Cationic palladium(II)–acetylacetonate complexes bearing α-diimine ligands as catalysts in norbornene polymerization

A variety of palladium(II)–acetylacetonate complexes bearing α-diimine ligands were synthesized by the reaction of [Pd(acac)(MeCN)₂]BF₄ with N⁀N ligands. When activated with BF₃·OEt₂, these complexes provide access to a new class of alkylating agent free Pd–diimine catalyst systems. Catalyst screening for the vinyl addition polymerization of norbornene showed their high activities of 10²–10⁴ kg_pol mol_cat^− 1 h^− 1.     

Application of nickel(II) complexes to the efficient synthesis of α- or β-amino acids

Nonproteinogenic α- or β-amino acids have attracted tremendous attention, as they are widely utilized for biological, biochemical, pharmaceutical, and asymmetric chemical investigations. Recently, we developed a series of new strategies for preparing achiral and chiral nickel(ii) complexes for the synthesis of amino acids. We applied these new methods utilizing chiral nickel(ii) complexes for the asymmetric Mannich reaction to synthesize enantiopure α,β-diamino acids, the enantioselective tandem conjugate addition-elimination reaction to prepare glutamic acid derivatives, the Suzuki coupling reaction to yield β(2)-amino acid derivatives, the asymmetric Mannich reaction to synthesize 3-aminoaspartate, the asymmetric Michael addition reaction to give β-substituted-α,γ-diaminobutyric acid derivatives, the asymmetric alkylation reaction to prepare linear ω-trifluoromethyl containing amino acids, and the asymmetric Michael addition reaction to synthesize syn-β-substituted tryptophans.     

Tris(N,N′-dimethylurea)bis(nitrato-O,O′)manganese(II), the first example of a seven-coordinate manganese(II) complex with a monodentate organic ligand

Employing a variety of solvents and molar ratios, the reactions of Mn(NO₃)₂·6H₂O with N,N′-dimethylurea (DMU) afforded the adduct [Mn(NO₃)₂(DMU)₃] (1). X-ray analysis shows that the high-spin complex has a pentagonal bipyramidal geometry with two DMU oxygen atoms in axial positions and with two types of monodentate O-bonding for the DMU molecules, one of them being very unusual. The spectroscopic properties of the prepared complex are also discussed.     

Facile separation of diastereo-chiral N,N′-diamine ligand via fractional crystallization and demetalation of corresponding Zn(II) complex

Enantiopure N,N-diamine has been obtained in an economical manner via demetalation of its corresponding dichloro Zn(II) complex, which is separated by fractional crystallization of two diastereomeric Zn(II) complexes. Polymerization of rac-lactide (rac-LA) initiated by diisopropoxide derivative proceeds rapidly at room temperature in a living fashion to yield heterotactic polylactide (PLA) with P_r = 0.90.     

Directed evolution of (βα)(8)-barrel enzymes: establishing phosphoribosylanthranilate isomerisation activity on the scaffold of the tryptophan synthase α-subunit

Phosphoribosylanthranilate (PRA) isomerase (TrpF) and tryptophan synthase α-subunit (TrpA) are (βα)(8)-barrel enzymes that are involved in the biosynthesis of tryptophan. They contain a conserved phosphate binding site, which indicates a common evolutionary origin. In order to experimentally back this hypothesis, we have established TrpF activity on the scaffold of TrpA from Salmonella typhimurium using protein engineering. Based on the superposition of crystal structures with bound ligands, two residues in the active site of TrpA were replaced with catalytic residues from TrpF using site-directed mutagenesis. This TrpA variant as well as wild-type TrpA were each subjected to random mutagenesis using error-prone PCR. The two resulting trpA gene libraries were used to transform an auxotrophic Escherichia coli trpF deletion strain, and TrpA variants with PRA isomerisation activity were isolated by in vivo complementation. The amino acid substitutions of the selected TrpA variants were recombined by DNA shuffling, again followed by complementation in vivo. Several TrpA variants were produced in E. coli and purified, and their catalytic TrpF activities were determined in vitro by steady-state enzyme kinetics. Our results support that TrpA and TrpF have evolved by gene duplication and diversification from each other or a common predecessor, and provide insights into the minimum requirements for the catalysis of PRA isomerisation.     

