Nickel(II) and copper(II) complexes with humic acid anions and their derivatives

Complexation of Ni(II) and Cu(II) in aqueous solutions with anions of humic acids, extracted from naturally oxidized coal, and with their hydroxymethyl derivatives is studied spectrophotometrically and potentiometrically. The complexation stoichiometry and the stability constants of the complexes are determined.     

Monoesterase activity of a purple acid phosphatase mimic with a cyclam platform

The synthesis and characterization of a novel dinucleating ligand L (L=4,11-dimethyl-1,8-bis{2-[N-(di-2-pyridylmethyl)amino]ethyl}cyclam) and its μ-oxo-bridged diferric complex [(H(2)L){Fe(III)(2)(O)}(Cl)(4)](2+) are reported. This diiron(III) complex is the first example of a truly functional purple acid phosphatase (PAP) mimic as it accelerates the hydrolysis of the activated phosphomonoester 2,4-dinitrophenyl phosphate (DNPP). The spectroscopic and kinetic data indicate that only substrates that are monodentately bound to one of the two ferric ions can be attacked by a suitable nucleophile. This is, most probably, a terminal iron(III)-bound hydroxide. DFT calculations support this assumption and also highlight the importance of secondary interactions, exerted by the protonated cyclam platform, for the positioning and activation of the iron(III)-bound substrate. Similar effects are postulated in the native enzyme but addressed in PAP mimics for the first time.     

Reactivity of potassium tetracyanomercurate with Ag(I), Ni(II) And Co(II)

Potentiometric and conductometric studies on the reactions between K(2)Hg(CN)(4) and Ag(I), Ni(II), Co(II) are reported. The possibility of determination of these metal ions has been evaluated and some titration data are reported.     

Reactivity of copper(II)-alkylperoxo complexes

Copper(II) complexes 1a and 1b, supported by tridentate ligand bpa [bis(2-pyridylmethyl)amine] and tetradentate ligand tpa [tris(2-pyridylmethyl)amine], respectively, react with cumene hydroperoxide (CmOOH) in the presence of triethylamine in CH(3)CN to provide the corresponding copper(II) cumylperoxo complexes 2a and 2b, the formation of which has been confirmed by resonance Raman and ESI-MS analyses using (18)O-labeled CmOOH. UV-vis and ESR spectra as well as DFT calculations indicate that 2a has a 5-coordinate square-pyramidal structure involving CmOO(-) at an equatorial position and one solvent molecule at an axial position at low temperature (-90 °C), whereas a 4-coordinate square-planar structure that has lost the axial solvent ligand is predominant at higher temperatures (above 0 °C). Complex 2b, on the other hand, has a typical trigonal bipyramidal structure with the tripodal tetradentate tpa ligand, where the cumylperoxo ligand occupies an axial position. Both cumylperoxo copper(II) complexes 2a and 2b are fairly stable at ambient temperature, but decompose at a higher temperature (60 °C) in CH(3)CN. Detailed product analyses and DFT studies indicate that the self-decomposition involves O-O bond homolytic cleavage of the peroxo moiety; concomitant hydrogen-atom abstraction from the solvent is partially involved. In the presence of 1,4-cyclohexadiene (CHD), the cumylperoxo complexes react smoothly at 30 °C to give benzene as one product. Detailed product analyses and DFT studies indicate that reaction with CHD involves concerted O-O bond homolytic cleavage and hydrogen-atom abstraction from the substrate, with the oxygen atom directly bonded to the copper(II) ion (proximal oxygen) involved in the C-H bond activation step.     

