Studies on the reactivity of cis-RuCl2 fragment in Ru(PPh3)2(TaiMe)Cl2 with N,N-chelators (TaiMe = 1-methyl-2-(p-tolylazo)imidazole). Spectral and electrochemical characterisation of the products

Dechlorination of Ru(PPh₃)₂(TaiMe)Cl₂ (TaiMe = p-Me-C₆H₄-N=N-C₃H₂NN(1)-Me (1), 1-methyl-2-(p-tolylazo)imidazole) has been carried out in acetone solution by Ag⁺ and reacted with N,N’-chelators to synthesise [Ru(PPh₃)₂ (TaiMe)(N,N’)]²⁺. The complexes have been isolated as their perchlorate salts. The N,N’ chelators are 1-alkyl-2-(phenylazo)imidazoles (PaiX, X = Me, Et, CH₂Ph); 2-(arylazo)pyridines, (Raap,p-R-C₆H₄-N=N-C₅H₄N; R = H, Me, Cl); 2-(arylazo)pyrimidines (Raapm,p-R-C₆H₄-N=N-C₃N₂H₂; R = H, Me, Cl); 2,2’-bipyridine (bpy) and 1,10-phenanthroline (o-phen). Unsymmetrical N,N’ chelators may give two isomers and this is indeed observed. The¹H NMR spectral data refer to the presence of two isomers in the mixture in different proportions. With consideration of coordination pairs in the order of PPh₃, PPh₃; N,N (N refers to N(immidazole)) and N’,N (N’ refers to N(azo)), the complexes have been characterised astrans-cis-cis andtrans-trans-trans configuration; the former predominates in the mixture. Electrochemical studies exhibit high potential Ru(III)/Ru(II) couple and quasireversible N=N reduction. Electronic spectra show high intensity (ε ∼ 10⁴) MLCT transition in the visible region (520 ±10) nm along with a shoulder (ε ∼ 10³) in the longer wavelength region.     

Ruthenium azo complexes: Synthesis,spectra, and electrochemistry of dithiocyanato-bis{1-(alkyl)-2-(arylazo)imidazole}ruthenium(II)

Silver-assisted aquation of blue cis-trans-cis-RuCl₂(RAaiR’)₂ (I) leads to the synthesis of solvento species, blue-violet cis-trans-cis-[Ru(OH₂)₂(RAaiR’)₂](ClO₄)₂ (II), where RAaiR’ = p-R-C₆H₄-N=N-C₃H₂-NN, abbreviated as N,N′ chelator (N(imidazole) and N(azo) represent N and N′, respectively); R = H (a), p-Me (b), p-Cl(c); R′ = Me (III), Et (IV), Bz (V), that reacted with NCS⁻ in warm EtOH resulting in red-violet dithiocyanato complexes of the type [Ru(NCS)₂(RAaiR)₂] (IIIa–Vn). These complexes were studied by elemental analysis, UV-Vis, IR, and ¹H NMR spectroscopy and cyclic voltammetry. The solution structure and stereoretentive transformation in each step have been established from ¹H NMR results. All the complexes exhibit strong MLCT transitions in the visible region. They are redox active and display one metal-centered oxidation and successive ligand-based reductions. Linkage isomerisation was studied by changing the solvent and then by UV-Vis spectral analysis.     

Models for the active site in galactose oxidase: Structure, spectra and redox of copper(II) complexes of certain phenolate ligands

