Zinc(II) mediated synthesis of an N-substituted 2-(2-pyridyl)imidazole from a 1,2-diketone and 2-(aminomethyl)pyridine and its ligational behaviour

Reaction of anhydrous ZnCl2 with the 1:2 condensate (L) of benzil and 2-(aminomethyl)pyridine in methanol gives monomeric ZnL'Cl-2 (1) where L' is 2-[(4,5-diphenyl-2-pyridin-2-yl-1H-imidazol-1-yl)-methyl]pyridine. In the X-ray crystal structure, 1 is found to contain tetrahedral zinc with an N2Cl2 coordination sphere and the N-substituent methylpyridine fragment hanging as a free arm. A tentative mechanism is proposed for the zinc mediated conversion of L-->L'. Demetallation of 1 by the action of aqueous NaOH yields L' in the free state. When L' is reacted with Zn(ClO4)(2).6H(2)O in a 1:2 molar proportion, [Zn(L')(2)](n)(ClO4)(2n).(H2O)(n/2).(CH2Cl2)(n/2) (2) is obtained. The zinc atom in 2, as revealed by X-ray crystallography, has a trigonal bipyramidal N-5 coordination sphere. There are two independent ligands in the asymmetric unit of 2. One of them bonds only to one zinc atom in a bidentate mode with the N-substituent methylpyridine hanging free while the other ligand binds to two different zinc atoms in a tridentate fashion, employing the N-substituent methylpyridine nitrogen atom to form the polymeric one-dimensional chain cation.

3-and 3,4-substituted pyrroles and thiophenes and their corresponding polymers: a review

In the field of conducting polymers, both poly(pyrrole) and poly(thiophene) have been investigated extensively and are used currently in a wide variety of applications including microelectronics, electrode materials, sensors and optoelectronics. Amongst these polymers, 3- and 3,4- substituted poly(pyrroles) and poly(thiophenes) have received significant attention in recent years as demonstrated by the increase in the number of patents and publications that describe their use. This review covers the development in the synthesis of 3- and 3,4- Substituted poly(pyrroles) and poly(thiophenes) over the last 30 years, their polymerisation in addition to describing the material properties and applications of the resulting polymers. In particular, this review focuses upon the variety of methodologies employed for the synthesis of 3- and 3,4-substituted pyrroles and thiophenes as well as upon the broad range of functional groups that can be attached to the heterocyclic ring system in order to tailor the properties of the resulting polymers.

Bis- and tris-(3-aminopropyl) derivatives of 14-membered tetraazamacrocycles containing pyridine: synthesis, protonation and complexation studies

New N-(3-aminopropyl) (L-1, L-2) and (2-cyanoethyl) (L-3, L-4) derivatives of a 14-membered tetraazamacrocycle containing pyridine have been synthesized. The protonation constants of L-1 and L-2 and the stability constants of their complexes with Ni2+, Cu2+, Zn2+ and Cd2+ metal ions were determined in aqueous solutions by potentiometry, at 298.2 K and ionic strength 0.10 mol dm(-3) in KNO3. Both compounds have high overall basicity due to the presence of the aminopropyl arms. Their copper(II) complexes exhibit very high stability constants, which sharply decrease for the complexes of the other studied metal ions, as usually happens with polyamine ligands. Mono- and dinuclear complexes are formed with L-2 as well as with L-1, but the latter exhibits mononuclear complexes with slightly higher K-ML values while the dinuclear complexes of L-2 are thermodynamically more stable. The presence of these species in solution was supported by UV-VIS-NIR and EPR spectroscopic data. The single crystal structures of [Cu(H2L2)(ClO4)](3+) and [(CoLCl)-Cl-3](+) revealed that the metal centres are surrounded by the four nitrogen atoms of the macrocycle and one monodentate ligand, adopting distorted square pyramidal geometries. In the [(CoLCl)-Cl-3](+) complex, the macrocycle adopts a folded arrangement with the nitrogen atom opposite to the pyridine at the axial position while in the [Cu(H2L2)(ClO4)](3+) complex, the macrocycle adopts a planar conformation with the three aminopropyl arms located at the same side of the macrocyclic plane.

