Bromide Complexes Research Articles

Group-12 metal complexes with isomeric 1-(diphenylphosphino)-1′-[N-(pyridylmethyl)carbamoyl]ferrocenes: coordination polymers vs. finite multinuclear coordination assemblies

The isomeric ferrocene phosphine-carboxamides, 1-(diphenylphosphino)-1'-{[N-(2-pyridyl)-methyl]carbamoyl}ferrocene (1) and 1-(diphenylphosphino)-1'-{[N-(4-pyridyl)methyl]carbamoyl}ferrocene (2) have been studied as ligands in group-12 metal bromide complexes. The reactions of 1 with CdBr2 x 4H2O and HgBr(2) at 1:1 mole ratio gave the discrete tetracadmium complex [Cd2(micro-Br)2(-1kappa2O,N2)2[micro-1kappa2O,N2:2kappaP-(C5H4N)CH2NHC(O)fcPPh2-CdBr3]2] (7; fc = ferrocene-1,1'-diyl) and the halogeno-bridged dimer [[Hg(micro-Br)Br(-kappaP)]2] (8), respectively. In the presence of acetic acid, the CdBr2-1 system furnished a zwitterionic complex featuring protonated 1 as the P-monodentate donor, [CdBr3[Ph2PfcC(O)NHCH2(C5H4NH)-kappaP]] x H2O (6 x H2O). Under neutral conditions, compound , whose terminal donor groups are better arranged for the formation of extended assemblies, gave rise to one-dimensional coordination polymers [MBr2[micro(P,N)-]](n) (M = Cd, 4; M = Hg, ). The crystal structures of 2 x H2O, its corresponding phosphine oxide (3 x H2O), and complexes 4, 5, 6 x H2O, and have been determined, revealing extensive hydrogen bonding interactions in the solid state.

Photochemical hydrogen production from water using the new photocatalyst [{(bpy) 2Ru(dpp)} 2RhBr 2](PF 6) 5

The synthesis, electrochemical, and photochemical properties of the new photocatalyst [{(bpy) 2Ru(dpp)} 2RhBr 2](PF 6) 5 (bpy = 2,2′-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine) which couples two ruthenium light absorbing metal centers to a reactive rhodium center is reported. The substitution of the bromide in lieu of the chloride in the RhX 3· nH 2O starting material provides the bromo analog in high yield and purity. The basic chemical properties of the bromide complex are very similar to the chloride system [{(bpy) 2Ru(dpp)} 2RhCl 2](PF 6) 5, being an efficient metal-to-ligand charge-transfer (MLCT) light absorber in the visible while possessing a lowest lying metal-to-metal charge-transfer ( 3MMCT) state. In the presence of an electron donor and visible light, [{(bpy) 2Ru(dpp)} 2RhBr 2](PF 6) 5 undergoes excited state intramolecular electron transfer affording photoinitiated electron collection on the reactive rhodium center to generate the Rh I complex, [{(bpy) 2Ru(dpp)} 2Rh I](PF 6) 5. The new complex affords photocatalytic hydrogen production from water with Φ ≈ 0.01, generating higher hydrogen yields than the chloride analog, 10.9 versus 8.2 μmol H 2 over a 4 h photolysis period.

Syntheses and crystal structures of hydrated complexes of strontium and barium bromides with 18-crown-6

Two complexes, namely, triaqua(18-crown-6)strontium dibromide monohydrate (I) and diaquabromo(18-crown-6)barium bromide (II), are synthesized. Their crystal structures are determined by X-ray diffraction analyses. For complex I, space group C2/c, a = 17.547 A, b = 10.246 A, c = 14.786 A, β = 123.08°, Z = 4. For complex II, space group Pnma, a = 17.753 A, b = 17.465 A, c = 6.629 A, Z = 4. The structures are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.056 (I) and 0.042 (II) for 2696 (I) and 2440 (II) independent reflections (CAD-4 automated diffractometer, λMoKα radiation). Both complex cations—randomly disordered [Sr(18C6)(H2O)3]2+ in complex I and [BaBr(18C6)(H2O)2]+ in complex II—are of the host-guest type. The Sr2+ (Ba2+) cation resides in the cavity of the 18-crown-6 ligand and coordinated by all six O atoms. In the structures complexes I and II, the coordination polyhedra of the Sr2+ and Ba2+ cations (coordination number 9) can be described as distorted hexagonal bipyramids with one apex at the O atom of the water molecule in complex I or at the Br− ligand in complex II and the other split apex at the O atoms of two water molecules.