Synthesis of chiral SalenZn(II) and its coordination with imidazole derivatives and amino acid ester derivatives

A chiral complex, SalenZn(II) (S), was synthesized and characterized. Its coordination with imidazole derivatives and amino acid ester derivatives was studied by UV-vis spectrophotometric titrations and CD spectroscopy. The binding constants decreased in the order K (Im)>K (2-MeIm)>K (2-Et-4-MeIm)>K (N-MeIm) for imidazole derivatives, and K (AlaOMe)>K (PheOMe)>K (ValOMe) for amino acid ester derivatives with the same configuration and K _D >K _L for amino acid esters with different configuration. CD spectra can quantify the strength of SalenZn(II)-ligand interactions, giving results consistent with the magnitudes of the binding constants. Moreover the minimum energy conformations of the adducts were obtained by simulated annealing, and quantum chemical calculations were performed based on those conformations to explain experimental results at the molecular level.     

Nickel(II)-catalyzed asymmetric alkylation of acyclic oxocarbenium ions with carboxylic acid derivatives

A nickel(II)-catalyzed asymmetric alkylation of acyclic oxocarbenium ions generated in situ from corresponding acetals with carboxylic acid derivatives to prepare β-alkoxyl carbonyl moieties with diverse α-substituents has been disclosed. The method exhibited broad scope of acetals and carboxylic acid derivatives with excellent enantioselectivity and good functional group compatibility, and can be conducted in a gram-scale without obvious loss of efficiency.     

Homoligand and mixed-ligand complexes of mercury(II) with aspartic acid and iminodiacetic acid and its derivatives

The formation of homoligand mercury(II) complexes with aspartic acid (H₂Asp) and aspartate-chelant mixed-ligand mercury(II) complexes with iminodiacetic acid (H₂Ida, IDA), 2-hydroxyethyliminodiacetic acid (H₂Heida, HEIDA), and nitrilotriacetic acid (H₃Nta, NTA) in an aqueous perchlorate medium was studied by spectrophotometry and pH-potentiometric titration. The following complexes were identified: [Hg(OH)Asp]^?, [HgAsp₂]^2?, [Hg(Asp)Ida]^2?, [Hg(Asp)Heida]^2?, and [Hg(Asp)Nta]^3?. The logarithms of their stability constants are, respectively, 11.74 ± 0.12, 20.18 ± 0.17, 20.11 ± 0.10, 19.82 ± 0.09, 19.48 ± 0.11, and 20.58 ± 0.07 (μ = 0.1 (NaClO₄), t = (20 ± 2)°C). The hydrogen and hydroxyl competition regions were located in the systems, and relationships between the molar yields of complex species and the reactant concentrations were established. The protonation and dissociation constants of aspartic acid were derived from pH-potentiometric titrations. Experimental data were analyzed using mathematical models allowing one to judge the existence of various complex species in the solution and to identify the species that are sufficient to reproduce the observed data.     

Liquid-liquid extraction of lead(II) with tributyl phosphate

Tributyl phosphate [30% solution in isobutyl methyl ketone (IBMK)] is used for the quantitative extraction of microgram amounts of lead from 3M hydrochloric acid containing lithium chloride (2M) as salting-out agent. It is then stripped from the organic phase with water and determined colorimetrically as its orange-red complex with 4-(2-pyridylazo)resorcinol at 520 nm. TBP alone cannot quantitatively extract lead in the absence of salting-out agents. The IBMK used as diluent does not extract lead under the conditions used. The period of equilibration needed is 5 min. Lead can be extracted in the presence of up to 100 times as much of certain other ions. The method is found to be applicable to analysis of gun-metal.     

