Lower-RIM Polyphosphorylated Calix[4]arenes. Their Use as Extracting Agents for Thorium (IV) and Europium (III) Ions

The extraction of thorium (IV) and europium (III) ions from aqueous nitrate media (1 M nitric acid and sodium nitrate) using six p-tert -butylcalix[4]arene derivatives bearing phosphine oxide units (--CH 2 P(O)Ph 2 ) anchored at the lower rim has been investigated at 25°;C. All ligands display higher extracting properties toward thorium than europium ions. The number and position on the lower rim of the ligating groups play a crucial role in the extraction process, the highest extraction percentages being in each case achieved with the tetra-phosphorylated calixarene. In the presence of sodium nitrate the extraction percentages are considerably higher than those obtained in the presence of nitric acid.     

Multifunctional Calix[4]arenes Containing Pendant Amide and Phosphoryl Groups: Their Use as Extracting Agents and Carriers for Alkali Cations

The complexing, extracting and mobile carrier properties of the tetra(phosphine oxide)-calix[4]arene 1 and the hybrid diamide-di(phosphine oxide)-calix[4]arene 2 were studied. Both ligands give 1 : 1 complexes with alkali cations in THF as shown by the picrate method. 1H NMR experiments were run to follow encapsulation of sodium and potassium cations. The corresponding spectra indicate C2-symmetrical structure. The observed extraction orders of the alkali picrates were as follows K+>Rb+>Li+>Cs+>Na+ for 1 and Li+>Na+>K+>Rb++ for 2. Transport kinetics was analysed by means of a model which assumes pure diffusion and which allows the evaluation of mass transfer coefficients in all systems. These coefficients and their influences on the transport rate are discussed in terms of size of the transporting species in the liquid membrane.     

Novel phosphorylated calixarenes for the recognition of f-elements

The binding properties of three series of phosphorylated calixarene derivatives bearing phosphine oxide or phosphonate groups either at the wide or the narrow rims have been investigated towards some representative lanthanide and actinide ions using several approaches: (i) liquid–liquid extraction of europium, americium, thorium and uranyl ions from nitric acid solutions into the two diluents m-nitrobenzotrifluoride (m-NBTF) or dichloromethane; (ii) complexation in single media (methanol and acetonitrile) followed by UV-spectrophotometric and isoperibolic (micro)calorimetric titrations (ITC). The latter technique was found to be very useful for the determination of the stoichiometries of the complexes formed, in particular when the complexation did not induce significant spectral changes. It also provided a full thermodynamic characterization of these new systems. The influence of some structural features of the ligands as the nature of the substituents and the condensation degree of the calixarene moiety, on the distribution coefficients and on the complexation thermodynamic parameters has been established.     

Extraction and coordination behavior of diphenyl hydrogen phosphine oxide towards actinides

Extraction behavior of some selected actinides like U(VI), Th(IV), and Am(III) was investigated with three different H-phosphine oxides, viz. diphenyl hydrogen phosphine oxide (DPhPO), dihexyl hydrogen phosphine oxide (DHePO) and diphenyl phosphite (DPP). The H-phosphine oxides exhibited a dual nature towards the extraction of actinides where the ligand not only extracts the metals by cation exchange but also by coordination with the phosphoryl group at lower and higher acidic concentrations, respectively. Among all ligands employed, DPhPO showed highest extraction with actinides with a substituent dependent trend as follows: DPhPO > DHePO > DPP. This trend emphasizes the importance of substituents around the phosphine oxide towards their extraction of actinides. The coordination behavior of DPhPO was studied by investigating its corresponding complexes with Th(NO₃)₄ and UO₂(NO₃)₂. The metal complexes of these actinides were characterized using FT-IR, ¹H and ³¹P NMR spectroscopic techniques. Density Functional Theory (DFT) calculations were also performed to understand the electronic and geometric structure of the ligand and the corresponding metal complexes.     

Markovnikov hydroformylation catalyzed by ROPAC in the presence of phosphine and phosphine oxide ligands

Rhodium-catalyzed hydroformylation of 1-octene in the presence of different phosphine and phosphine oxide ligands has been investigated. The molecular structure of new phosphine ligand, fluorenylidine methyl phenyl diphenylphosphine, was determined by single-crystal X-ray crystallography. Parameters such as different ligands, molar ratio of ligand to rhodium complex, ratio of olefin to rhodium complex, pressure of CO : H₂ mixture, and time of the reaction were studied. The linear aldehyde was the main product when the phosphine ligands were used as auxiliary ligands while the selectivity was changed to the branched products when the related phosphine oxide ligands were used. Under optimized reaction conditions, in the presence of [Rh(acac)(CO)(Ph₃P)]-di(1-naphthyl)phenyl phosphine oxide, conversion of 1-octene reached 97% with 87% selectivity of branched aldehyde.     

