic polystyrene block (sPS) showed excellent thermal stability and chemical resistance. The simple combination of the triphenylphosphine and syndiotactic polystyrene realized the stable immobilization of metal nanoparticles to afford highly robust metal@poly(o-StPPh2 -alt-St)-b-sPS nanocatalysts at high temperature and various atmospheres. The Cu@poly(o-StPPh2 -alt-St)-b-sPS catalyst can serve as a highly efficient heterogeneous catalyst for the synthesis of quinoline derivatives by acceptorless dehydrogenative coupling of o-aminobenzylalcohol with ketones.

Interaction of trans-tetrachlorodi-m-carboxylates of dirhenium(III) with dipeptides of the glycyl series

The paper reports the methods for the synthesis of new cluster compounds of trans-tetrachlorodi--carboxylates of dirhenium(III) with dipeptides of the glycyl series. The compositions and the structures were determined by electron absorption and IR spectroscopies as well as by elemental analysis for the following newly synthesized compounds: trans-[Re2(H3N+–CH2–СO–NH–CH(COO)–CH2–CH(CH3)–CH3)2Cl42СН3CN]Cl2 (І) and trans-[Re2(H3N+–CH2–СO–NH–CH(COO)–CH2–C6H5)2Cl42СН3CN]Cl2 (ІІ). Analysis of the electronic absorption spectra of the solutions of the synthesized substances showed the presence of a doublet pattern (12500 and 16129 сm–1), which corresponds to the *-electronic transition of the Re–Re quadruple bond characteristic of solutions of trans-tetrachlorodi--carboxylates of dirhenium(III). The appearance of oscillations at 1485 сm–1 for І and 1486 сm–1 for ІІ, characteristic of the s(CO) of the coordinated carboxylate group, was detected on the IR spectra, which indicates the bridging coordination of this group to the Re26+ binuclear fragment. The protonation of the amino group is indicated by the appearance of a wide band of valence oscillations (NH3+) in the range of 3400–3350 сm–1 and deformation oscillations (NH3+) at 1557 сm–1 and 1614 сm–1 for I and II, respectively. The stability of the obtained complex compounds in aqueous solutions was determined. It was shown that the hydrolysis of the synthesized substances takes place in 4–5 days, which is accompanied by a decrease in the pH of the reaction solution.

Optical Properties of (C2H5C6H4NH2)2ZnBr2 Complex: Experimental and Quantum Chemical Studies

This study aims to develop a new type of semiconductor material. In this context, the coordination complex (CH3–CH2–C6H4–NH2)2 ZnBr2 material was subjected to UV–Vis spectroscopy and the dependent theoretical density functional theory (TD-DFT) studies. The optical properties such as optical absorption, bandgap, and molecular orbital energies are determined and discussed. The experimental results and theoretical conclusions appear to be in good agreement. Although we checked that the experimental molecular geometry is predicted correctly using the (TD-DFT) method. The molecular electrostatic potential (MEP) was calculated to predict physicochemical properties. The molecular composition of HOMO–LUMO and their bandgap energies are represented to explain the activity of the title compound. So, the studied material seems to have a semiconductor behavior.

Isomerization Dynamics in the Symmetric and Asymmetric Fragmentation of Ethane Dications.

Hydrogen- or proton-migration-induced isomerization has recently been of concern for its critical role in the dissociation of organic molecules of astrophysical or biological relevance. Herein we present a combined experimental and theoretical study of the two-body C-C bond breakdown dissociation of ethane dication. For the asymmetric fragmentation channel CH2+ + CH4+, the kinetic energy release measurements and ab initio quantum chemical calculations demonstrate that the reaction pathway involving hydrogen-migration-induced isomerization of [CH3-CH3]2+ to [CH2-CH4]2+ can be accessed via the lowest triplet state rather than the ground singlet state of ethane dication. Interestingly, it is found that a considerable proportion of the yield of symmetric fragmentation CH3+ + CH3+, which is usually considered from a direct Coulomb explosion and seemingly independent of isomerization, could come from the dissociation of ethane dication in the ground singlet state with the involvement of [CH3-CH3]2+ isomerization to intermediate [H2C(H2)CH2]2+ of the diborane-like double-bridged structure.

Crystal structure of the unusual coordination polymer catena-poly[[gold(I)-μ-1,2-bis-(di-phenyl-phosphino-thio-yl)ethane-κ2 S:S'] di-bromido-aurate(I)

In the title compound, {[Au(C26H24P2S2)][AuBr2]} n , the gold(I) centres of the cation are coordinated by the P=S groups of the di-sulfide ligands to form a chain polymer parallel to the c axis. Both independent gold atoms lie on the same twofold axis, and the midpoint of the H2C-CH2 bond lies on an inversion centre. The anions flank the polymeric chain; they are connected to it by short aurophilic inter-actions and C-H⋯Br contacts, and to each other by Br⋯Br contacts.

