Ruthenium-azoimine-chloranilates Synthesis,Spectra and Electrochemistry of Ruthenium(II)-1-alkyl-2-(arylazo)imidazole-chloranilate Complexes

Ag⁺-assisted dechlorination of blue cis-trans-cis Ru(R-aai-R′)₂Cl₂ followed by the reaction with chloranilic acid (H₂CA) in the presence of Et₃N, gives a neutral mononuclear violet complex [Ru(R-aai-R′)₂(CA)]. [R-aai-R′=p-R-C₆H₄—N=N—C₃H₂—NN, abbreviated as an N,N′ chelator where N(imidazole) and N(azo) represent N and N′, respectively; R = H (a), OMe (b), NO₂ (c) and R′= Me (4), Et(5), Bz(6)]. All the complexes exhibit strong intense MLCT transitions in the visible region and weak broad bands at higher wavelength (>700 nm). Visible transitions (580–595 nm) show a negative solvatochromic effect. The cyclic voltammograms show two quasireversible to irreversible couples positive to SCE and are due to CA⁻/CA²⁻ (1.2–1.35 V) and Ru(III)/Ru(II) (1.6–1.8 V) redox processes. Three couples, negative to SCE, are assigned to CA²⁻/CA³⁻ (−0.2 to −0.3 V), and azo reductions (−0.5 to −0.7, −0.8 to −0.9 V) of the chelated R-aai-R′.     

1,10-(phenanthroline)-bis{1-alkyl-2-(arylazo)imidazole} ruthenium(II) perchlorate: Synthesis,spectral study,and electrochemistry

The hetero-tris-chelates of the formula [Ru(Phen)(RAaiR′)₂](ClO₄)₂ (Phen = 1,10-phenanthroline, RAaiR′ = 1-alkyl-2-(arylazo)imidazole, p-R-C₆H₄-N=N-C₃H₂-NN-1-R′, where R = H (a), Me (b), Cl (c) and R′ = Me (II), Et (III), CH₂Ph (IV)) have been isolated from the reaction of ctc-[RuCl₂(RAaiR′)₂] with AgNO₃ + Phen or [Ag(Phen)₂](ClO₄) in acetone at 40°C in dark followed by the addition of NaClO₄ (aq). The stereo-chemistry of the complexes have been supported by ¹H NMR data. Considering the arylazoimidazole and phenanthroline moietie there are twenty different carbon atoms in the molecule which gives a total of twenty different peaks in the ¹³C NMR spectrum of complex Ia. Cyclic voltammograms show Ru(III)/Ru(II) couple at 1.3–1.4 V vs SCE along with three successive ligand reductions. The article is published in the original.     

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.     

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.     

Synthesis,spectral characterisation and electrochemical studies of dichloro-{1-benzyl-2-(arylazo)imidazole}platinum(II) complexes and their dioxolene derivatives

1-Benzyl-2-(arylazo)imidazoles, p-RC₆H₄N=NC₃H₂-N₂1-CH₂Ph [RaaiBz (2); R=H(a), Me(b), Cl(c)], react with K₂PtCl₄ in boiling MeCN–H₂O (1:1 v/v) to give brownish-red Pt(RaaiBz)Cl₂ (3) complexes. Addition of dioxolene in the presence of Et₃N to a CHCl₃–MeOH solution of Pt(RaaiBz)Cl₂ yields green mixed complexes of composition [Pt(RaaiBz)(O,O)] [O,O = catecholate (cat) (4); 4-tert-butylcatecholate (tbcat), (5); 3,5-di-tert-butylcatecholate (dtbcat), (6); tetracholorocatecholate (tccat), (7)] which were characterised by elemental analyses, i.r., u.v.–vis.–near i.r. and ¹H-n.m.r. spectral data. The solution electronic spectra exhibit ligand-to-ligand charge-transfer (l.l.c.t) transitions in the red to near i.r. region; the position and symmetry of the band depend upon the substituent on the dioxolene and arylazoimidazole. This effect is qualitatively assigned as HOMO(dioxolene) LUMO(RaaiBz). A cyclic voltammogram of the dioxolene complex reveals two consecutive oxidative couples corresponding to catechols to semiquinones and semiquinone to quinone, respectively and the reductive couples represent azo reductions.     