New bis(triazinyl) pyridines for selective extraction of americium(III)

New hydrophobic, tridentate nitrogen heterocyclic reagents (BATPs) such as 2,6-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo[1,2,4]triazin-3-yl) pyridine (1) and 2,6-bis(9,9,10,10-tetramethyl-9,10-dihydro-1,2,4-triaza-anthrane-3-yl) pyridine (2) have been studied. I is resistant to hydrolysis in 3 M nitric acid, whereas 2 is resistant to both acid hydrolysis and radiolysis. The molecules are able to give significantly enhanced separations of americium(III) from an excess of europium(III) in nitric acid. Typically, for 1 D-Am = 500 and SFAm,/Eu = 5000 compared with D-Am = 30 and SFAm /Eu = 400 with the reference molecule 2,6-bis(isopropyl[1,2,4]triazin-3-yl) pyridine (7). In order to increase the stability of 1 and 2, the labile alpha-benzylic hydrogens that are present in 7 have been replaced by alkyl groups. Three molecules of 1 are able to enclose completely the coordination sphere of the M(III) in the crystal structure of [Y(1)(3)][Y(NO3)(5)]center dot NO3 center dot 2.5H(2)O.

The coordination chemistry of 1,2,4-triazinyl bipyridines with lanthanide(III) elements - implications for the partitioning of americium(III)

It has been established that 6-(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2'-bipyridines (R,hemi-BTPs) have properties which are intermediate between those of the terpyridines and the bis(1,2,4-triazin-3-yl)pyridines (BTPs). However, they resemble the terpyridines much more closely than the BTPs. It has been shown that Et, hemi-BTP when dissolved in TPH-a dodecane-like solvent-is a selective reagent for the separation of americium(III) from europium(III). Solution NMR in acetonitrile largely confirmed the crystallographic results. There was no evidence for a 1 : 3 complex cation, or for significant differences between metal(III)-N distances for the pyridine and 1,2,4-triazine rings. Intramolecular hydrogen bonding plays a crucial role in the formation of metal coordination spheres, which explains the differences between the terpyridyl, R,hemi-BTPs and the BTPs. Protonation of the R,hemi-BTPs facilitates a conformational change which is necessary for complexation.

The trapping and decomposition of toxic gases such as hydrogen cyanide using modified mesoporous silicates

Selected silicas were modified with the covalently bound ligand 2,6-bis(benzoxazoyl)pyridine (BBOP), equilibrated with copper(II) nitrate, then challenged with toxic vapour containing HCN (8000 mg m(-3) at 80% relative humidity). The modified SBA-15 material (Cu-BBOP-SBA-15) had an improved breakthrough time for HCN (36 min at a flow rate of 30 cm(3) min(-1)) when compared to the other siliceous materials prepared in this study, equating to a hydrogen cyanide capacity of 58 mg g(-1), which is close to a reference activated carbon adsorbent (24 min at 50 cm(3) min(-1)) that can trap 64 mg g(-1). The enhanced performance observed with Cu-BBOP-SBA-15 has been related to the greater accessibility of the functional groups, arising from the ordered nature of the interconnected porous network and large mesopores of 5.5 nm within the material modified with the Cu(II)-BBOP complex. Modified MCM-41 and MCM-48 materials (Cu-BBOP-MCM-41 and Cu-BBOP-MCM-48) were found to have lower hydrogen cyanide capacities (38 and 32 mg g(-1) respectively) than the Cu-BBOP-SBA-15 material owing to the restricted size of the pores (2.2 and <2 nm respectively). The materials with poor nano-structured ordering were found to have low hydrogen cyanide capacities, between 11 and 19 mg g(-1), most likely owing to limited accessibility of the functional groups. (C) 2004 Elsevier Inc. All rights reserved.

A study of co-precipitated bimetallic gold catalysts for water-gas shift reaction

Synthesis, testing and characterisation of bimetallic gold, Au-M on ceria as catalysts were carried out for low temperature water-gas shift reaction (WGS). Amongst the entire screened catalysts 3 wt% (AU-Pt)/CeO2 displayed the best WGS activity than the monometallic promotors, giving the light-off curve at the lowest temperature in the range 100-300 degrees C. (Au-Pd)/CeO2 also achieved the same activity but at a higher temperature. It was also found that WGS activity was strongly correlated with the surface reducibility which in turn depended on the modified local electronic band structure of promoted ceria. These results clearly suggest that the key role of bimetallic promoter may involve in facilitating the creation of defective reduced surface by exerting its local electronic effect on ceria to form the surface germinal -OH groups in water which act as active sites for enhanced WGS activity. (C) 2008 Elsevier B.V. All rights reserved.