Galactose oxidase (GOase) is a fungal enzyme which is unusual among metalloenzymes in appearing to catalyse the two electron oxidation of primary alcohols to aldehydes and H₂O₂. The crystal structure of the enzyme reveals that the coordination geometry of mononuclear copper(II) ion is square pyramidal, with two histidine imidazoles, a tyrosinate, and either H₂O (pH 7.0) or acetate (from buffer,pH 4-5) in the equatorial sites and a tyrosinate ligand weakly bound in the axial position. This paper summarizes the results of our studies on the structure, spectral and redox properties of certain novel models for the active site of the inactive form of GOase. The monophenolato Cu(II) complexes of the type [Cu(L1)X][H(L1) = 2-(bis(pyrid-2-ylmethyl)aminomethyl)-4-nitrophenol and X⁻ = Cl⁻ 1, NCS⁻ 2, CH₃COO⁻ 3, ClO₄ ⁻ 4] reveal a distorted square pyramidal geometry around Cu(II) with an unusual axial coordination of phenolate moiety. The coordination geometry of 3 is reminiscent of the active site of GOase with an axial phenolate and equatorial CH₃COO⁻ ligands. All the present complexes exhibit several electronic and EPR spectral features which are also similar to the enzyme. Further, to establish the structural and spectroscopic consequences of the coordination of two tyrosinates in GOase enzyme, we studied the monomeric copper(II) complexes containing two phenolates and imidazole/pyridine donors as closer structural models for GOase. N,N-dimethylethylenediamine and N,N’-dimethylethylenediamine have been used as starting materials to obtain a variety of 2,4-disubstituted phenolate ligands. The X-ray crystal structures of the complexes [Cu(L5)(py)], (8) [H₂(L5) = N,N-dimethyl-N’,N’-bis(2-hydroxy-4-nitrobenzyl) ethylenediamine, py = pyridine] and [Cu(L8)(H₂O)] (11), [H₂(L8) = N,N’-dimethyl-N,N’-bis(2-hydroxy-4-nitrobenzyl)ethylenediamine] reveal distorted square pyramidal geometries around Cu(II) with the axial tertiary amine nitrogen and water coordination respectively. Interestingly, for the latter complex there are two different molecules present in the same unit cell containing the methyl groups of the ethylenediamine fragmentcis to each other in one molecule andtrans to each other in the other. The ligand field and EPR spectra of the model complexes reveal square-based geometries even in solution. The electrochemical and chemical means of generating novel radical species of the model complexes, analogous to the active form of the enzyme is presently under investigation.     

Thermal decomposition of some linear trinuclear schiff base complexes with acetate bridges

Ni(II)–M(II)–Ni(II) nuclear structured complexes were prepared from N,N’-bis(salicylidene)-1,3-propanediamine (LH2) and its derivatives N,N’-bis(salicylidene)-2,2’-dimethyl-1,3-propanediamine (LDMH₂) and N,N’-bis(salicylidene)-2-hydroxy-1,3-propanediamine (LOH3), where M represents one of the following metal ions; Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II). Two different μ-bridges are found between the metal nucleus of the complexes. The phenolic oxygens and acetate ions tend to form μ-bridges between the terminal Ni(II) ions and central metal(II) ion. The coordinatively bonded DMF molecules, in the complexes, were observed to abandon the structure between 160–180°C. Further heating resulted primarily in the thermal decomposition of the complexes above 310°C, whereas metal oxide residue mixtures were observed above 650°C.     

Bisphosphorylated ligands based on isomeric N,N’-phenylenedibenzimidoyl dichlorides

The Arbuzov reaction of N,N’-phenylenedibenzimidoyl dichlorides furnished new tetradentate ligands, viz., N,N’-bis[(diphenylphosphoryl)phenylmethylidene]benzenediamines, which form complexes with lanthanides.     

Kinetics and Mechanism of the Reactions of Picolinic Acid with Dichloro-{1-alkyl-2-(arylazo)imidazole}palladium(II) Complexes