The formation of σ-phenylethynyl and σ-diphenylbutenynyl complexes in the reaction of σ-alkenyl ruthenium(II) complexes with phenylacetylene. The X-ray structure of a ruthenium(II) complex containing a σ-phenylethynyl ligand

Ruthenium(II) complexes containing both σ-alkenyl and η²-carboxylate ligands Ru(O₂CR²)(CHCHR¹)(CO)(PPh₃)₂ (R¹^tBu, Ph; R²=CHCHCHCHCH₃) react with phenylacetylene in two stages. Their reaction with an equivalent amount of the alkyne led to the formation of a σ-alkynyl-containing ruthenium(II) complex Ru(O₂CR²)(CCPh)(CO)(PPh₃)₂ (R²=CHCHCHCHCH₃), the molecular structure of which was established by X-ray diffraction. This σ-alkynyl complex then reacts with phenylacetylene to form a σ-butenynyl-containing compound Ru(O₂CR²)(C(CCPh)CPhH)(CO)(PPh₃)₂ (R²=CHCHCHCHCH₃). Both reactions support the key role of alkynyl ligands in the dimerization of alkynes.     

Anti-Mycobacterium tuberculosis activity of platinum(II)/N,N-disubstituted-N′-acyl thiourea complexes

Synthesis, characterization and anti-Mycobacterium tuberculosis assays of new platinum(II)/dppf/N,N-disubstituted-N′-acyl thiourea complexes with general formulae [Pt(dppf)(L)]PF₆, [dppf = 1,1′-bis(diphenylphosphino)ferrocene; L = N,N-disubstituted-N′-acyl thioureas] is reported. The complexes were characterized by elemental analysis, molar conductivity, IR, NMR (¹H, ¹³C and ³¹P{¹H}) spectroscopy. The spectroscopic data are consistent with the complexes containing one dppf and one O, S chelated ligand. The crystal structures of complexes with N,N-diphenyl-N′-benzoylthiourea (L4), N,N-diethyl-N′-furoylthiourea (L5) and N,N-diphenyl-N′-(thiophene-2-carbonyl)thiourea (L8) were determined by X-ray crystallography, confirming the coordination of the ligands with the metal through sulfur and oxygen atoms, forming distorted square-planar structures. The complexes were screened with respect to their anti-M. tuberculosis activity (H37Rv ATCC 27294).     

Kinetics of the metal exchange reaction of a Cu(II)-poly(vinyl alcohol) complex with Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid in aqueous solution

The kinetics of the metal exchange reaction between Cu(II)-poly(vinyl alcohol) [Cu(II)-PVA] and Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid [Zn(II)-EDTA] has been studied by mixing both solutions in a spectrophotometer at pH 10.0 to 11.0, ionic strength μ=0.10(KNO₃), and 15 to 35°C. The reaction is initiated by the formation of unstable Cu(II)-H-PVA through attack of H⁺ ion on the Cu(II)-PVA complex, and both reactions, ligand exchange and metal exchange, proceed simultaneously. The metal exchange step may be rate determining. The rate equation and rate constants of this reaction were determined as follows: ?d[Cu(II)-PVA]/dt=k _0(H)[PVA^?][Cu(II)-PVA] [Zn(II)-EDTA], wherek _0(H)=k ₁+(k′₂+k′₃)[H⁺],k ₁=5.98±1.64M ^?1 s^?1, andk ₂+k ₃=k′₂ K _Cu(II)-H-PVA ^?H +k′₃ K _Zn(II)-EDTA ^H =(5.91±0.89)×10⁷ M ^?2 s^?1.     

Bis(di-2-pyridyl ketoximate-O,N,N′)bis(di-2-pyridyl ketoxime-N,N′)dicopper(II) diperchlorate: A plausible,weakly ferromagnetically-coupled intermediate in the formation of the neutral,strongly antiferromagnetically-coupled neutral dimer bearing only deprotonated ligands

Complex [Cu₂{(py)₂CNO}₂{(py)₂CNOH}₂](ClO₄)₂ (2) has been isolated and proven to be an intermediate of the reaction that leads to the known, neutral dimer [Cu₂{(py)₂CNO}₄]·2H₂O (1), where (py)₂CNOH = di-2-pyridyl ketoxime; the different topologies of the double oximato bridge in the two complexes lead to different magnetic responses.     