Kinetics of reactions between bromoplatinum(II) complexes and silver nitrate

The kinetics of the reactions of bromide complexes [[PtenBr2], [Pt(NH3)2Br2], and [enPtBr2Pten](NO3)2 with AgNO3 are studied potentiometrically. The reactions occur in two stages with dramatically different rates. Rate constants are determined for the second stage. The kinetics of the reaction between the dimeric complex and AgNO3 are studied at 5, 15, 25, and 35°C. The activation energy is determined.

The influence of polymer–surfactant aggregates on drag reduction

When a water-soluble polymer and surfactant with addition of salt are mixed in water solution, the specific structures (aggregates) are formed, in which polymer film is formed around micelle. In a pipe flow, such aggregates take preferred orientation, according to minimum resistance principle. When the Reynolds number increases, the aggregates elongate. In this work, poly(ethylene oxide) (PEO)–cetyl trimethyl ammonium bromide (CTAB) complex formation and its effect on drag reduction was studied. It was found that PEO–CTAB aggregates reduced drag much more efficiently than these substances alone. Structure degradation appeared later and the drag reduction existed longer. Moreover, damaged structure could be partly rebuilt.

A study on the self assembly of Fe(II) and dual binding of Ni(II) porphyrazines on CT-DNA

Interaction of N , N ′, N ″, N ‴-tetramethyltetra-2,3-pyridinoporphyrazinatonickel(II), ([ Ni (2,3- tmtppa )]4+) and N , N ′, N ″, N ‴-tetramethyltetra-2,3-pyridinoporphyrazinatoiron(II), ([ Fe (2,3- tmtppa )]4+) with calf thymus DNA (CT-DNA) have been studied in 1mM phosphate buffer and low ionic strength (5 mM NaCl ) using several spectroscopic techniques: absorbance, fluorescence and circular dichroism. The 2:1 porphyrazine/DNA mole ratio, existence of moderate hypochromicity, moderate and progressive red shift and conservative ICD in the visible part of [ Fe (2,3- tmtppa )]4+ spectra suggested an outside binding with self-stacking mode. Analysis of the dramatic hypochromicity, small blue shift and bisignate ICD in the Q-band absorption region of [ Ni (2,3- tmtppa )]4+ spectra and 1:1 porphyrazine/DNA mole ratio possibly led us to the dual binding mode of this complex, i.e. at the minor and major grooves of DNA. The influence of the ionic strength on the porphyrazine-DNA binding confirmed this suggestion. The fluorescence quenching of DNA-ethidium bromide complex by porphyrazines was investigated. The values of quenching constants ( K sv ) and the rate constants of the quenching ( K q ) were determined by Stern-Volmer equation. The values of K sv have been obtained (2.07 ± 0.11) × 106 and (0.48 ± 0.01) × 106 M−1 for [ Fe (2,3- tmtppa )]4+ and [ Ni (2,3- tmtppa )]4+, respectively, at 27°C. The higher affinity of [ Fe (2,3- tmtppa )]4+ for the quenching of EB-DNA fluorescence with respect to Ni complex was attributed to self-stacking of the former along DNA helix and favorable energy transfer between EB+ and cationic porphyrazine. ΔG25 (the difference between the free energy of the native ( N ) and the denatured (D) form of DNA at 25°C), ΔHm and ΔSm (difference between enthalpy and entropy at Tm) were extracted from thermal curves. The decline in the melting temperature of DNA following the addition of porphyrazine complexes confirms that the substantial mode of Ni and Fe interaction is not intercalation. The thermodynamic results imply that both Ni and Fe complexes have a slight destabilizing effect on the DNA. A comparison between [ Ni ( tmtppa )]4+ and [ Fe ( tmtppa )]4+ indicates that the latter is more effective than the former.