Effect of the iron amount on the physicochemical properties of Fe–ZrO2 aerogel catalysts for the total oxidation of Toluene in the presence of water vapor

In this work, a series of xFe–ZrO2 aerogel catalysts, with different amounts of iron were prepared and tested in the total oxidation of toluene. The xFe–ZrO2 aerogel catalysts obtained demonstrate the diffraction peaks of ZrO2 tetragonal phase and a high surface area and porosity. The iron content influences the physicochemical and catalytic properties of the samples. Among the iron-based catalysts, the one with 5% Fe shows the best activity between 300 and 550 °C with 96% C6H5–CH3 conversion to CO2 at 550 °C.

Self-Assembled Quaternary Ammonium-Containing Comb-Like Polyelectrolytes for the Hydrolysis of Organophosphorous Esters: Effect of Head Groups and Counter-Ions.

The aim of this work was to increase the efficiency of catalytic systems for the hydrolytic cleavage of 4-nitrophenyl esters of phosphonic acids. Quaternary ammonium-containing comb-like polyelectrolytes («polymerized micelles») with ester cleavable fragments and a low aggregation threshold were used as catalysts. The synthesis of poly(11-acryloyloxyundecylammonium) surfactants with different counterions (Br- , NO3- , CH3 C6 H4 SO3- ) and head groups was realized by micellar free-radical polymerization. Molecular weight, critical association concentration, particle sizes and solubilization properties toward Orange OT were determined. Self-assemblies organized by poly(11-acryloyloxyundecyltrimethyl ammonium) bromide successfully catalyze the hydrolysis of 4-nitrophenyl butylchloromethylphosphonate up to two orders of magnitude compared to aqueous alkaline hydrolysis. The development of these catalysts is promising for industrial applications and organophosphorus compound detoxification.

A facile and efficient synthesis of benzimidazole as potential anticancer agents

This study reports a simple process to synthesize and separate of 2-(substituted-phenyl) benzimidazole derivatives with high yield and efficiency. Specifically, by reacting ortho-phenylenediamines with benzaldehydes using sodium metabisulphite as an oxidation agent in a mixture of solvent under mild condition, twenty-three compounds of benzimidazoles were obtained and separated easily using hexane and water to wash, respectively. The structure of all obtained compounds was identified by FTIR, NMR and HRMS. The SAR analysis of synthesized benzimidazoles on human lung (A549), breast (MDA-MB-231) and prostate (PC3) cancer cell lines showed that the presence of methyl group at 5(6)-position on benzimidazole scaffold was a contributing factor influencing the anticancer activity. The presence of electron-donating groups (OH, OMe, –NMe2, –O–CH2–C6H5) also caused significant increase of anticancer activity, while the presence of electron-withdrawing groups (–NO2, –CF3) on the phenyl group at 2-position of benzimidazole ring decreased the ability of inhibition of synthesized benzimidazoles. The compounds 2f and 2g displayed the significant anticancer activity on both A549 and PC3 cell lines. Two series of 2-phenylbenzimidazoles were synthesized by simple process with high yield and efficiency and they were illumiated the effect of substituent groups in their structures on the bioactivity against three cancer cell line A549, MDA-MB-231 and PC3.

Syntheses, crystal structures, and characterizations of a series of divalent metal carboxylate-phosphonates

The hydrothermal reactions of divalent metal salts with 4-HOOC–C6H4–CH2–NH2CH2PO3H2 (H3L) led to four Metal-organic phosphonates (MOPs), namely, Ni(HL)(H2O)2 (1), Cd(HL) (2), CdCl(H2L) (3), and Pb1.5Cl2(H2L) (4). All these compounds exhibited 2D layer substructures with various features based on metal centers and –PO3 groups of the ligands. Differently, the layers cross-linked each other in compounds 1 and 4via hydrogen bonds generating 3D supramolecular frameworks. While in compounds 2 and 3, they were connected by carboxylate group of the ligands to form 3D pillared-layer frameworks. Such differences were related to the coordination mode of the metal centers, and the pH of the reaction system also played a important role on the coordination ability of the ligands. The magnetic properties reveal the presence of ferromagnetic interactions in compound 1 through a Ni–O–P–O–Ni five-member chain. Luminescent measurements indicate that compounds 2–4 each displays strong blue fluorescent emissions.

Spin-Forbidden Reactivity of Transition Metal Oxo Species: Exploring the Potential Energy Surfaces.

