Enantioselective catalysis of Claisen rearrangement by DABNTf-Pd(II) complex

Two types of palladium complexes, cationic and neutral (R)-DABNTf-Pd(CH₃CN)₂ were examined as chiral catalysts for enantioselective Claisen rearrangement. DABNTf-Pd(CH₃CN)₂ complex gave high enantio- and anti-diastereoselectivity, and good yield. This Claisen rearrangement should proceed via six-membered boat transition state through bi-dentate coordination to the Pd catalyst.     

Palladium complexes with meso-bioxazoline ligands for alternating styrene/CO copolymerisation: Counterion effect

Two sets of mono- and dicationic palladium complexes (8) and (10), having and as counterions, were synthesised. The interionic structure of the methyl-acetonitrile complexes [Pd((R,S)-Bn-Box)(CH₃)(NCCH₃)](X) (8) in solution, was investigated by pulsed-gradient spin-echo (PGSE) diffusion measurements and (¹H, ¹⁹F)-HOESY NMR spectroscopy. A high degree of ion-pairing was found in each complex. The HOESY spectra showed that the and anions take up selective positions, on the side of the complex remote from the benzyl groups, but close to the acetonitrile ligand, while the triflate is, partially, occupying a pseudo fifth coordination position on the side of the cation remote from the two benzyl-groups. The complexes 8 and 10 were used as catalyst precursors for the copolymerisation of styrene with carbon monoxide, producing syndiotactic copolymers, with the exception of complex 10a, that led to isotactic copolymers.     

Compositional variations in monomeric trimethylsilylated allyl lanthanide complexes

Treatment of three equivalents of the potassium salt of the bis(1,3-trimethylsilyl)allyl anion with various late lanthanide triflates (M = Dy, Ho, Er, Tm, Lu) produces the unsolvated triallyllanthanide complexes (A′ = 1,3-(SiMe₃)₂C₃H₃). The use of lanthanide halides (Cl, I) with the potassium allyl also generates neutral complexes, but when lanthanide iodides and the corresponding lithium allyl are combined, the lanthanate species are formed. Trends in the bonding of lanthanide allyl complexes with the trimethylsilylated-allyl ligand are explored and compared with those of cyclopentadienyl lanthanide complexes.     

Cationic η-allyl sulfide complexes of nickel(II) for the polymerization of butadiene in aqueous emulsion

Reaction of the dimeric allyl-nickel(II) chloro complex [Ni(η³-C₃H₅)(μ-Cl)]₂ (5) with sulfur donor ligands (L = L₁₀-L₁₃) in the presence of ( = 3,5-(CF₃)₂C₆H₃) gives the corresponding cationic mononuclear complexes of the type [Ni(η³-C₃H₅)(L)₂]⁺ (1-4) [L = L₁₀ = diphenyl sulfide (1); L = L₁₁ = 4,4′-thiodiphenol (2); L = L₁₂ = 4,4′-thio-bis(6-tert-butyl-o-cresol) (3); L = L₁₃ = 4,4′-thio-bis (6-tert-butyl-m-cresol) (4)]. All of these complexes were characterized by elemental analysis and NMR spectroscopy, as well as the representative complex 3 additionally by single-crystal X-ray analysis. In comparison to the known complex [Ni(η³-C₃H₅)(η⁶-BHT)][B] (BHT = 3,5-di-tert-butyl-4-hydroxytoluene), the herein described cationic complexes show an increased stability towards water. The activity of the complexes for butadiene polymerization in aqueous emulsions was studied.     

Pyrazolyl-pyrimidine based ligands in palladium catalyzed copolymerization and terpolymerization of CO/olefins

Cationic palladium(II) complexes of the type containing bisnitrogen ligands with a pyrazole moiety were synthesized from the corresponding neutral derivatives [PdClMe(N-N′)]. Their characterization by ¹H and ¹³C NMR spectroscopy in solution evidences the presence of the Pd-Me group cis to the pyrazole ring. The catalytic behaviour of the cationic complexes in CO/4-tert-butylstyrene copolymerization and CO/ethylene/4-tert-butylstyrene terpolymerization was investigated. Productivity was greatly enhanced when the reaction was carried out in 2,2,2-trifluoroethanol (TFE). Molecular weights and polydispersity (M_w/M_n) of the obtained polyketones resulted among the best reported for C_s-bisnitrogen planar ligands.     

Deprotonated diindolylmethanes as dianionic analogues of scorpionate bis(pyrazolyl)borate ligands: synthesis and structural characterization of representative titanocene and zirconocene complexes

Deprotonation of di(3-methylindol-2-yl)phenylmethane (L₂H₂) or with two equivalents of ⁿBuLi, followed by reactions with Cp₂TiCl₂ or Cp₂ZrCl₂ yielded complexes . Compounds 1-4 were characterized by NMR spectroscopy, and compounds 1, 3, and 4 were further analyzed by X-ray crystallography and elemental analysis. The molecular structures of 1, 3, and 4 illustrate that chelating di(3-methylindol-2-yl)methanes have a structural relationship to coordinated bis(pyrazolyl)borates.     