Exploring the applications of a pulsating jet hydrodynamic modulated voltammetric (HMV) system - electrochemistry of nanostructured Pt electrodes and trace analysis

The electrochemistry of nanostructured electrodes is investigated using hydrodynamic modulated voltammetry (HMV). Here a liquid crystal templating process is used to produce a platinum modified electrode with a relatively high surface area (Roughness factor, Rf = 42.4). The electroreduction of molecular oxygen at a nanostructured platinum surface is used to demonstrate the ability of HMV to discriminate between Faradaic and non-Faradaic electrode reactions. The HMV approach shows that the reduction of molecular oxygen shows considerable hysteresis correlating with the formation and stripping of oxide species at the platinum surface. Without the HMV analysis it is difficult to discern the same detail under the conditions employed. In addition the detection limit of the apparatus is explored and shown, under ideal conditions, to be of the order of 45 nmol dm(-3) employing [Fe(CN)(6)](4-) as a test species. (C) 2009 Elsevier B.V. All rights reserved.

Oxovanadium(V) complexes of bis(phenolate) ligands with acetylacetone as co-ligand: synthesis, crystal structure, electrochemical and kinetics studies on the oxidation of ascorbic acid

Two vanadium(V) complexes, [VO(L-1)]acac)] (1) and [VO(L-2)(acac)] (2), where H2L1 = N,N-bis(2-hydroxy-3-5-di-tert-butyl-benzyl)propylamine and H2L2 = 2,2'-selenobis(4,6-di-tert-butylphenol), have been synthesized and characterized by elemental analyses, IR, V-51 NMR, both in the solid and in solution, and cyclic voltammetric studies. Single crystal X-ray studies reveal that in complex 1 the vanadium atom is octahedrally coordinated with an O5N donor environment, where the oxygen atom of the V-V=O moiety and the N atom of the ONO ligand occupy the axial sites while two oxygen atoms (O1 and O2) from the bisphenolate ligand and two oxygen atoms (O3 and O4) from the acac ligand occupy the equatorial plane. A similar bonding pattern has also been encountered for 2 with the exception that a Se atom instead of N is involved in weak bonding to the metal center. Both complexes showed reversible cyclic voltammeric responses and E-1/2 appears at -0.18 and 0.10 V versus NHE for complexes 1 and 2, respectively. The kinetics of oxidation of ascorbic acid by complex 1 were carried out in 50% MeCN-50% HO (v/v) at 25 degrees C. The high formation constant value, Q = 63 +/- 7 M-1, reveals that the reaction proceeds through the rapid formation of a H-bonded intermediate. The low k(2)Q(2)/k(1)Q(1) ratio (13.4) for 1 points out that there is extensive H-bonding between the oxygen atom of the V-V=O group and the OH group of ascorbic acid. (c) 2007 Published by Elsevier Ltd.

Introduction of vinyl and hydroxymethyl functionalities at C-4 of glucose-derived substrates: synthesis of spirocyclic, bicyclic, and tricyclic nucleosides

Installing hydroxymethyl and hydroxyethyl substitutions at C-4 through vinylation and hydroboration-oxidation reactions of the C-4 bis-hydroxymethyl derivative of D-glucose based substrate, and inserting heteroatoms thereafter permitted formation of N-, O-, or S-heterocycles leading to [4,5]or [5,5]-spirocycles and a bicyclo[3.3.0]octane product. Some of the spirocycles were converted to spironucleosides under Vorbruggen glycosidation reaction conditions. Similarly, the bicyclic product was elaborated to the corresponding bicyclic nucleoside as well as an unexpected tricyclic nucleoside.

Tuning of intramolecular electron transfer between Ru(II) and the disulfide bond

Reaction of 2,2'-dithiodipyridine (DTDP) with cis-Ru(bpy)(2)Cl-2 (bpy = 2,2'-bipyridine) and cis-Ru(phen)(2)Cl-2 (phen = 1,10-phenanthroline) respectively yields the dicationic species [Ru(bpy) (2)(DTDP)](2+) and [Ru(phen)(2) (DTDP)](2+) in which the S-S bond of DTDP remains intact. The S-S bond undergoes a reductive cleavage when DTDP is reacted with cis-Ru(bisox)(2)Cl-2 (bisox = 4,4,4',4'-tetramethyl-2,2'-bisoxazoline) under identical conditions to generate the monocationic species [Ru(bisox)(2)(2-thiolatopyridine)]. The intramolecular electron transfer between the metal and the S-S bond is found to be subtly controlled by the crystal field strength of the ancillary bidentate N-donor ligands.