The reaction between Pd(N,N′)Cl₂ [N,N′ ≡ 1-alkyl-2-(arylazo)imidazole (N,N′) and picolinic acid (picH) have been studied spectrophotometrically at λ = 463 nm in MeCN at 298 K. The product is [Pd(pic)₂] which has been verified by the synthesis of the pure compound from Na₂[PdCl₄] and picH. The kinetics of the nucleophilic substitution reaction have been studied under pseudo-first-order conditions. The reaction proceeds in a two-step-consecutive manner (A → B → C); each step follows first order kinetics with respect to each complex and picH where the rate equations are: Rate 1 = {k′₀ + k′₂[picH]₀} × [Pd(N,N′)Cl₂] and Rate 2 = {k′′₀ + k′′₂[picH]₀}[Pd(N,O)(monodentate N,N′)Cl₂] such that the first step second order rate constant (k′₂) is greater than the second step second order rate constant (k′′₂). External addition of Cl⁻ (as LiCl) suppresses the rate. Increase in π-acidity of the N,N′ ligand, increases the rate. The reaction has been studied at different temperatures and the activation parameters (Δ^‡H° and Δ^‡S°) were calculated from the Eyring plot.     

BEAMGAA with photons — the axial gradient

The extraction of uranyl nitrate by the novel extractant N,N’-dimethyl-N,N’-dioctylsuccinylamide (DMDOSA) from aqueous nitric/nitrate solutions was investigated. The effects of concentration of HNO₃ and DMDOSA on the U(VI) extraction distribution was studied. The extraction mechanism was established and the stoichiometry of the main extracted species was confirmed to be UO₂(NO₃)₂·2DMDOSA. The value of ΔH of the extraction is −23.9±1.7 kJ·mol⁻¹. A IR spectral study of the U(VI) extracted species was also made.     

Studies on solid state synthesis and the oxygenation property of cobalt (II) Schiff base (vanilline polyamine) complexes

Three new cobalt complexes were synthesized by solid-state reaction at room temperature and the resultant Co complexes reacted with two equivalent oxygen molecules at room temperature to produce the oxygenated complexes [Co·(L₁)₂·(O₂)₂](NO₃)₂·2H₂O (L₁ = N, N’-bis(4-hydroxyl-3-methoxy-benzyl)-diethylenetriamine), [Co·(L₂)₂·(O₂)₂](NO₃)₂·2H₂O (L₂ = N, N’-bis(4-hydroxyl-3-methoxy-benzyl)-triethylenetetramine), and [Co·(L₃)₂·(O₂)₂](NO₃)₂·2H₂O (L₃ = N, N’-bis(4-hydroxyl-3-methoxy-benzyl-tetraethylenepentamine). The oxygenated complexes were characterized by elemental analysis, IR (Infrared), ¹H-NMR (Nuclear Magnetic Resonance), and UV-Vis (Ultraviolet Visual) spectrometry, and TG/DTA (Thermogravimetry/Differential Thermal Analysis) analysis, and molar conductance. The coordinated oxygen contents in the oxygenated complexes were also determined by weight method. It was supposed that only one O₂ molecule coordinated to the Co ion forming a superoxo type oxygenated complex. Translated from Acta Chimica Sinica, 2006, 64(15): 1517–1522 (in Chinese)     

Syntheses, structural determination and binding studies of nine-coordinate mononuclear (EnH2)1.5 [ErIII(Ttha)] · 3H2O and (EnH2)[ErIII(Egta)(H2O)]2 · 6H2O

In this work, the title complexes, (EnH₂)_1.5[Er^III(Ttha)] · 3H₂O (I) and (EnH₂)[Er^III(Egta)(H₂O)]₂ · 6H₂O (II), where En = ethylenediamine, H₆Ttha = triethylenetetramine-N,N,N′,N″,N″’,N″′-hexaacetic acid, H₄Egta = ethyleneglycol-bis-(2-aminoethylether)-N,N,N′,N′-tetraacetic acid, have been successfully synthesized. Their structures have been characterized by IR spectroscopy and single-crystal X-ray diffraction techniques. The X-ray diffraction reveals that I is nine-coordinated and crystallizes in the monoclinic crystal space group P2/n with cell dimensions a = 17.6058(16), b = 9.6249(9), c = 20.560(2) ?, β = 109.7440(10)°, and V = 3279.1(5) ?³. Compound II is also nine-coordinated and crystallizes in the monoclinic crystal space group P2₁/n with the cell dimensions a = 12.938(6), b = 12.651(5), c = 14.943(6) ?, β = 105.441(5)°, and V = 2357.5(17) ?³. In I, each EnH₂²⁺ cation connects three adjacent [Er^III(Egta)(H₂O)]⁻ complex anions through hydrogen bonds, while in I, there are two types of EnH₂ ²⁺ anions. One is highly symmetrical, forming hydrogen bonds with two neighboring [Er^III(Ttha)]³⁻ complex anions. The other anion connects three adjacent [Er^III(Ttha)]³⁻ complex anions through hydrogen bonds. These hydrogen bonds lead to the formation of 2D ladder-like layer structure.     