Spin-forbidden reactions are frequently encountered when transition metal oxo species are involved, particularly in oxygen transfer reactivity. The computational study of such reactions is challenging, because reactants and products are located on different spin potential energy surfaces (PESs). One possible approach to describe these reactions is the so-called minimum energy crossing point (MECP) between the diabatic reactants and products PESs. Alternatively, inclusion of spin-orbit coupling (SOC) effects allows to locate a saddle point on a single adiabatic PES (TS SOC). The TS SOC approach is rarely applied because of its high computational cost. Recently evidence for a TS SOC impact on significantly lowering the activation barrier in dioxygen addition to a carbene-gold(I)-hydride complex reaction (Chem. Sci. 2016, 7, 7034-7039) or even on predicting a qualitatively different reaction mechanism in mercury methylation by cobalt corrinoid (Angew. Chem. Int. Ed. 2016, 55, 11503-11506) has been put forward. Using MECP and TS SOC approaches a systematic analysis is provided here of three prototypical transition metal oxo spin-forbidden processes to investigate their implications on reactivity. Cycloaddition of ethylene to chromyl chloride (CrO2 Cl2 +C2 H4 ), iron oxide cation insertion into the hydrogen molecule (FeO+ +H2 ) and H-abstraction from toluene by a MnV -oxo-porphyrin cation (MnOP(H2 O)+ +C6 H5 CH3 ) are case studies. For all these processes the MECP and TS SOC results are compared, which show that the spin-forbidden reactivity of transition metal oxo species can be safely described by a MECP approach, at least for the first-row transition metals investigated here, where the spin-orbit coupling is relatively weak. However, for the Mn-oxo reactivity, the MECP and TS SOC have been found to be crucial for a correct description of the reaction mechanism. In particular, the TS SOC approach allows to straightforwardly explore detailed features of the adiabatic potential energy surface which in principle could affect the overall reaction rate in cases where the involved diabatic PESs are tricky.

Magnetic Field Directed Rare-Earth Separations.

The separation of rare-earth ions from one another is challenging due to their chemical and physical similarities. Nearly all rare-earth separations rely upon small changes in ionic radii to direct speciation or reactivity. Herein, we show that the intrinsic magnetic properties of the rare-earth ions impact the separations of light/heavy and selected heavy/heavy binary mixtures. Using TriNOx3- ([{(2-t BuNO)C6 H4 CH2 }3 N]3- ) rare-earth complexes, we efficiently and selectively crystallized heavy rare earths (Tb-Yb) from a mixture with light rare earths (La and Nd) in the presence of an external Fe14 Nd2 B magnet, concomitant with the introduction of a concentration gradient (decrease in temperature). The optimal separation was observed for an equimolar mixture of La:Dy, which gave an enrichment factor of EFLa:Dy =297±31 for the solid fraction, compared to EFLa:Dy =159±22 in the absence of the field, and achieving a 99.7 % pure Dy sample in one step. These results indicate that the application of a magnetic field can improve performance in a molecular separation system for paramagnetic rare-earth cations.

Ferrocenoyl conjugates of hydroxyl group containing side chain amino acids: Synthesis, electrochemical study and reactivity toward electrophiles

Mono- and disubstituted ferrocenoyl amino acid conjugates having free hydroxyl (OH) group at the amino acid side chain is synthesized, namely Fc–CO–aa-OCH3 (1a, 2a, 3a), and Fc-[CO-aa-OCH3]2 (1b, 2b, 3b), Fc = ferrocene, aa = l-serine (L-Ser, 1), l-tyrosine (L-Tyr, 2), l-threonine (L-Thr, 3). The reactivity of the OH group in 1a toward substitution reaction by acetyl chloride, p-toluene sulfonyl chloride and phosphoric acid is investigated. The resulting compounds are Fc–CO–L-Ser(C(O)–CH3)–OCH3 (1c), Fc–CO–L-Ser(S(O)2–C6H4–CH3)–OCH3 (1d) and Fc–CO–L-Ser(P(O)–(OH)2)–OCH3 (1e). The prepared Fc-amino acid conjugates are fully characterized by standard spectroscopic methods. The cyclic voltammetry of the Fc-compounds show a quasi-reversibility for conjugates 1a-3a (E1/2 = 0.64 V) and for 1b, 3b (E1/2 = 0.85 V), while an irreversible behavior for 2b is observed. The compounds 1c and 1d exhibit quasi-reversibility with E1/2 = 0.71 V, which is shifted anodically by 100 mV compared to the parent conjugate 1a. Fc-conjugate 1e shows complete irreversibility. The study suggests that profound changes in Fc-redox potential is accessible through varying the substituent at the OH group in the amino acid side chain, either by anodic shift of the Fc signal (acylation and tosylation) or turn the signal off by phosphorylation.