Reactivity studies of cyclopentadienyl ruthenium(II), osmium(II) and pentamethylcyclopentadienyl iridium(III) complexes towards 2-(2′-pyridyl)imidazole derivatives

The reaction of [CpRu(PPh₃)₂Cl] and [CpOs(PPh₃)₂Br] with chelating 2-(2′-pyridyl)imidazole (N ∩ N) ligands and NH₄PF₆ yields cationic complexes of the type [CpM(N ∩ N)(PPh₃)]⁺ (1: M = Ru, N ∩ N = 2-(2′-pyridyl)imidazole; 2: M = Ru, N ∩ N = 2-(2′-pyridyl)benzimidazole; 3: M = Ru, N ∩ N = 2-(2′-pyridyl)-4,5-dimethylimidazole; 4: M = Ru, N ∩ N = 2-(2′-pyridyl)-4,5-diphenylimidazole; 5: M = Os, N ∩ N = 2-(2′-pyridyl)imidazole; 6: M = Os, N ∩ N = 2-(2′-pyridyl)benzimidazole). They have been isolated and characterized as their hexafluorophosphate salts. Similarly, in the presence of NH₄PF₆, [Cp∗Ir(μ-Cl)Cl]₂ reacts in dry methanol with N ∩ N chelating ligands to afford in excellent yield [Cp∗Ir(N ∩ N)Cl]PF₆ (7: N ∩ N = 2-(2′-pyridyl)imidazole; 8: N ∩ N = 2-(2′-pyridyl)benzimidazole). All the compounds have been characterized by infrared and NMR spectroscopy and the molecular structure of [1]PF₆, [2]PF₆ and [7]PF₆ by single-crystal X-ray structure analysis.     

Reactivity of pyridine-2,4,6-tricarboxylic acid toward Zn(II) salts under different reaction conditions

Pyridine-2,4,6-tricarboxylic acid (ptcH(3)) readily reacts with a Zn(II) salt at room temperature to form different products depending upon the presence or absence of pyridine in the reaction mixture. In the presence of pyridine, the ligand breaks to form infinitely zigzag coordination polymers with the empirical formula [Zn(Ox)(py)(2)]n(Ox = oxalate, py = pyridine). The backbone is formed from Zn(II)-oxalate where two pyridine molecules are coordinated to each Zn(II) ion giving it hexacoordination. The orientation of the bound pyridines is slightly different when Zn(II)-nitrate is used compared to that when Zn(II)-sulfate (or acetate) salt is used. In absence of pyridine, the ligand remains intact and forms a mixture of a carboxylate-bridged coordination polymer and a discrete carboxylate-bridged 12-membered metallomacrocycle.     

Reactivity of superoxide radical anion and hydroperoxyl radical with alpha-phenyl-N-tert-butylnitrone (PBN) derivatives

Nitrones have exhibited pharmacological activity against radical-mediated pathophysiological conditions and as analytical reagents for the identification of transient radical species by electron paramagnetic resonance (EPR) spectroscopy. In this work, competitive spin trapping, stopped-flow kinetics, and density functional theory (DFT) were employed to assess and predict the reactivity of O(2)(*-) and HO(2)(*) with various para-substituted alpha-phenyl-N-tert-butylnitrone (PBN) spin traps. Rate constants of O(2)(*-) trapping by nitrones were determined using competitive UV-vis stopped-flow method with phenol red (PR) as probe, while HO(2)(*) trapping rate constants were calculated using competition kinetics with 5,5-dimethylpyrroline N-oxide (DMPO) by employing EPR spectroscopy. The effects of the para substitution on the charge density of the nitronyl-carbon and on the free energies of nitrone reactivity with O(2)(*-) and HO(2)(*) were computationally rationalized at the PCM/B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) level of theory. Theoretical and experimental data show that the rate of O(2)(*-) addition to PBN derivatives is not affected by the polar effect of the substituents. However, the reactivity of HO(2)(*) follows the Hammett equation and is increased as the substituent becomes more electron withdrawing. This supports the conclusion that the nature of HO(2)(*) addition to PBN derivatives is electrophilic, while the addition of O(2)(*-) to PBN-type compounds is only weakly electrophilic.     