Platinum-catalyzed selective hydration of hindered nitriles and nitriles with acid- or base-sensitive groups

Hindered tertiary nitriles can be hydrolyzed under neutral and mild conditions to the corresponding amides using platinum(II) catalysts with dimethylphosphine oxide or other secondary phosphine oxides (SPOs, phosphinous acids) as ligands. We have found that this procedure also works well for nitriles with acid- or base-sensitive groups, which is unprecedented in terms of yield and selectivity. The catalyst loading can be as low as 0.5 mol %. Amides are isolated as the only product in high yield, and no further hydrolysis to the corresponding acids takes place. Reactions are carried out at 80 degrees C but take place even at room temperature. When enantiopure secondary phosphine oxide ligands are used in the hydrolysis of racemic nitriles, no kinetic resolution is observed, presumably due to racemization of the ligand during the reaction.     

Multiple proton ionizable calixarene derivatives with different ring sizes and complexation ability as efficient ionophores for complexation and solvent extraction of trivalent indium

The solvent extraction behavior of multiple proton ionizable p-tert-butylcalix[4]arene and [6]arene carboxylic acid derivatives towards indium has been investigated along with an acyclic monomeric analogue from weakly acidic media into chloroform. The extraction mechanism is ion exchange and carboxylic acid groups are adequate ligating sites for extraction. The cyclic structure of calixarene ligands to accommodate the potential guest species and the cooperativity effect of multifunctional groups significantly affect the complexation behavior and calixarene derivatives are found to be excellent extractants over the monomeric analogue. The composition of the extracted complex depends on the solution pH and attempts to determine the composition of the extracted complex for the extraction of indium have been stymied by complications arising from the formation of polynuclear species of indium and bridged polymeric species of calixarene carboxylic acid derivatives. One mole of calix[4]arene derivative extracts 2.5 moles of indium whereas the calix[6]arene derivative tends to extract 4.0 moles of indium. The loaded indium is back extracted with 1 mol dm(-3) hydrochloric acid solution. Though quantitative back extraction of indium was achieved from the fully loaded calix[6]arene derivative, it was only achieved up to 85% in the case of the calix[4]arene derivative.     

TRI (2-PYRIDYL) PHOSPHINE,TRI(2-PYRIDYL) PHOSPHINE OXIDE,AND TRI (2-PYRIDYL) ARSINE METAL (II) PERCHLORATE COMPLEXES

Abstract

Metal(II) perchlorate complexes with the ligands tri(2-pyridyl)phosphine, tri(2-pyridyl)phosphine oxide, and tri(2-pyridyl)arsine have the composition [M(TPX)₂] (ClO₄)₂. Coordination occurs only through the nitrogens of the pyridines. In the case of Cu(II) and tri(2-pyridyl)phosphine oxide, two isomers were obtained. One isomer contains symmetrical tridentate tri(2-pyridyl)phosphine oxide ligands while the second isomer contains an unsymmetrical ligand. The unsymmetrical tri(2-pyridyl)phosphine oxide may be a bidentate ligand or a bridging tridentate. Weak axial interaction between a pyridyl group and a second Cu(II) ion is postulated in solution and may be present in the solid state.     

Applications of Calixarenes in Polymer Synthesis

Summary: The applications of calixarenes in polymer synthesis have been reviewed. Calixarenes have been used as ligands to prepare rare earth calixarene complexes. A series of rare earth calixarene complexes have been synthesized and employed as efficient catalysts for the polymerization of ethylene, styrene, butadiene, propylene oxide, styrene oxide, trimethylene carbonate, and 5,5-dimethyl trimethylene carbonate. On the other hand, the synthesis and characterization of star-shaped polymers with calixarene as core molecules are also described.     