Studies on the use of N,N,N′,N′-Tetra(2-Ethylhexyl) Diglycolamide (TEHDGA) for Actinide Partitioning II: Investigation on Radiolytic Stability

Abstract

N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (TEHDGA) was found to be a promising extractant for actinide partitioning from high-level waste (HLW) (Part I). In order to evaluate the applicability of TEHDGA to the HLW partitioning process, investigations on its radiolytic stability were carried out. The present work deals with the studies on the uptake of americium by γ-irradiated 0.2 M TEHDGA/n-dodecane in the absence and presence of phase modifiers—di(n-hexyl)octanamide (DHOA), isodecanol and n-decanol—against the absorbed dose up to 1 × 10⁶ Gy in the presence of nitric acid at varying concentrations. The addition of phase modifiers suppressed the radiolysis of TEHDGA in n-dodecane and DHOA was found to be the most effective radiolysis suppressor. Investigations were also carried out on the degradation of neat TEHDGA by γ-irradiation, and it was attempted to isolate and identify its degradation products by instrumental analysis. The radiolysis study showed that the degradation products were formed by the cleavage of the –C-N bond, to eliminate an ethylhexyl group, and the bond adjacent to the ether bond. The results obtained for TEHDGA radiolysis were compared with that of its straight-chain isomer TODGA, and TEHDGA was observed to be more resistant to radiation than TODGA. The changes in the physico-chemical properties of γ-irradiated TEHDGA against the absorbed dose were also investigated.     

Ru(II)–CO complexes of thioarylazoimidazoles: Syntheses,structures, spectroscopy and DFT calculation

The complexes, cis-(CO)-trans-(Cl)-[Ru(SRaaiNR)(CO)₂Cl₂] (2) and trans-(Cl)-[Ru(SRaaiNR)(CO)Cl₂] (3) (SRaaiNR = 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazoles; R = Me (1a) and Et (1b)) have been synthesized and characterized. The structural confirmation is achieved by single crystal X-ray structure determinations. The complexes show Ru(III)/Ru(II) couple and ligand reductions. Electronic structure and spectral properties of the complexes have been explained with the DFT and TDDFT calculation.     

Synthesis and characterization of iron(II) and iron(III) complexes with a tridentate O,N,O′-ligand

The coordination chemistry of the ligand precursor 1-benzoyl-4,5-dihydro-3,5-bis(trifluoromethyl)-1H-pyrazol-5-ol (1a) to iron(II) acetate was studied. In dependence of the added co-ligand different complex geometries were observed. In case of 4-dimethylaminopyridine (DMAP) as co-ligand an octahedral iron(II) complex was found with an O,N,O′-coordination of the tridentate ligand (1a-2H), in which the ligand is planar, the oxygen donors are trans to each other, and the nitrogen donor is in a cis position. The other coordination sites on the iron center are occupied by DMAP ligands. In contrast to that, with triphenylphosphane as the co-ligand an oxidation process took place, which revealed an octahedral iron(III) complex with a comparable geometry for the tridentate ligand (O,N,O′-coordination, 1a-2H) demonstrating the usefulness of 1a-2H to stabilize different oxidation states. The additional coordination sites are occupied by one triphenylphosphane oxide and ethoxide ligands. Interestingly, the ethoxide ligands act as bridging ligands to form a bimetallic complex.     

Kinetics of the metal exchange reaction of a Cu(II)-poly(vinyl alcohol) complex with Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid in aqueous solution

The kinetics of the metal exchange reaction between Cu(II)-poly(vinyl alcohol) [Cu(II)-PVA] and Zn(II)-ethylenediamine-N,N,N,N-tetraacetic acid [Zn(II)-EDTA] has been studied by mixing both solutions in a spectrophotometer at pH 10.0 to 11.0, ionic strength =0.10(KNO₃), and 15 to 35°C. The reaction is initiated by the formation of unstable Cu(II)-H-PVA through attack of H⁺ ion on the Cu(II)-PVA complex, and both reactions, ligand exchange and metal exchange, proceed simultaneously. The metal exchange step may be rate determining. The rate equation and rate constants of this reaction were determined as follows: –d[Cu(II)-PVA]/dt=k _0(H)[PVA^–][Cu(II)-PVA] [Zn(II)-EDTA], wherek _0(H)=k ₁+(k₂+k₃)[H⁺],k ₁=5.98±1.64M ^–1 s^–1, andk ₂+k ₃=k₂ K _Cu(II)-H-PVA ^–H +k₃ K _Zn(II)-EDTA ^H =(5.91±0.89)×10⁷ M ^–2 s^–1.     