Vinyl polymerization of norbornene by nickel(II) complexes bearing β‐diketiminate ligands

AbstractNorbornene polymerizations were carried out using nickel(II) bromide complexes CH{C(R)NAr}2NiBr (1, R = CH3, Ar = 2, 6 − iPr2C6H3; 2, R = CH3, Ar = 2, 6‐Me2C6H3; 3, R = CF3, Ar = 2, 6 − iPr2C6H3; 4, R = CF3, Ar = 2, 6‐Me2C6H3) in the presence of methylaluminoxane. Compound 3 is the most active norbornene polymerization catalyst of all the nickel complexes tested. The activity of theses catalysts increases with increases in steric bulk of the substituents on the aryl rings. The electronic nature of the ligand backbone also affects the activity. The resulting polynorbornenes are vinyl type by IR and NMR analyses. Copyright © 2007 John Wiley & Sons, Ltd.

Highly Enantioselective [2+2]-Cycloaddition Reactions Catalyzed by a Chiral Aluminum Bromide Complex

Enantioselective [2+2]-cycloaddition pathways to chiral cyclobutanes are rare and not generally utilized for synthesis. A new cycloaddition reaction of vinyl ethers with trifluoroethyl acrylate in the presence of a catalytic amount of chiral oxazaborolidine−AlBr3 complex is described which affords [2+2]-adducts with excellent yields and enantioselectivities. Applications of these adducts to the synthesis of synthetically valuable intermediates are also presented.

Copper(II) bromide complexes with acyclic and cyclic pyrimidine-containing phane ligands

Complexes of copper(II) bromide with cyclic and isostructural acyclic phane ligands containing derivatives of pyrimidine nucleobases (cytosine and uracil) were synthesized and characterized. In two cyclic pyrimidinophanes used, the macrocycles included two 6-methylthiocytosine and one 6-methyluracil units linked by polymethylene chains (L3) and two 6-methyluracil units linked by N-containing bridges (L5). Ligand L3 and its isostructural acyclic analogs are coordinated by the Cu2+ ion through the same donor sites (the ring N atoms of the thiocytosine units). The coordination polyhedra of the Cu atom in complexes with cyclic and acyclic ligands are different. Ligand L5 and its isostructural acyclic analog also form copper(II) complexes with different coordination polyhedra involving different donor sites. The acyclic ligand is coordinated by the Cu2+ ion via the bridging N atom, while cyclic ligand L5, via the uracil CO groups (the bridging N atoms become protonated). The resulting complexes are dielectrics.

Reactivity of triangular oxalate cluster complexes [M3Q7(C2O4)3]2− (M = Mo or W; Q = S or Se)

The reactions of the oxalate complexes [M3Q7(C2O4)3]2− (M = Mo or W; Q = S or Se) with MnII, CoII, NiII, and CuII aqua and ethylenediamine complexes in aqueous and aqueous ethanolic solutions were studied. The previously unknown heterometallic complexes [Mo3Se7(C2O4)3Ni(H2O)5]·3.5H2O (1) and K3{[Cu(en)2H2O]([Mo3S7(ox)3]2Br)}·5.5H2O (2) were synthesized. In these complexes, the oxalate clusters serve as monodentate ligands. The K(H2en)2[W3S7(C2O4)3]2Br·4H2O salt (3) was isolated from solutions containing CoII, NiII, or CuII aqua complexes and ethylenediamine. The reaction of [Mo3Se7(C2O4)3]2− with HBr produced the bromide complex [Mo3Se7Br6]2−, which was isolated as (Bu4N)2[Mo3Se7Br6] (4). Complexes 1–3 were characterized by X-ray diffraction, IR spectra, and elemental analysis. The formation of 4 was detected by electrospray mass spectrometry.