Gold(I)-diphenylphosphinomethane–arylazoimidazole: synthesis and multinuclear NMR investigation

Reaction of [Au₂(dppm)Cl₂] with AgOTf in CH₂Cl₂ medium followed ligand addition and leads to [Au₂(dppm)(RaaiR′)](OTf) [RaaiR′ = p-R–C₆H₄–N = N–C₃H₂–NN–1–R′, (1–3), abbreviated as N,N′-chelator, where N(imidazole) and N(azo) represent N and N′, respectively; R = H (a), Me (b), Cl (c) and R′ = Me (1), CH₂CH₃ (2), CH₂Ph (3), OSO₂CF₃ is the triflate anion, and dppm is the diphenylphosphinomethane-ring]. The ¹H-n.m.r. spectral measurements suggest methylene, –CH₂–, in RaaiEt gives a complex AB type multiplet while in RaaiCH₂Ph it shows AB type quartets with coupling constant of avg. 6 Hz. Considering all the moities there are a lot of different carbon atoms in the molecule which gives a lot of different peaks in the ¹³C-n.m.r spectrum. In the ¹H–¹H-COSY spectrum of the present complexes and contour peaks in the ¹H–¹³C-HMQC spectrum in the present complexes, assign the solution structure and stereoretentive transformation in each step.     

A novel series of nickel(II)-dppe-arylazoimidazole complexes. Synthesis and spectroscopic characterization

Reaction of [Ni(dppe)Cl₂/Br₂] with AgOTf in CH₂Cl₂ medium following ligand addition leads to [Ni(dppe)(OSO₂CF₃)₂] and then [Ni(dppe)(RaaiR)](OSO₂CF₃)₂ [RaaiR′ = p–R–C₆H₄–N=N–C₃H₂–NN-1–R′,(1–3), abbreviated as N,N′-chelator, where N(imidazole) and N(azo) represent N and N′, respectively; R = H (a), Me (b), Cl (c) and R′ = Me (1), CH₂CH₃ (2), CH₂Ph (3), OSO₂CF₃ is the triflate anion]. ³¹P{¹H}-NMR confirm that stable bis-chelated square planar Ni(II) azoimine–dppe complex formation with one sharp peaks. The ¹H NMR spectral measurements suggest azoimine link is present with lot of phenyl protons in the aromatic region. Considering all the moities there are a lot of different carbon atoms in the molecule which gives many different peaks in the ¹³C(¹H)-NMR spectrum. In the ¹H-¹H COSY spectrum in the present complexes and contour peaks in the ¹H-¹³C-HMQC spectrum in the present complexes, assign the solution structure and stereoretentive conformation in each complexes.     

Amination of 4,6- and 2,4-dichloropyrimidines with polyamines

Amination of a double excess of 4,6-dichloropyrimidine with various diamines in the presence of cesium carbonate in boiling dioxane quantitatively afforded the corresponding N,N′-bis(6-chloropyrimidin-4-yl) derivatives, while its reactions with tri- and tetraamines gave N,N′,N″-tris- and N,N′,N″,N‴-tetrakis(6-chloropyrimidin-4-yl) derivatives. Equimolar amounts of 2,4-dichloro- or 4,6-dichloropyrimidine and diamines reacted in the presence of Pd(0) complexes to form macrocyclic compounds containing pyrimidine fragments. Catalytic reactions of 4 equiv of diamines with 4,6-dichloropyrimidine can lead to the formation of 4,6-bis-(diamino)pyrimidines. Relations between the yield and the nature of diamine and catalytic system were found.     