Sulfate binding in zinc(II) complexes of a monopyridylurea ligand N-(1-naphthyl)-N′-(3-pyridyl)urea

Two zinc(II) complexes of a urea-functionalized pyridyl ligand, [Zn(SO₄)L₃]·CH₃OH (1) and {[Zn(μ₂-SO₄)L₂]·0.5CH₃OH}_n (2) (L = N-(1-naphthyl)-N′-(3-pyridyl)urea), have been synthesized by the reaction of L with ZnSO₄·7H₂O under different conditions. Complex 1 is a hydrogen-bonded 2D grid structure in which the sulfate anion not only coordinates to the Zn^II ion as a monodentate ligand but also forms multiple hydrogen bonds with the urea groups of adjacent molecules. In complex 2 the sulfate ion serves as a μ₂-bridging ligand, connecting the Zn^II ions to form an infinite 1D organic–inorganic hybrid framework. Meanwhile, the sulfate anion is also bound by neighboring ligands through hydrogen bonds between urea groups and the non-coordinated oxygen atoms. The solid-state emission spectra of 1 and 2 show a red shift of the fluorescence emission of ligand L.     

Cationic Micelles Modulated in the Presence of α,ω-Alkanediols: A SANS,NMR and Conductometric Study

The solution behavior of a typical cationic surfactant, tetradecyltrimethylammonium bromide, in mixed solvent systems composed of water and varying concentrations of α,ω-alkanediols; 1,2-ethanediol (ED), 1,4-butanediol (BD), 1,6-hexanediol (HD) and 1,8-octanediol (OD) was examined via electrical conductance measurements, ¹³C-NMR spectroscopy and small angle neutron scattering (SANS) measurements. The critical micelle concentration (CMC) values and degree of counterion dissociation (α) indicate that both ED and BD oppose micellization, whereas HD and OD enhance micelle formation. Changes in the ¹³C-NMR chemical shifts (∆δ values) reveal that the short chain diols reside almost exclusively in the bulk phase and hence, affect the formation of micelles by altering the solvent properties in the bulk of the solution, whereas HD and OD partition between the pseudomicellar phase and the bulk phase. SANS studies indicated that both the micellar size and aggregation number (N _agg) decrease in the presence of all diols. ED and BD behave like cosolvents and increase the α and CMC values and decrease N _agg. We note that the effect of HD and OD on the properties of the micelles is concentration dependent; at low concentrations, these diols interact with the micelles and behave as cosurfactants (as evidenced by the trends in the micellar properties), while at higher concentrations, they enhance the surfactant solubility and behave as a cosolvent.     

Copolymerization of ethene with norbornene using palladium(II) α-diimine catalysts: Influence of feed composition, polymerization temperature, and ligand structure on copolymer properties and microstructure

Four cationic palladium(II) α-diimine complexes, [{ArNC(R)-C(R)NAr}Pd(Me)(CH₃CN)] (1, R=H, Ar=2,6-Me₂C₆H₃, =B[3,5-C₆H₃(CF₃)₂]₄; 2, R=CH₃, Ar=2,6-iPr₂C₆H₃; 3, R=CH₃, Ar=2-tBuC₆H₄; 4, R,R=An, Ar=2,6-iPr₂C₆H₃) were used for the copolymerization of ethene with norbornene. The copolymerization behavior of the catalysts and the influence of the polymerization temperature were investigated. The copolymers were characterized using ¹³C NMR spectroscopy, differential scanning calorimetry, and gel permeation chromatography techniques. Sterically demanding ortho -N-aryl substituents and rigid bulky bridge units increase the copolymer molar masses, while the incorporation level of norbornene is decreased. Microstructures with isolated norbornene units and alternating sequences are predominant. Less bulky substituted catalysts yield copolymers with higher norbornene contents and lower molar masses. Norbornene diblock sequences are dominant which are exclusively racemic connected, indicating that the insertion proceeds under chain end control. Optimal polymerization results are achieved at temperatures between 10 and 30 °C, while temperatures below 0 °C result in lower polymerization rates and molar masses. Above 30 °C, activities, molar masses, and norbornene incorporation decreases due to catalyst decomposition.     