Effect of Salt and Surfactant Concentration on the Structure of Polyacrylate Gel/Surfactant Complexes

Small-angle X-ray scattering was used to elucidate the structure of crosslinked polyacrylate gel/dodecyltrimethylammonium bromide complexes equilibrated in solutions of varying concentrations of surfactant and sodium bromide (NaBr). Samples were swollen with no ordering (micelle free), or they were collapsed with either several distinct peaks (cubic Pm3n) or one broad correlation peak (disordered micellar). The main factor determining the structure of the collapsed complexes was found to be the NaBr concentration, with the cubic structure existing up to approximately 150 mM NaBr and above which only the disordered micellar structure was found. Increasing the salt concentration decreases the polyion mediated attractive forces holding the micelles together causing swelling of the gel. At sufficiently high salt concentration the micelle-micelle distance in the gel becomes too large for the cubic structure to be retained, and it melts into a disordered micellar structure. As most samples were above the critical micelle concentration, the bulk of the surfactant was in the form of micelles in the solution and the surfactant concentration thereby had only a minor influence on the structure. However, in the region around 150 mM NaBr, increasing the surfactant concentration, at constant NaBr concentration, was found to change the structure from disordered micellar to ordered cubic and back to disordered again.

Interaction of Saffron Carotenoids as Anticancer Compounds with ctDNA, Oligo (dG.dC)15, and Oligo (dA.dT)15

Crocin and crocetin are two important natural saffron carotenoids, which, along with dimethylcrocetin (DMC) as a semi-synthetic product, are responsible for its color. Many biological properties of saffron have been reported, among which the anticancer property is the most important. Some anticancer drugs have direct interaction with DNA, and thus the present study attempted to investigate the interaction of three major saffron carotenoids-crocin, crocetin, and DMC--with calf thymus DNA (ctDNA) and oligonucleotides. The spectrophotometric data showed some changes in ctDNA absorption spectra due to the formation of complex with saffron extract and each of these three components. Also, all the three components caused the quenching of the fluorescence emission of ctDNA-ethidium bromide complex. The Scatchard analysis of these data indicated a noncompetitive manner for quenching, which is accompanied by the outside groove-binding pattern. The circular dichroism (CD) spectra also indicated the nonintercalative binding and induction of the conformational changes, and B to C transition in ctDNA structure and then unstacking of ctDNA bases at higher concentrations of the carotenoids. The CD spectra of G.C and A.T oligonucleotides after addition of these carotenoids indicated the transition from B- to C-DNA, which is very similar to the ctDNA spectral changes. The DeltaG(H(2)O), the best parameter for the estimation of macromolecule stability, was determined for ctDNA denaturation using dodecyl trimethylammonium bromide in the absence and presence of crocin, crocetin, or DMC. Our results showed a decrease in the Delta G(H(2)O), indicating the ctDNA destabilization due to its interaction with the mentioned ligands. In conclusion, the results show that saffron and its carotenoids interact with DNA and induce some conformational changes in it. Of these carotenoids, the order of potential of interaction with DNA is crocetin > DMC >> crocin.

Unusual Influence of the Temperature on the Standard Rate Constants of Charge Transfer for the Eu(III)/Eu(II) Redox Couple in Chloride-Bromide Melts

The influence of bromide ions and temperature on the standard rate constants of the Eu(III)/Eu(II) redox reaction was determined. Cyclic voltammetry was used for the calculation of the kinetic parameters. It was shown that in NaCl-KCl (equimolar mixture)-NaBr (15 wt%)-EuCl3 melts increase of the temperature from 973 K up to 1023 K leads to a drastical decrease of the standard rate constant ks for the Eu(III)/Eu(II) redox reaction. This unusual influence of the temperature on the k s value was explained by a change of the electron transfer mechanism. It is suggested that at 1023 K another mechanism becomes dominant - the transfer of electrons through dissolved bromine in the melt. Bromine appeared in the melt due to the decomposition of chloride-bromide or bromide complexes of Eu(III), and the concentration of bromine in the melt increased with the growth of temperature.

