Ruthenium-mediated Selective Aromatic Thiolation in the Complex [RuII{o-S—C6H4-(p-R-)—N=N—C3H2NN(1)—R′}2]. Synthesis, Spectroscopic, e.p.r., Electro-chemical Characterization and Spectro-electrochemical Correlation

The reaction of ctc-[Ru(RaaiR′)₂Cl₂] (3a–3i) [RaaiR′=1-alkyl-2-(arylazo)imidazole, p-R—C₆H₄—N=N— C₃H₂NN(1)—R′, R=H, OMe, NO₂, R′=Me, Et, Bz] with KS₂COR′′ (R′′=Me, Et, Pr, Bu or CH₂Ph) in boiling dimethylformamide afforded [Ru^II{o-S—C₆H₄(p-R-)—N=N—C₃H₂NN(1)—R′}₂] (4a–4i), where the ortho-carbon atom of the pendant phenyl ring of both ligands has been selectively and directedly thiolated. The newly formed tridentate thiolate ligands are bound in a meridional fashion. The solution electronic spectra exhibit a strong MLCT band near 700 nm and near 550 nm, respectively in DCM. The molecular geometry of the complexes in solution has been determined by H n.m.r. spectroscopy. Cyclic voltammograms show a Ru(II)/Ru(III) couple near 0.4 V and an irreversible oxidation response near 1.0 V due to oxidation of the coordinated thiol group, along with two successive reversible ligand reductions in the range −0.80–0.87 V (one electron), −1.38–1.42 V (one electron). Coulometric oxidation of the complexes at 0.6 V versus SCE in CH₂Cl₂ produced an unstable Ru(III) congener. When R=Me the presence of trivalent ruthenium was proved by a rhombic e.p.r. spectrum having g₁=2.349, g₂=2.310.     

The deexcitation of the S1 state of aminoanthraquinones: A steadystate and timeresolved study

The non-radiative processes of deactivation from the lowest singlet excited state of aminoanthraquinones have been studied using steady-state and time-resolved methods. The fluorescence decay rate constant, k_f correlates well with the solvent polarity parameter, E_T(30), in nonhydrogen bonding solvents. Large deuterium isotope effects in fluorescence lifetimes (τ_f) and quantum yields (ϕ_f) are observed in the case of 1-amino (AAQ) and 1-methylaminoanthraquinones (MAQ), where the S₁ state is mainly deactivated through internal conversion to the ground state. The temperature-dependence of the fluorescence quantum yields of various aminoanthraquinones was also investigated. The ϕ_f and τ_f exhibited strong temperature-dependence in the case of 1-acetylaminoanthraquinone (ACAQ). In the case of ACAQ, the intersystem crossing to the triplet state is a major deactivation channel from the S₁ and in this derivative a close-lying T₂ state seems to be responsible for the high k_isc rate. The fluorescence properties of 1,5-diaminoanthraquinone (DAQ) are affected by intermolecular hydrogen bonding with alcohols. Increasingn-alkyl chain length in the case of l-(n-alkyl)aminoanthraquinones from methyl to butyl does not produce any change in the fluorescence properties, whereas a hydroxypropyl substitution results in a small decrease of ϕ_f and τ_f in these compounds, indicating an interaction of the hydroxyl group with the carbonyl group of the aminoanthraquinones.     

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.     

IR multiphoton dissociation of CF3I. Pressure effect with inert and reactive gases

The IR multiphoton dissociation of CF₃I has been studied in the presence of isobutane and with isobutane and Ar and CO₂ as inert gases. The dependence of the reaction probability P(Φ) with fluence (ϕ) is confirmed. Modeling of the experimental results shows that for the energy transfer processes the average energy transferred per collision 〈†E〉_d varies with (ϕ).     

Synthesis and study of organosilicon hydroxymethylated phenols

A series of (hydroxymethyl)hydroxyphenyldimethylsiloxanes of linear and branched structures were synthesized by the reaction with formaldehyde in aqueous alkaline medium of organosilicon phenols of general formula R′[Si(CH₃)₂O] _n [Si(CH₃)RO] _m SiMe₂R′, where R′ was 4-hydroxy-3-methoxyphenylpropyl, R was methyl or 4-hydroxy-3-methoxyphenylpropyl. The structure and composition of the siloxanes were confirmed by elemental analysis, NMR and IR spectroscopy. The homocondensation of (hydroxymethyl)hydroxyphenyldimethylsiloxanes at the hydroxymethyl groups was investigated. A possibility of reaction of (hydroxymethyl) hydroxyphenyldimethylsiloxanes with phenol-formaldehyde resin to form copolymers was demonstrated.     