1-D networks formed by metal⋯sulfur van der Walls contacts: Novel tetrazole–thiolato Pd(II) and Pt(II) complexes

Pd(II)– and Pt(II)–azido complexes, [M(N₃)(PMe₃)₂(C–L)] {LH = 2-(2′)-thienyl pyridine; M = Pd (1), Pt(2)}, which contain σ-bonded heterocycles (L), were treated with aryl isothiocyanate (Me₂C₆H₃–NCS) to afford the corresponding Pd(II) and Pt(II) tetrazole–thiolato complexes, trans-{M[SCN₄(2,6-Me₂C₆H₃)](PMe₃)₂(C–L)} {M = Pd (3), Pt (4)}. Complexes 3 and 4 have a 1-D helical network formed by the intermolecular M?S van der Waals contacts.     

Cationic polymerization of styrene by the TiCl4/N,N,N′,N′-tetramethylethylenediamine(TMEDA) catalyst system in benzotrifluoride,an environmentally benign solvent,at room temperature

Highly efficient carbocationic polymerization of styrene was achieved under environmentally advantageous conditions in benzotrifluoride, BTF (α,α,α-trifluorotoluene, TFT), an environmentally benign solvent at room temperature, that is without any energy consumption for cooling or heating, with even better yields than that in the usually applied volatile and harmful, widely used chlorinated solvent, dichloromethane (DCM). The polymerization was initiated by 1-phenylethyl chloride in conjunction with the TiCl₄/TMEDA (N,N,N′,N′-tetramethylethylenediamine) catalyst (coinitiator) system. Within a very short reaction time (5 min), higher conversion values were obtained in BTF (89%) than in DCM (76%), that is the TiCl₄/TMEDA combination proved to be a powerful catalyst for the carbocationic polymerization of styrene even in BTF. The molecular weight distributions of the synthesized polymers were relatively narrow in both solvents (M_w/M_n = 1.29–1.65). The effect of the increasing reaction temperature (up to room temperature) was also investigated. With increasing reaction temperature, the polydispersity decreased and M_n close to the theoretical one was obtained in BTF at room temperature. Structural analysis with ¹H NMR revealed that the major chain breaking reaction in this polymerization is indanyl ring formation between the penultimate monomer unit and the propagating carbocation. These results indicate that BTF can be utilized as a unique, inert, non-volatile, environment friendly solvent with medium polarity for cationic polymerization of styrene, a nonfluorous monomer, and based on these results, presumably it may be also applied effectively as a quite universal solvent for a large array of various polymerizations and copolymerizations for not only fluorinated, but also for nonflourous monomers, and other chemical reactions as well.     

Effect of Alkanediyl-α,ω-Type Cationic Dimeric (Gemini) Surfactants on the Reaction Rate of Ninhydrin with [Cu(II)-Gly-Tyr]+ Complex

The effect of gemini (16‐s‐16, s = 4, 5, 6) surfactants on the reaction rate of ninhydrin with [Cu(II)‐Gly‐Tyr]⁺ complex was determined using a spectrophotometric technique. The ninhydrin concentration was kept in excess in order to maintain pseudo‐first‐order conditions. The reaction followed irreversible first‐ and fractional‐order kinetics with respect to [Cu(II)‐Gly‐Tyr]⁺ and [ninhydrin], respectively. It is found that gemini surfactants effectively catalyze the reaction. The rate constants (k_ψ) first increase and then become relatively constant with increasing gemini surfactant concentration similar to conventional cetyltrimethylammonium bromide. At higher gemini surfactant concentration a third region of increasing k_ψ is observed. The unusual third region is ascribed to changes in micellar morphology. The kinetic data has been analyzed using a micellar pseudo‐phase model.