Alkylation of salts ofN-(β-hydroxyalkyl)-N′-hydroxydiazeneN-oxides with alkyl halides and dimethyl sulfate

Salts ofN-(β-hydroxyalkyl)-N′-hydroxydiazeneN-oxides, RCH(OH)CH₂N(O)=NO⁻ M⁺ (R=Me, Prⁱ, or Bu^t; and M=Li, Na, K, Ag, NH₄, or Me₄N), were prepared. Their alkylation with alkyl halides R′X (X=Cl, Br, or I) and dimethyl sulfate was studied. Generally, alkylation afforded mixtures ofN-(β-hydroxyalkyl)-N′-alkoxydiazeneN-oxides RCH(OH)CH₂N(O)=NOR′ andO-alkyl-N-(β-hydroxyalkyl)-N-nitrosohydroxylamines RCH(OH)CH₂N(NO)OR′. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1996–2001, October, 1998.     

Multinuclear NMR investigation on organometallic gold(III) pentafluorophenylarylazoimidazole complexes

Reaction of [Au(C₆F₅)(tht)₂Cl](OTf) with RaaiR′ in CH₂Cl₂ medium leads to [Au(C₆F₅)(RaaiR′)Cl](OTf) [RaaiR′ = p-R–C₆H₄–N=N–C₃H₂–NN-1-R′, (1–3), abbreviated as N,N′-chelator, where N(imidazole) and N(azo) represent N and N′, respectively; R = H (a), Me (b), Cl (c) and R′ = Me (1), CH₂CH₃ (2), CH₂Ph (3), tht is tetrahydrothiophen]. The maximum molecular peak of [Au(C₆F₅)(MeaaiMe)Cl] is observed at m/z 599.51 (100 %) in the FAB mass spectrum. Ir spectra of the complexes show –C=N– and –N=N– stretching near at 1590 and 1370 cm⁻¹ and near at 1510, 955, 800 cm⁻¹ due to the presence of pentafluorophenyl ring. The ¹H-NMR spectral measurements suggest methylene, –CH₂–, in RaaiEt gives a complex AB type multiplet while in RaaiCH₂Ph shows AB type quartets. ¹³C-NMR spectrum of complexes confirm the molecular skeleton. In the ¹H-¹H-COSY spectrum as well as contour peaks in the ¹H-¹³C HMQC spectrum for the present complexes, assign the solution structure and stereoretentive conformation. The electrochemistry gives the ligand reduction peaks.     

Reaction sites of <Emphasis Type="Italic">N,N′</Emphasis>-substituted <Emphasis Type="Italic">p</Emphasis>-phenylenediamine antioxidants

The geometries of N,N′-diphenylbenzene-1,4-diamine (DPPD), N-phenyl-N′-(1-phenylethyl)benzene-1,4-diamine (SPPD), N-(4-methylpentan-2-yl)-N′-phenylbenzene-1,4-diamine (6PPD), N-propan-2-yl-N′-phenylbenzene-1,4-diamine (IPPD), N-(2-methoxybenzyl)-N′-phenylbenzene-1,4-diamine (MBPPD), and N-phenyl-N′-(2-phenylpropan-2-yl)benzene-1,4-diamine (CPPD) as well as of their dehydrogenation products were optimized by the semiempirical AM1 method. The results support the idea of stable N_B=C_X structures formation during the consecutive dehydrogenation of SPPD, 6PPD, IPPD, and MBPPD antioxidants. The biradicals formed during the second step of dehydrogenation of substituted phenylenediamines might be important for their antioxidant effectiveness. Dedicated to Professor Vladimír Kvasnička, DrSc., in honour of his 65th birthday     

Investigation on the thermal decomposition some heterodinuclear NiII-MII complexes prepared from ONNO type reduced Schiff base compounds ( M II=ZnII, CdII)