1H and13C NMR study of tin-containing sulfoxide, sulfimide, and sulfoximide

Sulfoxide RS(O)R′ (1), sulfimide RS(=NSO₂Ar)R′ (2), and sulfoximide RS(O)(=NSO₂Ar)R′ (3) (R=Me₃Sn(CH₂)₃, R′=n-C₅H₁₁, Ar=4-C₆H₄Cl) were investigated by¹H and¹³C NMR spectroscopy. Unlike 3, compounds 1 and 2 have a cyclic structure due to the intramolecular donor-acceptor S→Sn interaction. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1966–1969, November, 1997.     

Kinetic and mechanistic studies of the interaction of 2-mercapto pyridine with dichloro[1-alkyl-2-(arylazo)imidazole]palladium(II) complexes

Nucleophilic substitution of Pd(RaaiR′)Cl₂ [(RaaiR′ = 1-alkyl-2-(arylazo)imidazole, p-R-C₆H₄-N=N-C₃H₂NN-1-R′; where R = H(a)/ Me(b)/ Cl(c) and R′ = Et(1)/Bz(2)] with 2-Mercaptopyridine (2-SH-Py) in acetonitrile (MeCN) at 298 K, to form [Pd₂(2-S-Py)₄], has been studied spectrophotometrically under pseudo-first-order conditions and the analyses support the nucleophilic association path. The reaction follows the rate law, Rate = {k ₀ + k [2-SH-Py] ₀ ² }[Pd(RaaiR′)Cl₂]: first order in Pd(RaaiR′)Cl₂ and second order in 2-SH-Py. The rate of the reaction follows the order: Pd(RaaiEt)Cl₂ (1) < Pd(RaaiBz)Cl₂ (2) and Pd(MeaaiR′)Cl₂ (b) < Pd(HaaiR′)Cl₂ (a) < Pd(ClaaiR′)Cl₂ (c). External addition of Cl⁻ (LiCl) and HCl suppresses the rate (Rate ∝ 1/[Cl⁻]₀ & ∝1/[HCl]₀). The reactions have been studied at different temperatures (293–308 K) and activation parameters (Δ^‡ H° and Δ ^‡ S°) of the reactions were calculated from the Eyring plot and support the proposed mechanism.     

Synthesis,Spectra and Electrochemistry of Dinitro-bis-{1-alkyl-2-(arylazo) imidazole} Ruthenium(II). Nitro-nitroso Derivatives and Reactivity of the Electrophilic {Ru-NO}<Superscript>6</Superscript>System

Ag⁺ assisted aquation of blue cis-trans-cis-RuCl₂(RaaiR′)₂ (4–6) leads to the synthesis of solvento species, blue-violet cis-trans-cis-[Ru(OH₂)₂(RaaiR′)₂](ClO₄)₂ [Raai R′=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), OMe (b), NO₂ (c) and R′ = Me (1/4/7/10), CH₂CH₃ (2/5/8/11), CH₂Ph (3/6/9/12)] that have been reacted with NO₂⁻in warm EtOH resulting in violet dinitro complexes of the type, Ru(NO₂)₂(RaaiR′)₂ (7–9). The nitrite complexes are useful synthons of electrophilic nitrosyls, and on triturating the compounds, (7b–9b) with conc. HClO₄ nitro-nitrosyl derivatives, [Ru(NO₂)(NO)(OMeaaiR′)₂](ClO₄)₂ (10b–12b) are isolated. The solution structure and stereoretentive transformation in each step have been established from ¹H n.m.r. results. All the complexes exhibit strong MLCT transitions in the visible region. They are redox active and display one metal-centred oxidation and successive ligand-based reductions. The redox potentials of Ru(III)/Ru(II) (E_1/2^M) of (10b–12b) are anodically shifted by ∼ ∼0.2 V as compared to those of dinitro precursors, (7b–9b). The ν(NO) >1900 cm⁻¹ strongly suggests the presence of linear Ru–NO bonding. The electrophilic behaviour of metal bound nitrosyl has been proved in one case (12b) by reacting with a bicyclic ketone, camphor, containing an active methylene group and an arylhydrazone with an active methine group, and the heteroleptic tris chelates thus formed have been characterised.     