Copper(I) and Silver(I) Complexes of 1-alkyl-2-(methyl)-4-(arylazo)imidazole. Synthesis, Spectral Studies and Electrochemistry

2-(Methyl)-4-(arylazo)imidazole (RLH) (1, 2) are new series of azoimidazoles. Upon treatment of alkylhalide in dry THF in presence of NaH has synthesised 1-alkyl-2-(methyl)-4-(arylazo)imidazole (RLR′) (3, 4). They belong to the azoimine family of N,N′-chelating ligand. They stabilize the Cu(I) oxidation state and we have synthesized [Cu(RLR′)₂](ClO₄) (5, 6). These complexes show a moderately intense visible band (500–600 nm) which has been assigned to 3d(Cu) → π*(ligand) transition. Ag(I) complexes of RLR′ (7, 8) are also very stable under ambient conditions and show weak transitions in the visible region. The Cu(I)-complexes show high potential Cu(II)/Cu(I) redox couple > 0.4 V vs Ag, AgCl/Cl⁻ reference electrode. All these complexes have been structurally characterized by ¹H NMR spectroscopic data.     

Synthesis, spectral characterization and redox properties of iron (II) complexes of 1-alkyl-2-(arylazo)imidazole

Iron (II) complexes of 1-alkyl-2-(arylazo)imidazoles (p-R-C₆H₄-N=N-C₃H₂NN-1-R′, R = H (a), Me (b), Cl (c) and R′ = Me (1/3), Et (2/4) have been synthesized and formulated astris-chelates Fe(RaaiR′) ₃ ²⁺ . They are characterized by microanalytical, conductance, UV-Vis, IR, magnetic (polycrystalline state) data. The complexes are low spin in character,t _2g ⁶ (Fe(II)) configurations.     

Reaction of Ru(PPh3)3Cl2 with arylazoimidazoles: spectral characterisation and redox studies of [bis-{N(1)-alkyl-2-(arylazo)imidazole}-bis-(triphenylphosphine)]-ruthenium(II) perchlorate

Ru(PPh₃)₃Cl₂ reacts with N(1)-alkyl-2-(arylazo)imidazoles, p-RC₆H₄N=NC₃H₂N₂X, [RaaiX, R = H(a), Me(b), Cl(c); X = Me(1), Et(2), Bz(3)] under refluxing conditions in EtOH to give [Ru(RaaiX)₂(PPh₃)₂](ClO₄)₂ · H₂O complexes (4–6). RaaiX is a bidentate chelator (N, N) with N(imidazole), N and N(azo), N donor centres. Three isomers are present in the mixture in which the pairs of PPh₃, N and N occupy cis–cis–trans, cis–trans–cis and cis–cis–cis, positions respectively. The isomers were identified by ¹H-n.m.r. spectra. Four signals are observed in the aliphatic zone for N(1)-X; two are of equal intensity at higher and the other two signals at lower in the ratio 1:0.3:0.2 suggesting the presence of cis–cis–cis, cis–trans–cis and cis–cis–trans-geometry. The complexes display the allowed t ₂(Ru) ^*(RaaiX) transition. Cyclic voltammetry indicates two consecutive Ru^III/II couples along with azo reductions.     

Schiff Bases Derived from 6-Amino-2<Emphasis Type="Italic">H</Emphasis>-chromen-2-one. Synthesis and <Superscript>1</Superscript>H NMR Spectra

A number of 6-arylmethylideneamino-2H-chromen-2-ones were synthesized by reaction of 6-amino-2H-chromen-2-one with aromatic and heterocyclic aldehydes. A linear relation was revealed between the chemical shifts of the azomethine CH=N proton and protons in the chromene ring, on the one hand, and Hammett constants σ of the para substituents, on the other. Formation of intramolecular hydrogen bond in ortho-hydroxy derivatives induces a downfield shift of signals from protons in positions 3–5, 7, and 8 and CH=N proton (9-H) and upfield shift of the o-H signal (14-H).__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 7, 2005, pp. 1085–1091.Original Russian Text Copyright © 2005 by Ganushchak, Kobrin, Bilaya, Mizyuk.     

Synthesis,Structure, and Keto-Enol Tautomerism of 3-R<Superscript>1</Superscript>-5,5-R<Superscript>2</Superscript>,R<Superscript>2</Superscript>-6-R<Superscript>3</Superscript>-2,3,5,6-Tetrahydropyran-2,4-diones

Ethyl esters of 2,4-dibromo-2-R¹-4-R²-3-oxopentanoic and -hexanoic acids react with zinc and aliphatic or aromatic aldehydes under the conditions of the Reformatskii reaction to give 3-R¹-5,5-R², R²-6-R³-2,3,5,6-tetrahydropyran-2,4-diones, which are obtained in three forms: keto, enol with enolization of the keto group, and enol with enolization of the ester group. The keto form is isolated by crystallization from a mixture of CCl₄ and petroleum ether; the first enol form, from MeOH, EtOH, and polar aprotic solvents; and the second enol form, from CHCl₃. The second enol form is oxidized in DMSO to form a keto compound containing a hydroxy group at the 3-position of the heteroring.     