Copper complexes with N-allylisoquinolinium halides: Synthesis and crystal structures of [C9H7N(C3H5)]2CuIICl2.86Br1.14, [C9H7N(C3H5)CuIBr2] · H2O, and [C9H7N(C3H5)CuIBr2

Crystals of the copper bromide complexes with N-allylisoquinolinium halides of the composition [C9H7N(C3H5)]2CuIICl2.86Br1.14 (I), [C9H7N(C3H5)]CuIBr2 · H2O (II), and [C9H7N(C3H5)]CuIBr2 (III) are prepared by ac electrochemical synthesis, and their structures are studied by X-ray diffraction analysis (DARCh-1 (for I) and KUMA/CCD (for II and III) diffractometers). The crystals of compound I are monoclinic: space group P21/n, a = 15.053(5) A, b = 10.486(4) A, c = 17.179(10) A, γ = 109.77(3)°, V = 2552(4) A3, Z = 4. The crystals of complex II are triclinic: space group P\(\overline 1 \), a = 7.040(1) A, b = 7.610(2) A, c = 12.460(2) A, α = 79.54(3)°, β = 86.73(3)°, γ = 89.51(1)°, V = 655.4(2) A3, Z = 2. The crystals of complex III are monoclinic: space group P21/n, a = 12.799(1) A, b = 7.692(1) A, c = 13.491(1) A, β = 111.08(1)°, V = 1239.3(2) A3, Z = 4. The structure of compound I is built of the CuIIX42− tetrahedra and N-allylisoquinolinium cations united by the C-H···X contacts into corrugated layers. The crystal structure of π-complex II is formed of dimers of the composition [C9H7(C3H5)]2 Cu2IBr4 forming layers in the direction of the z axis due to the C-H···X contacts. An important role in structure formation belongs to water molecules that cross-link the organometallic layers through the O-H···X contacts into a three-dimensional framework. When kept in the mother liquor for 6 months, the crystals of compound II transformed into crystals of compound III, whose structure consists of {[C9H7(C3H5)]2Cu2IBr4}n columns united through the C-H···Br contacts (H···Br 2.84(3)−2.92(4) A) into a three-dimensional framework.

2,6-Bis(oxazolinyl)phenylnickel(II) Bromide and 2,6-Bis(ketimine)phenylnickel(II) Bromide: Synthesis, Structural Features, and Redox Properties

2,6-Bis(oxazolinyl)phenylnickel bromide complexes [NiBr(R,R‘-Phebox)] (2) were synthesized via two synthetic routes (A and B). In route A, selective bis-ortho lithiation of [R,R‘-PheboxBr], followed by a transmetalation reaction with [NiBr2(PEt3)2], yielded not only complexes 2 with an η3-mer-N,C,N‘-bonded Phebox ligand but also [NiBr(R,R‘-Phebox)(PEt3)2], 7, where the nickel center is η1-C bonded to the intra-annular Cipso of the Phebox ligand. Coordination of two PEt3 ligands completes the square-planar coordination sphere of the Ni center in 7. When R = t-Bu, R‘ = H, only complex 7c was formed. Alternatively, when route B (oxidative addition with [Ni(cod)2], cod = cyclooctadiene) was followed, selective formation of complexes 2 was observed. X-ray crystal structures were obtained for [NiBr-(i-Pr,H-Phebox)] (2b) and [NiBr(bis(ketimine)phenyl)] (3). The Ni centers have square-planar geometries with a planar, η3-mer-N,C,N‘ coordination of the terdentate ligand systems. Complexes 2 were found to be inactive as catalysts in the atom-transfer radical polymerization (ATRP) reaction of methyl methacrylate (MMA) and in the atom-transfer radical addition (ATRA, Kharasch addition) reaction of CCl4 to MMA. This is ascribed to the relatively high oxidation potential of NiII−Phebox complexes, which excludes the (reversible) formation of a d7-NiIII−Phebox complex, a crucial condition for subsequent reactions. Cyclovoltammetry (CV) experiments ((n-Bu)4NBr as supporting electrolyte) showed no electrochemical waves between −1.00 and +1.50 V (Ag/AgCl reference electrode, (n-Bu)4NBr as supporting electrode). Theoretical calculations showed that the energy (Eox) needed for the oxidation reaction occurring during the CV experiments is considerably higher for [NiBr(Me,Me-Phebox)] (1.87 eV) and [NiBr(bis(ketimine)phenyl)] (1.90 eV) than for [NiBr(NCN)] (1) (1.45 eV).