Sodium and silver phosphate glasses doped with chlorides of Fe,Mn and Zn

A number of samples of sodium and silver phosphate glasses doped with various compositions of some transition metals viz. iron, manganese and zinc chlorides alongwith undoped samples of sodium and silver phosphate glasses were synthesized and characterized by X-ray diffraction, IR spectral, electrical conductivity and differential scanning calorimetry (DSC). The glass transition temperature (T _g) and crystallization temperature (T _c) values obtained from DSC curves were found to increase with increasing concentration of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses and the following sequence is observed: T _g(–FeCl₃)>T _g(–MnCl₂)>T _g(–ZnCl₂) T _c(–FeCl₃)>T _c(–MnCl₂)>T _c(–ZnCl₂) The increase in T _g and T _c values indicate enhanced chemical durability of the doped glasses. The electrical conductivity values and the results of FTIR spectral studies have been correlated with the structural changes in the glass matrix by the addition of different transition metal cations as dopants.     

A novel series of gold(III)-bis-triphenylphosphine-arylazoimidazole complexes: synthesis and spectroscopic and redox study

Reaction of [Au(PPh₃)₂(tht)₂](OSO₂CF₃)₃ with RaaiR′ in CH₂Cl₂ medium following ligand addition leads to [Au(PPh₃)₂(RaaiR′)](OTf)₃ [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), PPh₃ is triphenylphosphine, OSO₂CF₃ is the triflate anion, tht is tetrahydrothiophen]. The maximum molecular peak of the corresponding molecule is observed in the ESI mass spectrum. The ¹H-nmr spectral measurements suggest methylene, –CH₂–, in RaaiEt gives a complex AB type multiplet while in RaaiCH₂Ph it shows AB type quartets. ¹³C-nmr spectrum suggests the molecular skeleton. In the ¹H–¹H COSY spectrum as well as contour peaks in the ¹H–¹³C heteronuclear multiple-quantum coherence (HMQC) spectrum assign the solution structure. Electrochemistry assign ligand reduction part rather than metal oxidation.     

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.     

An efficient and convenient protocol for the synthesis of novel 1′H-spiro[isoindoline-1,2′-quinazoline]-3,4′(3′H)-dione derivatives

Abstract  An efficient and direct procedure for the synthesis of novel spiro[isoindoline-1,2′-quinazoline]-3,4′(3′H)-dione derivatives is described. The process employs a condensation reaction of 2-aminobenzamides and isatins in the presence of a catalytic amount of KAl(SO₄)₂.12H₂O (alum) in ethanol under reflux. Graphical Abstract        

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.     

New complexes of fullerences C60 and C70 with CoII and MnII tetraphenylporphyrinates and their ESR study

Complexes of fullerenes C₆₀ and C₇₀ with cobalt(II) and manganese(II) tetraphenylporphyrinates of compositions Mn(TPP)·(C₆₀)₂(CS₂)_1.5 (1), Mn(TPP)·C₇₀(CS₂) _x , wherex<=1.25 (2), Co(TPP)·C₆₀(CS₂)_0.5 (3), and Co(TPP)·C₇₀(CS₂) _x , wherex<0.25 (4), were synthesized and studied by ESR spectroscopy. At 77 K, complexes1 and2 have singlet ESR spectra characteristic of the low-spin (S=1/2) state of Mn^II, withg=2.002 and linewidths of 250 G and 300 G, respectively, and differing significantly from that of the initial Mn^II(TPP) (g ₁=5.9 andg=2.0,S=5/2). The spectra of complexes1 and2 exposed to oxygen exhibit hyperfine structure due to interaction with⁵⁵Mn and¹⁴N nuclei. The ESR spectra of complexes3 and4 are asymmetric (<g>=2.4, ΔH _pp=(500–600) G), which is due to the overlap of parallel and perpendicular spectral components. The absence of ESR signals from C₆₀ ^.− and C₇₀ ^.− radical anions makes it possible to conclude that the formation of complexes1–4 is not accompanied by electron transfer from Co(TPP) and Mn(TPP) to fullerences C₆₀ and C₇₀. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 722–725, April, 1999.     

Synthesis of natural triisopentenylated flavanone, euchrenone a2

Euchrenone a₂ (7) isolated from the roots ofEuchresta japonica has been synthesised from 3-prenylphloroacetophenone (1) by other workers. We carried out its cyclodehydrogenation with dichloro dicyano quinone (DDQ) to obtain 6-acetyl-5,7-dihydroxy-2,2-dimethylchromene (2) which was ethoxymethylated in the 7-position to give 6-acetyl-7-ethoxymethoxy-5-hydroxychromene (3). Chalcone condensation of3 and 4-ethoxymethoxy-3-C-prenylbenzaldehyde (4) gave 4,6′-bisethoxymethoxy-2′-hydroxy-6″, 6″-dimethyl-3-C-prenylpyrano (2″, 3″–4,3) chalcone (5) which cyclised with methanolic sodium acetate to give protected 5,4′-bisethoxymethoxy-6″, 6″-dimethyl-3′-C-prenylpyrano (2″, 3″–7,8) flavanone (6). Deprotection of6 with 4% methanolic HCl yielded (7) with melting point and spectral data identical to that of the natural compound.     