Kinetics and mechanism of nucleophilic substitution of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II) by pyridine bases

The reaction of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II), Pd(RaaiMe)Cl₂ where RaaiMe = p-R–C₆H₄N=N–C₃H₂N₂-1-Me; R = H(1), Me(2), Cl(3), with pyridine bases [RPY: R = H (a), 4-Me (b), 4-Cl (c), 2-Me (d), 2,6-Me₂ (e), 2,4,6-Me₃ (f)] has been studied spectrophotometrically in MeCN at 451 nm. The products (4) have been isolated and characterised as trans-Pd(RPy)₂Cl₂. The kinetics of the nucleophilic substitution has been examined under pseudo-first-order conditions at 298 K. A single phase reaction step has been observed for bases such as Hpy (a), 4-MePy (b) and 4-ClPy (c) and follows the rate law: rate = (a + k[RPy]²[Pd(RaaiMe)Cl₂]). The bases 2-MePy (d), 2,6-Me₂Py (e) and 2,4,6-Me₃Py (f) exhibits a bi-phasic reaction and follows the rate laws: rate–1 = (a + k[RPy][Pd(RaaiMe)Cl₂]) and rate–2 = (a + k[RPy][Pd(RaaiMe)-Cl₂]), where k is the third-order rate constant; k is the second-order first phase rate constant, k is the second-order second phase rate constant and a/a/a correspond to the solvent dependent constant of the respective reaction path. The rate data supports a nucleophilic association path. External addition of Cl^– (LiCl) suppresses the rate, which follows the order: k/k/k (3) > k/k,k (1) > k/k,k (2). The k values are linearly related to the Hammett constants. The 2-substituted pyridines (d–f) remarkably reduce the rate and show a bi-phasic reaction behaviour as compared with 4-Rpy (a–c). This is attributed to the steric effect that destabilises the transition state. The rate decreases with increasing steric crowding at the ortho-position and follows the order: (d) > (f) > (e). The 4-substituted pyridines control the rate via an inductive effect and follow the order: (b) > (a) > (c).     

Synthesis,characterisation and photocatalytic activity of Ag<Superscript>+</Superscript>- and Sn<Superscript>2+</Superscript>-substituted KSbTeO<Subscript>6</Subscript>

Ag⁺- and Sn²⁺-substituted KSbTeO₆ were prepared by a facile ion-exchange method at ambient temperature. All the samples were characterised by scanning electron microscopy, energy-dispersive spectra, thermogravimetric analysis, powder X-ray diffraction, Raman spectra and UV-VIS diffuse reflectance spectra. Both Sn²⁺- and Ag⁺-substituted KSbTeO₆ were crystallised in a cubic lattice with the \(Fd\bar 3m\) space group. The band-gap energy of all the samples was deduced from their UV-VIS diffuse reflectance spectral profiles. The visible light-induced photocatalytic oxidation of the methylene blue (MB) dye was examined in the presence of all the as-prepared materials. The Ag⁺- and Sn²⁺-substituted KSbTeO₆ exhibited a higher photocatalytic activity than the parent KSbTeO₆ in degradation of the MB dye under visible light irradiation.     

Synthesis and Characterization of 1,3,2‐Bis (arylamino) phospholidine, 2‐oxide Derivatives: Crystal Structures of $\rm Cl(O)\overline{PN(p-Me-C_{6}H_{4})CH_{2}CH_{2}N}(p-Me-C_{6}H_{4})$ and $\rm ((CH_{2}C_{6}H_{5})(O)\overline{PN(p-Me-C_{6}H_{4})CH_{2}CH_{2}N}(p-Me-C_{6}H_{4})$

Using phosphoryl chloride as a substrate, a family of 1,3,2‐bis(arylamino) phospholidine, 2‐oxide of the general formula ; (X=Cl, 6a ; X=NMe₂, 1b ; X=N(CH₂C₆H₅)(CH₃), 2b ; X=NHC(O)C₆H₅, 3b ; X=4Me‐C₆H₄O, 4b ; X=C₆H₅O, 5b ; X=NHC₆H₁₁, 6b ; X=OC₄H₈N, 7b ; X=C₅H₁₀N, 8b ; X=NH₂, 9b ; X=F, 10b and Ar=4Me‐C₆H₄) was prepared and characterized by ¹H, ¹⁹F, ³¹P and ¹³C NMR and IR spectroscopy, and elemental analysis. A general and practical method for the synthesis of these compounds was selected. The structures of 6a and 2b were determined by single‐crystal X‐ray diffraction techniques. The low temperature NMR spectra of 2b revealed the restricted rotation of P‐N bond according to two independent molecules in crystalline lattice.     