An iodide/anion exchange route to benzimidazolylidene silver complexes from benzimidazolium iodide: Crystal structures of N, N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate

Syntheses of N, N′-dibutylbenzimidazolylidene silver complexes having chloride, nitrate or cyanide as an anion part through an iodide/anion exchange from N, N′-dibutylbenzimidazolium iodide are described, representing a practical route to benzimidazolylidene silver complexes from readily accessible benzimidazolium iodide. The crystal structures of N, N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate have been determined, showing a close ligand-unsupported Ag–Ag interaction in [(NHC) 2]Ag +[AgX 2] − and a “T” shape geometry about the silver(I) cation in complexes of chloride, bromide and cyanide, but a nearly linear shape in the bis( N, N′-dibutylbenzimidazolylidene) silver complex [ ( NHC ) 2 Ag ] + NO 3 - with non-coordinating nitrate anion.

Chiral Oxazaborolidine—Aluminum Bromide Complexes Are Unusually Powerful and Effective Catalysts for Enantioselective Diels—Alder Reactions.

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Synthesis of the first bromide complexes of the triple-decker type

Synthesis of the first bromide complexes of the triple-decker type

Anion Detection Driven by a Surprising Internal Hydrogen-Bonding Association in a Dinuclear Rhenium(I) Complex

A neutral dinuclear rhenium(I) bipyridinetricarbonyl bromide complex has been investigated with a range of anions, giving a remarkable binding affinity for dihydrogenphosphate. These studies highlight that anion sensing can be achieved with structurally simple species provided that the compound adopts an unconventional conformation, through, for example, intramolecular hydrogen bonding in solution.

Oxidative Addition Reactions of Alkyl Halides with the Group 13 Carbene Analogue [In{N(Dipp)C(Me)}2CH] (Dipp = 2,6-iPr2C6H3)

Reactions of the well-defined two-coordinate indium "carbene analogue" [In{N(Dipp)-C(Me)}2CH] (Dipp=2,6-iPr2C6H3) have been studied. Reactions of MeI, iPrI, and tBuI with [In{N(Dipp)C(Me)}2CH] formed by the in situ reaction of InI, [K{N(SiMe3)2}], and the iminoenamine ligand precursor successfully yielded the oxidative addition products [InRI{N(Dipp)C(Me)}2CH] (R=Me, iPr, tBu). The results of NMR investigations, which indicated the formation of a series of four-coordinate indium(III) complexes in C6D6 solution, were confirmed in the solid-state by single-crystal X-ray diffraction. Similar reactions employing alkyl bromides were unsuccessful and resulted in the isolation of the corresponding iodides, apparently by metathesis of the bromide oxidative addition product with KI formed during the initial InI metathesis. Reactions of isolated samples of [In{N(Dipp)C(Me)}2CH] with iPrBr and tBuBr, however, were straightforward and resulted in the successful isolation of the analogous iso-propyl and tert-butyl indium(III) bromide complexes. These were also fully characterized by 1H and 13C NMR and single-crystal X-ray diffraction experiments. In contrast, no reaction was observed between [In{N(Dipp)-C(Me)}2CH] and aryl halides or alkyl chlorides.