A new hybrid layered perovskite [CH3–C6H4–NH3]2ZnBr4: Synthesis, crystal structure, optical and electrical properties

Low dimensional hybrid metal halides [CH3–C6H4–NH3]2ZnBr4 were synthesized by slow evaporation method at room temperature. The single crystal structure of the organic–inorganic metal halides [CH3–C6H4–NH3]2ZnBr4 has been investigated. The structure of [CH3–C6H4–NH3]2ZnBr4 belongs to the triclinic space group P-1, with a = 7.1148(3) Å, b = 11.5750(5) Å, c = 12.5024(6) Å, α = 107.236(2)°, β = 95.412(3)° and γ = 91.506(2)°. The bis-(p-toluidinium) tetrabromozincate (II) structure features well-ordered layers of isolated ZnBr4 separated by bilayers of p-toluidinium cations. Thermal analysis was studied and showed one anomaly at 280 K which can be attributed to the phase transition in this material. Optical properties allows to extracted the gap energy where is equal to 3.28eV. The electrical properties used to determinate the equivalent circuit and activation energy by the variation of σg and σdc. The exponent S indicates that the OLPT is the conduction mechanism described the conduction of this material.

Conformational Effects of [Ni2 (μ-ArS)2 ] Cores on Their Electrocatalytic Activity.

Two nickel complexes supported by tridentate NS2 ligands, [Ni2 (κ-N,S,S,S'-NPh {CH2 (MeC6 H2 R')S}2 )2 ] (1; R'=3,5-(CF3 )2 C6 H3 ) and [Ni2 (κ-N,S,S,S'-NiBu {CH2 C6 H4 S}2 )2 ] (2), were prepared as bioinspired models of the active site of [NiFe] hydrogenases. The solid-state structure of 1 reveals that the [Ni2 (μ-ArS)2 ] core is bent, with the planes of the nickel centers at a hinge angle of 81.3(5)°, whereas 2 shows a coplanar arrangement between both nickel(II) ions in the dimeric structure. Complex 1 electrocatalyzes proton reduction from CF3 COOH at -1.93 (overpotential of 1.04 V, with icat /ip ≈21.8) and -1.47 V (overpotential of 580 mV, with icat /ip ≈5.9) versus the ferrocene/ferrocenium redox couple. The electrochemical behavior of 1 relative to that of 2 may be related to the bent [Ni2 (μ-ArS)2 ] core, which allows proximity of the two Ni⋅⋅⋅Ni centers at 2.730(8) Å; thus possibly favoring H+ reduction. In contrast, the planar [Ni2 (μ-ArS)2 ] core of 2 results in a Ni⋅⋅⋅Ni distance of 3.364(4) Å and is unstable in the presence of acid.

Benzyl Borane NHC Adducts: Beyond B-C Bond Scission.

Benzyl-substituted boronates and borates are widely employed as mild sources in radical or anionic transfer reactions of benzyl entities. In this process the B-C bond to the benzyl moiety is essentially ruptured. In contrast, reactions with retention of the B-C bond are poorly investigated although several other reactive sites in benzyl-boron systems are clearly inherent. In this respect, the novel reactivity of the representative borane adduct IiPr-BH2 Bn [IiPr=:C{N(iPr)CH}2 , Bn=CH2 C6 H5 ] is demonstrated. Dihalogenation of the BH2 entity is observed with BCl3 and BBr3 , whereas BI3 either affords IiPr-BHI2 or proceeds with borylation of the aromatic phenyl ring to give a hydride-bridged bisborylated species. The photochemical mono- and dihalogenation of the benzylic CH2 group was demonstrated with elemental bromine Br2 . The brominated product IiPr-BBr2 -CHBr-C6 H5 was borylated at the benzylic carbon atom in an umpolung event with BI3 to afford the zwitterion IiPr-BI-CH(BI3 )-C6 H5 .

Syndiospecific Coordination Polymerization of Si-H-Containing Styrenes Catalyzed by Scandium Complex and Synthesis of Styrene-Based Triblock Copolymers.

The controlled syndiospecific polymerization of three Si-H-containing styrenes, that is, 4-(methylhydrosilyl)styrene (FSt-1), 4-(dimethylhydrosilyl)styrene (FSt-2) and 4-(diisopropylhydrosilyl)styrene (FSt-3), is realized in the presence of (C5 Me4 SiMe3 )Sc (CH2 C6 H5 )2 (THF)/[Ph3 C][B(C6 F5 )4 ]. Then a series of FSt-b-styrene-b-FSt triblock copolymers (FSt-St-FSt) are synthesized facilely via a sequential monomer feeding process (FSt-2, styrene, and FSt-2, respectively) during the polymerization. The syndiotactic polystyrene (sPS) block in the middle endows the copolymer with high melting point above 250 °C, whereas the Si-H groups on monomer FSt-2 introduce functional pendants to the end-blocks (with Si-H content of 31-63 mol%). Finally by a mild and high-effective hydrosilylation reaction, novel polar-group functionalized sPS is obtained.