Liquid-liquid extraction of transition and alkali metal cations by a new calixarene: Diphenylphosphino calix[4]arene methyl ether

The liquid-liquid extraction of various metal ions by a diphenylphosphino calix[4]arene (1) using picrate counter ion has been studied and compared with those ofp-tert-butyl-calix[4]arene methyl ether (2) and triphenylphosphine (3). The calixarene 1 shows strong binding ability to almost all metal cations examined, but calixarene 2 shows little ability to extract any of them. Based on the continuous variation method, calixarene 1 formed 1: 2 complexes with copper(II) ion.     

Mono-ionizable calix[4]arene-benzocrown-6 ligands in 1,3-alternate conformations: synthesis, structure and silver(I) extraction

Two series of novel mono-ionizable calix[4]arene-benzocrown-6 ligands in 1,3-alternate conformations are synthesized. In one series, the proton-ionizable group (PIG) is attached to the para position of one aromatic ring in the calixarene framework, thereby positioning it over the polyether ring cavity. In the other series, the PIG is a substituent on the benzo group in the polyether ring. This orients the PIG away from the crown ether cavity. In addition to carboxylic acid functions, the PIGs include N-(X)sulfonyl carboxamide groups. With X group variation from methyl to phenyl to 4-nitrophenyl to trifluoromethyl, the acidity of the PIG is ‘tuned’. Solvent extraction of Ag⁺ from aqueous solutions into chloroform is used to probe the influence of structural variation within the mono-ionizable calixcrown ligand on metal ion extraction efficiency, including the identity and acidity of the PIG and its orientation with respect to the polyether ring.     

Conversion of alcohols to bromides using a fluorous phosphine

Reaction of alcohols with the fluorous phosphinecarbon tetrabromide complex in toluene or in a two-phase toluene-FC-72 system afforded the corresponding bromides in good yields. The fluorous-phosphine oxide is readily separated by liquid-liquid extraction, providing an alternative to the homogeneous triphenylphosphine-carbon tetrachloride conversion, as well as to the polymer-supported phosphine method. The fluorous phosphine oxide could be reduced and the product reused.     

2,2′-Dipyridyl-6,6′-dicarboxylic acid diamides: Synthesis,complexation and extraction properties

New ligands for complexing of the post-transition metals – diamides of 2,2′-bipyridyl-6,6′-dicarboxylic acid were developed, synthesised and characterised. They were proposed to be effective extractants towards americium. The structures of the amides were studied in solid as well as in solution. The extraction of Am and lanthanides depending on diamide structure, chlorinated cobalt dicarbollide (CCD) – diamide ratio, type of diluent was studied. The optimal conditions for Am/REE separation were determined. The properties of new potentiometric sensors on the base of 2,2′-dipyridyl-6,6′-dicarboxylic acid diamides were studied. The correlation structure vs. properties of ionophores (i.e. extractants), their sensitivity and selectivity in sensor analysis and extraction are discussed.     

Suzuki-Miyaura reaction in water, conducted by employing an amphiphilic dendritic phosphine-palladium catalyst: a positive dendritic effect on chemical yield

A series of amphiphilic dendritic ligands with a phosphine core was synthesized by use of tris(4-hydroxyphenyl)phosphine oxide and poly(benzyl ether) dendron. The corresponding phosphine-palladium core dendrimers were applied as a catalyst to an aqueous-media Suzuki-Miyaura reaction. A positive dendritic effect on chemical yields of cross-coupling products was observed.     

Novel unsymmetrical P/O substituted ferrocene ligands and the first structurally characterised hydroxyferrocene derivative

Two new unsymmetrical 1'-substituted hydroxyferrocene ligands featuring either phosphine or phosphine oxide substituents have been synthesised and the phosphine oxide derivative has been structurally characterised. A nickel complex of the hydroxyl/phosphine ligand has been formed, along with preliminary evaluation of the complex for catalysis of ethylene polymerisation.     

Copper-catalyzed asymmetric conjugate addition of diethylzinc to substituted chalcones using a chiral phosphine ligand

A series of chiral phosphine PFAM and phosphine oxide POFAM ligands were studied for the copper-catalyzed asymmetric diethylzinc addition to enones. One of these ligands, PFAM2, was an efficient catalyst with a variety of enones to give conjugate addition products in up to 96% yield and 92% ee.     