Synthesis and application of novel ionic phosphine ligands with a cobaltocenium backbone

Six novel ionic phosphine ligands with a cobaltocenium backbone, 1,1′-bis(dicyclohexylphosphino) cobaltocenium hexafluorophosphate () (1a), 1,1′-bis(di-iso-propylphosphino) cobaltocenium hexafluorophosphate () (2a), 1,1′-bis(di-tert-butylphosphino) cobaltocenium hexafluorophosphate () (3a), and the monophosphine ligand (Cc⁺ = cobaltocenium; R = Cy, 1b; R = i-Pr, 2b; R = t-Bu, 3b) were synthesized and characterized by elemental analysis, spectroscopy, and X-ray diffraction techniques. These ligands are air-stable and useful for Suzuki coupling reactions in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (), enabling high catalytic activity.     

Cu(II) complex of a flexible tripodal receptor as a highly selective fluorescent probe for iodide

A Cu(II) complex of a tripodal receptor bearing an anthracene moiety on one pod as a fluorophore was synthesized. The anion recognition behavior of the Cu(II) complex was evaluated in CH₃CN/H₂O (95:5, v/v), resulting in an extremely high selectivity for iodide over other anions such as F⁻, Cl⁻, Br⁻, , CH₃COO⁻, and . The Cu(II) complex acts as a selective probe for estimating iodide even in the presence of other anions without any interference.     

Investigation of charge transfer and structural distortions during photo-inducted excitation of cuprous bis-2,9-dimethyl-1,10-phenanthroline complex by density functional theory

This work reported the investigation of the structural distortions and charge-transfer processes that occurred in the complex of cuprous(I) bis-2,9-dimethyl-1,10-phenanthroline upon oxidation to copper(II), , through a excited state of by density functional theory. The intramolecular electronic transfer from central metal-to-ligand (MLCT) upon the irradiation of light energy is confirmed. Due to this MLCT excitation, the structure of the excited state of is distorted and reorganized to adapt with the change of charge in central metal. As a result, the excited state of is formed, which has the similar electronic and structural properties with . The bulky substituents in 2- and 9-positions of the phenanthroline ligands can restrain the structural distort and decrease nonradiative decay rate. Thus, the electronic and steric effects of the ligands in the cuprous photo-sensitive complexes have important consequences in the behavior of their excited state.     

Synthesis, characterization, and the role of counterion in stabilizing trigonal pyramidal copper(I)/2,2′bipyridine complexes containing electron-poor methyl acrylate

Copper(I)/2,2′-bipyridine complexes, [Cu^I(bpy)(π-CH₂CHCOOCH₃)][A] have been synthesized and characterized. These complexes are used in copper(I) mediated cyclopropanation and aziridination reactions of methyl acrylate and represent the first class of trigonal pyramidal copper(I) complexes with π-coordinated electron poor olefins. In the case of 1 and 3, weak coordination of the counterion was observed. The counterion was noncoordinating in complex 2, which was dimeric in the solid state with the oxygen atoms of the carbonyl moieties in methyl acrylate bridging two copper(I) centers.     

Syntheses of acetonitrile ligated copper complexes with perfluoroalkoxy aluminate as counter anion and their catalytic application for olefin aziridination

Acetonitrile ligated copper complexes with perfluoroalkoxy aluminate as weakly coordinating counter anion are successfully synthesized. Aziridination of various olefins with PhINTs catalyzed by copper(II) complex [Cu(II)(NCCH₃)₆][Al{OC(CF₃)₃}₄]₂ affords good to excellent yields (up to 96%) and very high turnover frequency (higher than 5000 h⁻¹) under mild conditions.     

Synthesis of new aromatic perfluorovinyl ether monomers containing phosphonic acid functionality

The synthesis of a new perfluorovinyl ether monomer containing phosphonic acid functionality is reported. It started from 4-[(α,β,β-trifluorovinyl)oxy]bromo benzene prepared in two steps from the nucleophilic substitution of 4-bromophenate to 1,2-dibromotetrafluoroethane. The [(α,β,β-trifluorovinyl)oxy]benzene dialkyl phosphonate was prepared according to various methods of phosphonation like a Michaelis-Arbuzov or a Michaelis-Becker or a palladium catalysed arylation in the presence of various reactants. The influence of the nature of the method and of the reactants onto the yields is discussed. It was shown that reaction involving a palladium triphenyl phosphine catalyst led to the best yield. All different aromatic intermediates and fluoromonomers were characterised by , and NMR, mass spectrometry (EI), and by FTIR.