Cobalt(II) and nickel(II) complexes with 1-amino-8-hydroxynaphthalene-2,4-disulfonic acid in condensation reactions with aromatic carbonyl derivatives

The condensation reaction of cobalt(II) and nickel(II) complexes with 1-amino-8-hydroxynaphthalene-2,4-disulfonic acid and aromatic carbonyl compounds (benzoin and 2-hydroxy-1-naphthaldehyde) was carried out. Four new complexes (I–IV) were synthesized. The compounds were identified by elemental analysis, powder X-ray diffraction, thermogravimetry, magnetic susceptibility, IR and diffuse reflection spectroscopy, and EXAFS. The spatial arrangement of the donor centers of the ligands in the coordination units (tetrahedral for I, octahedral for II and III, and square planar for IV) was determined.     

Reactivity of novel N,N'-diphosphino-silanediamine-based rhodium(I) derivatives

The coordination abilities of the novel N,N'-diphosphino-silanediamine ligand of formula SiMe(2)(NtolPPh(2))(2) (SiNP, 1) have been investigated toward rhodium, and the derivatives [RhCl(SiNP)](2) (2), [Rh(SiNP)(COD)][BF(4)] (3), and Rh(acac)(SiNP) (4) have been synthesized. The stability of the dinuclear frame of [RhCl(SiNP)](2) (2) toward incoming nucleophiles has been shown to be dependent on their π-acceptor ability. Indeed, the mononuclear complexes RhCl(SiNP)(L) (L = CO, 5; CN(t)Bu, 6) have been isolated purely and quantitatively upon reaction of 2 with CO and CN(t)Bu, respectively. Otherwise, PPh(3) and RhCl(SiNP) equilibrate with Rh(Cl)(SiNP)(PPh(3)) (7). Carbon electrophiles such as MeI and 3-chloro-1-proprene afforded the oxidation of rhodium(I) to rhodium(III) and the formation of RhCl(2)(η(3)-C(3)H(5))(SiNP) (8) and Rh(Me)(I)(SiNP)(acac) (10), respectively. The methyl derivative 10 is thermally stable and does not react either with CO or with CN(t)Bu even in excess. Otherwise, RhCl(2)(η(3)-C(3)H(5))(SiNP) (8) is thermally stable but reacts with CO, affording 3-chloro-1-proprene and RhCl(SiNP)(CO) (5). Finally, upon reaction of Rh(acac)(SiNP) (4) and 3-chloro-1-proprene, RhCl(acac)(η(1)-C(3)H(5))(SiNP) (9a) and [Rh(acac)(η(3)-C(3)H(5))(SiNP)]Cl (9b) could be detected at 233 K. At higher temperatures, 9a and 9b smoothly decompose, affording the dinuclear derivative [RhCl(SiNP)](2) (2) and the CC coupling product 3-allylpentane-2,4-dione.     

Ni(II) complexes with 8-aminoquinoline derivatives

Some Ni(II) complexes with 5,7-dicloro-8-aminoquinoline (dcaq), 5,7-dibromo-8-aminoquinoline(dbaq) and 5,7-diiodo-8-aminoquinoline(diaq) are described. The compounds are of stoichiometry NiL₂X₂(L= dcaq, dbaq, diaq; X= NO^?₃ and L= dbaq; X= Cl^?, Br^?, I^?, NCS^?) and NiLX₂·H₂O(L= dcaq, diaq; X= Cl^?). The electronic spectra and magnetic susceptibility data at room temperature, are consistent with octahedral geometry for the Ni(II) in each compound. I.r. spectra show the presence of ionic and bridging nitrate groups in the compounds NiL₂(NO₃)₂(L= dcaq, dbaq, diaq) and we assign them polymeric structures. Polymeric structures with bridging chloride are proposed for the compounds NiLCl₂·H₂O(L= dcaq, diaq) and monomeric octahedral structures for NiL₂X₂(L= dbaq; X= Cl, Br, I, NCS).     