N,N′-bis(salicylidene)-1,3-propanediamine (LH₂), N,N′-bis(salicylidene)-2,2′-dimethyl-1,3-propanediamine (LDMH₂), N,N′-bis(salicylidene)-2-hydroxy-1,3-propanediamine (LOH₃), N,N′-bis(2-hydroxyacetophenylidene)-1,3-propanediamine (LACH₂) and N,N′-bis(2-hydroxyacetophenone)-2,2′-dimethyl-1,3-propanediamine (LACDMH₂) were synthesized and reduced to their phenol-amine form in alcoholic media using NaBH₄ (L^HH₂, LDM^HH₂, LOH^HH₂, LAC^HH₂ and LACDM^HH₂). Heterodinuclear complexes were synthesized using Ni(II), Zn(II) and Cd(II) salts, according to the template method in DMF media. The complex structures were analyzed using elemental analysis, IR spectroscopy, and thermogravimetry. Suitable crystals of only one complex were obtained and its structure determined using X-ray diffraction, NiLAC^H·CdBr₂·DMF₂, space group orthorhombic, Pbca, a=20.249, b=14.881, c=20.565 ? and Z=8. The heterodinuclear complexes were seen to be of [Ni·ligand·MX₂·DMF₂] structure (ligand=L^H2−, LDM^H2−, LOH^H2−, LAC^H2−, LACDM^H2−, M=Zn^II, Cd^II, X=Br⁻, I⁻). Thermogravimetric analysis showed irreversible bond breakage of the coordinatively bonded DMF molecules followed by decomposition at this temperature.     

Copper(II) complexes of 2-carbamoylethyl derivatives of linear diamines. Crystallographic evidence for amido oxygen binding prior to deprotonation of amide nitrogens

There has been considerable interest in the coordination chemistry of linear and macrocyclic amides⁽¹⁾. Deprotonation of the amide nitrogen is known to occur with various metal ions and the sites of coordination are generally considered to be the carbonyl oxygen prior to deprotonation and the amide nitrogen after deprotonation. However, oxygen binding has generally been inferred from indirect evidence^(2,3). We now report the results of some studies on the interaction of copper(II) with a series of 2-carbamoylethyl derivatives of linear diamines, namelyN,N′-bis(2-carbamoylethyl)ethylenediamine (1),N,N,N′,N′-tetrakis(2-carbamoylethyl)ethylenediamine (2)N,N′-bis(2-carbamoylethyl)trimethylenediamine (3) andN,N,N′,N′-tetrakis(2-carbamoylethyl)trimethylenediamine (4) which confirm carbonyl oxygen binding prior to amide deprotonation.     

Preparation and characterization of diethylnicotinamidium perchlorate

The title compound is the first example of N,N′-diethylnicotinamidium, [denaH]⁺, salt which has been characterized by X-ray analysis and IR spectra. [denaH]ClO₄ was obtained from the reaction mixture prepared from N,N′-diethylnicotinamide (dena) and Fe(ClO₄)₃ in ethanol without any addition of HClO₄. The proton required for protonation of dena is produced by hydrolysis of aquairon(III) cations. In the crystal structure, cations and anions are held together by ionic interactions. The cations are linked to each other by pyridinium-carbonyl N-H⋯O=C hydrogen bonds and an infinite linear chain along axis a is formed. Dedicated to Professor Milan Melník on the occasion of his 70th birthday     

<Emphasis Type="Italic">N,N’</Emphasis>-Bis(2-mercaptophenyl)propane-1,3-diamine as a new organic ligand of the N<Subscript>2</Subscript>S<Subscript>2</Subscript> type and its coordination compound with nickel(II)

A method for the synthesis of new tetradentate organic ligand of the N₂S₂ type, viz., N,N’-bis-(2-mercaptophenyl)propane-1,3-diamine has been developed, starting from 2-( tert-butyl-thio)aniline and malonyl dichloride. Coordination compound of this ligand with Ni^II according to the X-ray diffraction data has a square-planar geometry of the metal ion coordination sphere.