Meso-porphyrinylphosphine oxides: mono- and bidentate ligands for supramolecular chemistry and the crystal structures of monomeric {[10,20-diphenylporphyrinatonickel(II)-5,15-diyl]-bis-[P(O)Ph(2)] and polymeric self-coordinated {[10,20-diphenylporphyrinatozinc(II)-5,15-diyl]-bis-[P(O)Ph(2)]}

A series of porphyrins substituted in one or two meso positions by diphenylphosphine oxide groups has been prepared by the palladium-catalyzed reaction of diphenylphosphine or its oxide with the corresponding bromoporphyrins. Compounds {MDPP-[P(O)Ph2]n} (M = H2, Ni, Zn; H2DPP = 5,15-diphenylporphyrin; n = 1, 2) were isolated in yields of 60-95%. The reaction is believed to proceed via the conventional oxidative addition, phosphination, and reductive elimination steps, as the stoichiometric reaction of eta(1)-palladio(II) porphyrin [PdBr(H2DPP)(dppe)] (H2DPP = 5,15-diphenylporphyrin; dppe = 1,2-bis(diphenylphosphino)ethane) with diphenylphosphine oxide also results in the desired mono-porphyrinylphosphine oxide [H2DPP-P(O)Ph2]. Attempts to isolate the tertiary phosphines failed due to their extreme air-sensitivity. Variable-temperature 1H NMR studies of [H2DPP-P(O)Ph2] revealed an intrinsic lack of symmetry, while fluorescence spectroscopy showed that the phosphine oxide group does not behave as a "heavy atom" quencher. The electron-withdrawing effect of the phosphine oxide group was confirmed by voltammetry. The ligands were characterized by multinuclear NMR and UV-visible spectroscopy, as well as mass spectrometry. Single-crystal X-ray crystallography showed that the bis(phosphine oxide) nickel(II) complex {[NiDPP-[P(O)Ph2]2} is monomeric in the solid state, with a ruffled porphyrin core and the two P=O fragments on the same side of the average plane of the molecule. On the other hand, the corresponding zinc(II) complex formed infinite chains through coordination of one Ph2PO substituent to the neighboring zinc porphyrin through an almost linear P=O...Zn unit, leaving the other Ph2PO group facing into a parallel channel filled with disordered water molecules. These new phosphine oxides are attractive ligands for supramolecular porphyrin chemistry.     

Synergistic solvent extraction of Co(III) by thenoyltrifluoroacetone and some organophosphorus compounds

The extraction of Co(III) from aceticacid-acetate buffer solutions with various mixtures of ligands has been studied. Thenoyltrifluoroacetone mixed with triphenylphosphine oxide, trioctylphosphine oxide or tributyl phosphate were used as extractants. The effect of different parameters affecting the distribution ratio was studied in detail. Also, the corresponding thermodynamic parameters are calculated and discussed, together with the structures of extracted species.     

Efficient palladium-catalyzed Suzuki-Miyaura coupling of aryl chlorides with arylboronic acids using benzoferrocenyl phosphines as supporting ligands

Four monodentate benzoferrocenyl phosphines were studied as supporting ligands in palladium-catalyzed Suzuki-Miyaura coupling of aryl chlorides with arylboronic acids. Of these ligands, the more electron-rich and steric demanding benzoferrocenyl dicyclohexyl phosphine was found highly effective for the reaction followed by the benzoferrocenyl diisopropyl phosphine. The corresponding diethyl and diphenyl phosphines are much less active. When the dicyclohexyl phosphine was used, both electron-rich and electron-poor aryl chlorides were coupled with arylboronic acids within 1 h giving good to excellent yields. Chloro-substituted pyridines were also found highly reactive under these conditions giving excellent yields of biaryl products. Sterically hindered biaryls can also be prepared using the dicyclohexyl phosphine as ligand.     

Alkali metal cation complexation by 1,3-alternate,mono-ionisable calix[4]arene-benzocrown-6 compounds

Alkali metal cation extraction behaviour for two series of 1,3-alternate, mono-ionisable calix[4]arene-benzocrown-6 compounds is examined. In Series 1, the proton-ionisable group (PIG) is a substituent on the benzo group of the polyether ring that directs it away from the crown ether cavity. In Series 2, the PIG is attached to one para position in the calixarene framework, thereby positioning it over the crown ether ring. Competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform shows high Cs⁺ efficiency and selectivity. Single-species extraction pH profiles of Cs⁺ for Series 1 and 2 ligands with the same PIG are very similar. Thus, association of Cs⁺ with the calixcrown ring is more important than the position of the PIG relative to the crown ether cavity. Solid-state structures of two unionised ligands from Series 2 are presented. Also described is a crystal containing two different ionised ligand–Cs⁺ complexes.