Frontier orbital interactions of electron pushing and drawing substituents with ferrocenyl group

The frontier orbital interactions of electron pushing and drawing substituents with ferrocenyl group were analyzed based on the electrochemical,UV visible spectral and spectroelectrochemical results of five ferrocene derivatives,R-Fc-A1(PⅠ),A1-Fc-A1(PⅡ),D-Fc-R (PⅢ),D-Kc-A1(PIV) and D-Fc-A2(PV)(R,CH2OH;A1 CHO;A2,CH=C(CN)2 and D,(C18H37)2N-C6H4-CH=CH) It was found that there are strong interactions of the LUMO (πA) of electron drawing substituents with le2g(dxy,dx2 y2)and e2u of the ferroeenyl group because the energy levels of πA and e2g,C2U of (Cp )2 are close,which lower not only the energy levels of bonded orbits,πA+ and dx2-y2+[πA] of PⅠ,PⅡ,PⅣ and PⅤobviously,but also those of their non-bonded orbu dxy For PⅢ,PⅣ and PⅤ,there are strong interactions of HOMO(πD) of the electron pushing substituent with le of the ferrocenyl group because the levels of πD and e of (Cp)2 are close,which result in the formation of anti-bonded orbit,πD- and bonded orbit     

Post-column photochemical reaction detection in liquid chromatography based on photosensitized generation of singlet molecular oxygen: Study of reaction parameters and application to the determination of polychlorinated biphenyls

Summary The parameters effecting the sensitivity and selectivity of a photochemical reaction detection scheme based on the reaction of 3-substituted pyrroles with singlet molecular oxygen (¹O₂) in HPLC are reported. Polychlorinated biphenyls (PCBs) were chosen as model compounds for the detection scheme. Following separation by reverse-phase chromatography, PCBs are excited by a Hg pen-ray lamp in a crocheted PTFE photochemical reactor. PCBs that are efficient¹O₂-sensitizers promote ground state O₂ (³Σ_-3) to an excited state (¹Σ_g+ or¹Δ_g) which rapidly oxidizes 3-substituted pyrroles which are added to the mobile phase. Detection is based on the loss of pyrrole. The reaction is catalytic in nature since one analyte molecule may absorb light many times, producing large amounts of¹O₂. Detection limits for 4,4′-dichlorobiphenyl and Aroclors 1242, 1248 and 1254 were improved by 1–2 orders of magnitude over optimized UV-absorbance detection. Configuration of the photochemical reactor and judicious choice of the wavelength used to follow the loss of pyrrole were determined to be the most important factors in terms of sensitivity of the detection scheme. Comparison of three reagents (i.e. 3-substituted-pyrroles) used for trapping¹O₂ demonstrates the effect of substitution on sensitivity and to some extent selectivity of PCB determination.     

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.     

Azoimidazole Complexes of Manganese(II)-thiocyanate. X-ray Structures of 2-(p-tolylazo)imidazole and Bis-[1-methyl-2-(p-tolylazo)imidazole]- Di-thiocyanato-manganese(II)

The reaction of Mn(OAc)₂ · 4H₂O and 1-alkyl-2-(arylazo)imidazole [RaaiR′ where R = H (a), Me (b); R′ = Me (1/3/), Et (2/4/)] and NH₄NCS in MeOH in a 1:2:2 mole ratio afforded [Mn(RaaiR′)₂(NCS)₂] (3) and (4) complexes. They were characterized by different physicochemical methods and the structure has been confirmed by single crystal X-ray diffraction study for title compound. One of the primary ligands was also characterised by an X-ray diffraction study.     

Pre-organization of diarylideneacetonyl crownophanes in single crystals to photochemical transformations

Specific features of crystal packings and pre-organization of diarylideneacetonyl crownophane molecules to solid-phase photochemical transformations were studied on the basis of X-ray diffraction data using methods of simulation of molecular crystal packings. The tendency of the most part of the synthesized macrocyclic E,E-isomers to the formation of homochiral crystals (P2₁2₁2₁) was revealed, while (23E,26E)-11,12,14,15-tetrahydro-8H-dinaphtho-[2,1-k:1′,2′-r][1,4,7,10]tetraoxacyclononadecine-23,26-dien-25(9H)-one is prone to polymorphism. A phenomenon of solid-phase stereospecific photochemical dimerization of molecules according to the syn-head-to-tail type without crystal destruction (single crystal—single crystal transformation) was found for one of the modifications of this crownophane.