The Reactivity of Mn(II) and Ti(IV) Dialkylamides with Organophosphorus Esters

Abstract

Treatment of dialkyl (or diaryl) phosphites with titanium tetrakis-(diethylamide) at room temperature resulted in a smooth displacement of both ester functions by the diethylamino groups to give bis(diethylamino) phosphorus acid (58–65%). The same results are obtained at ?40° and no evidence of an intermediate product was detected using ¹H n.m.r. techniques. Treatment of dimethyl phosphite with titanium tetrakis(n-dibutylamide) resulted in isolation of two products which were identified as bis-(n-dibylamino) phosphorus acid (52%) and methyl-(n-dibutylamino) phosphorus acid (21%). On the other hand, trialkyl (triaryl) phosphates are inert to the titanium reagents.     

New insights into the mechanism of purple acid phosphatase through (1)H NMR spectroscopy of the recombinant human enzyme

Proton NMR spectra of FeIII-FeII recombinant single polypeptide human PAP (recHPAP) have been measured at, above, and below its pH optimum, as have the spectra of inhibited forms containing fluoride and phosphate, analogues of the substrates hydroxide and phosphate esters, respectively. The results demonstrate that binding of inhibitory anions to the dinuclear mixed-valent site of recHPAP is controlled by protonation of a ligand to the dinuclear center. Thus, the group that is responsible for pKa,1 in the enzymatic activity versus pH profile functions as a "gatekeeper", whose protonation state controls anion binding to the mixed-valent dinuclear site. The correlation between the pKa values observed in kinetics studies and for the spectroscopic changes strongly suggests that this group is the nucleophilic hydroxide that attacks the phosphate ester substrate.     

New Fe(III)Zn(II) complex containing a single terminal Fe-O(phenolate) bond as a structural and functional model for the active site of red kidney bean purple acid phosphatase

The new heterodinuclear complex [Fe(III)Zn(II)(BPBPMP)(OAc)(2)]ClO(4) (1) with the unsymmetrical N(5)O(2) donor ligand 2-bis[((2-pyridylmethyl)-aminomethyl)-6-[(2-hydroxybenzyl)(2-pyridylmethyl)]-aminomethyl]-4-methylphenol (H(2)BPBPMP) has been synthesized and characterized by X-ray crystallography, which reveals that the complex cation has an Fe(III)Zn(II)(mu-phenoxo)-bis(mu-carboxylato) core. Solution studies of 1 indicate that a pH-induced change of the bridging acetate occurs, and the formation of an active [(OH)Fe(III)Zn(II)(OH(2))] species as a highly efficient catalyst under weakly acidic conditions for phosphate diesters hydrolysis is proposed.     

Reactivity of α,α-dipyrrolylmethene in reactions with some Co(II) and Cu(II) complexes

Reactivity of 3,3′,5,5′-tetramethyl-4,4′dibutyldipyrrolylmethene (HL) in reactions Co(II) and Cu(II) acetates, acetylacetonates, and valinates in DMF (298.15 K) was estimated by spectrophotometric and calorimetric titration methods. The product of the exchange reaction between HL and Co acetate or acetylacetonate was found to be CoL₂ complex. With an excess of Cu(II) acetate or acetylacetonate, the reaction resulted in mixed-ligand complexes CuL(AcO) and CuL(Acac), while with an excess of HL, the CuL₂ complex was formed. Irrespective of the reagent concentration ratios, the exchange reactions with Cu(II) and Co(II) valinates gave ML(Val) complexes. Thermodynamic parameters of HL reactions with Cu(II) and Co(II) acetates, acetylacetonates, and valinates were determined.     

Kinetics of zinc(II) cloride extraction with tributyl phosphate

The equilibrium and rate of solvent extraction of zinc chloride complexes from HCl solutions into benzene solutions of tributyl phosphate (TBP) have been studied. The extracted species are discussed in the light of the results. The extraction was found to be first order with respect to both Zn(II) and TBP, and zero order for HCl. The rate-controlling steps are discussed and the rate constants for these reactions are calculated.