Oxidative dehydrogenation of N-(2-hydroxy-3,5-R<Superscript>1</Superscript>,R<Superscript>2</Superscript>-benzyl)-4-aminoantipyrines in the complexation reaction

Reactions of N-(2-hydroxy-3,5-R¹,R²-benzyl)-4-aminoantipyrines with copper acetate in ethanol gave complexes with Schiff bases (SBs) rather than the expected complexes with reduced SBs; i.e., the starting ligands undergo oxidative dehydrogenation during the complexation reaction. The corresponding complexes with reduced SBs were obtained from sodium salts of the ligands and cupric sulfate in aqueous solutions. Kinetic measurements showed that oxidative dehydrogenation occurs in the heteroleptic complexes Cu(L ⁱ )(CH₃COO)(X) (L ⁱ H are derivatives of N-(2-hydroxy-3,5-R¹,R²-benzyl)-4-aminoantipyrines; i = 6–10; X = H₂O, CH₃OH, CH₃CH₂OH) but does not occur in the complexes CH₃OH, CH₃CH₂OH. The absence of oxidative dehydrogenation of the ligands in Cu(L ⁱ )₂ · H₂O can be explained by the octahedral environment of the Cu²⁺ ion and, accordingly, the absence of the coordination site for molecular oxygen. The molecular structures of two Cu(II) complexes with SBs were determined by X-ray diffraction.     

Synthesis and Characterization of New Os<Subscript>2</Subscript><Superscript>5+</Superscript> and Os<Subscript>2</Subscript><Superscript>6+</Superscript> Azido Complexes

Reaction of Os₂(OAc)₄Cl₂ with an excess of HDPhF (HDPhF = N,N′-diphenylformamidine) gives a high yield of Os₂(DPhF)₄Cl₂ (1), which can be converted to its azido analog, Os₂(DPhF)₄(N₃)₂ (3), by treatment with NaN₃. We report a major improvement on the preparation of Os₂(chp)₄Cl (2; Hchp = 2-chloro-6-hydroxypyridine) by synthesizing the compound in the reducing solvent ethanol. Reaction of 2 with NaN₃ affords the azido complex Os₂(chp)₄N₃ (4). Compound 3 has been examined by X-ray crystallography, and has an Os–Os bond distance of 2.45 Å, suggesting a (π*)² ground state for the molecule.     

Use of steric crowding to synthesise ruthenium(II) N(1)-alkyl-2-(arylazo)imidazole isomers. Spectral characterization and redox studies

Complexes of N(1)-methyl- and N(1)-benzyl-2-(dimethylphenylazo)imidazoles with ruthenium(II) have been prepared and characterised by physico-chemical and spectroscopic means. The 7,8-dimethylphenylazo ligands gave four stereoisomers, whereas the 8,9-dimethylphenylazo ligands gave only two. Isomer assignments are made on the basis of i.r. and ¹H-n.m.r. data. Redox studies show the Ru^III/II couple at 0.4–0.5 V (versus s.c.e) for the trans,cis,cis-isomers, whereas the other isomers exhibit higher (0.6–0.7 V) potentials. Two successive azo reductions are observed at negative potentials. The difference between the first metal and ligand redox potentials is linearly correlated with CT [t₂(Ru) ^*(RL)].     

Oximation of 2-(R<Superscript>1</Superscript>-Amino)-4-(R<Superscript>2</Superscript>-imino)naphthalen-1(4<Emphasis Type="Italic">H</Emphasis>)-ones

The oximation of 2-(R¹-amino)-4-(R²-imino)naphthalen-1(4H)-ones with hydroxylamine hydrochloride in pyridine afforded 2-(R-amino)-4-(hydroxyimino)naphthalen-1(4H)-ones.     

Extending a Tandem Mass Spectral Library to Include MS<Superscript>2</Superscript> Spectra of Fragment Ions Produced In-Source and MS<Superscript>n</Superscript> Spectra

Tandem mass spectral library searching is finding increased use as an effective means of determining chemical identity in mass spectrometry-based omics studies. We previously reported on constructing a tandem mass spectral library that includes spectra for multiple precursor ions for each analyte. Here we report our method for expanding this library to include MS² spectra of fragment ions generated during the ionization process (in-source fragment ions) as well as MS³ and MS⁴ spectra. These can assist the chemical identification process. A simple density-based clustering algorithm was used to cluster all significant precursor ions from MS¹ scans for an analyte acquired during an infusion experiment. The MS² spectra associated with these precursor ions were grouped into the same precursor clusters. Subsequently, a new top-down hierarchical divisive clustering algorithm was developed for clustering the spectra from fragmentation of ions in each precursor cluster, including the MS² spectra of the original precursors and of the in-source fragments as well as the MSⁿ spectra. This algorithm starts with all the spectra of one precursor in one cluster and then separates them into sub-clusters of similar spectra based on the fragment patterns. Herein, we describe the algorithms and spectral evaluation methods for extending the library. The new library features were demonstrated by searching the high resolution spectra of E. coli extracts against the extended library, allowing identification of compounds and their in-source fragment ions in a manner that was not possible before.

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