Nitrogen donor ligands bearing N-H groups: Effect on catalytic and cytotoxic activity of molybdenum eta(3)-allyldicarbonyl complexes

Reactions of [Mo(eta(3)-C3H5)Br(CO)(2)(NCMe)(2)] with the bidentate nitrogen ligands 2-(2'-pyridyl)imidazole (L1), 2-(2'-pyridyl)benzimidazole (L2), N,N'-bis(2'-pyridinecarboxamido)-1,2-ethane (L3), and 2,2'-bisimidazole (L4) led to the new complexes [Mo(eta(3)-C3H5)Br(CO)(2)(L)] (L = L1, 1; L2, 2; L4, 4) and [{Mo(eta(3)-C3H5) Br(CO)(2)}(2)(mu-L-3)] (3). The reaction of complexes 2 and 3 with Tl[CF3SO3] afforded [Mo(eta(3)-C3H5)(CF3SO3)(CO)(2)(L2)] (2T) and [{Mo(eta(3)-C3H5)(CF3SO3)(CO)(2)}(2)(mu-L-3)] (3T). Complexes 3 and 2T were structurally characterized by single crystal X-ray diffraction, showing the facial allyl/carbonyls arrangement and the formation of the axial isomer. In 2T, two molecules are assembled in a hydrogen bond dimer. The four complexes 1-4 were tested as precursors in the catalytic epoxidation of cyclooctene and styrene, in the presence of t-butylhydroperoxide (TBHP), with moderate conversions and turnover frequencies for complexes 1-3 and very low ones for 4. The increasing number of N-H groups in the complexes seems to be responsible for the loss of catalytic activity, compared with other related systems. The cytotoxic activities of all the complexes were evaluated against HeLa cells. The results showed that compounds 1,2,4, and 2T exhibited significant activity, complexes 2 and 2T being particularly promising. (C) 2008 Elsevier B.V. All rights reserved.

Preparation and ring-opening reactions of N,O-bis(diphenylphosphinyl) hydroxymethylaziridine ('Di-Dpp')

N,O-bis(diphenylphosphinyl)-2-(hydroxymethyl)aziridine ('DiDpp', 1) is efficiently prepared from 2-aminoethane-1,3-diol: this activated aziridine undergoes two sequential reactions with copper(I)-modified Grignard reagents, yielding alpha-branched N-Dpp amines in good yield. (C) 2003 Elsevier Science Ltd. All rights reserved.

Ligand-centred reactivity of bis(picolyl)amine iridium: sequential deprotonation, oxidation and oxygenation of a "non-innocent" ligand

Treatment of [Ir(bpa)(cod)](+) complex [1](+) with a strong base (e.g., tBuO(-)) led to unexpected double deprotonation to form the anionic [Ir-(bpa-2H)(cod)](-) species [3](-), via the mono-deprotonated neutral amido complex [Ir(bpa-H)(cod)] as an isolable intermediate. A certain degree of aromaticity of the obtained metal-chelate ring may explain the favourable double deprotonation. The rhodium analogue [4](-) was prepared in situ. The new species [M(bpa-2H)(cod)](-) (M = Rh, Ir) are best described as two-electron reduced analogues of the cationic imine complexes [M-I(cod)(Py-CH2-N=CH-Py)](+). One-electron oxidation of [3](-) and [4](-) produced the ligand radical complexes [3]* and [4]*. Oxygenation of [3](-) with O-2 gave the neutral carboxamido complex [Ir(cod)(py-CH2-N-CO-py)] via the ligand radical complex [3]* as a detectable intermediate.

Transition metal-directed self-assembly of calix[4]arene based dithiocarbamate ligands

The transition metal-directed self-assembly of dithiocarbamate ligand functionalised upper and lower rim calix[4]arenes affords novel dimeric bimetallic bis(calix[4]arene) species as determined by a combination of analytical methods including X-ray crystallography. An exception is a zinc(II) dithiocarbamate upper rim calix[4]arene assembly which is monomeric in nature. Electrochemical investigations reveal the bimetallic copper(II) bis(calix[4]arene) systems can electrochemically sense dihydrogen phosphate and carboxylate anions via significant cathodic perturbations of the respective copper(II)/(III) dithiocarbamate oxidation wave.