Azomethine Proton Research Articles

Structurally characterized acylruthenium organometallics bearing a pendant aldehyde function

By reacting [Ru(RL1)(PPh3)2(CO)Cl], (1) (R = C6H4Me, Et) with an excess of CNBu t in the presence of NH4PF6, organometallics of the type [Ru(RL2)(PPh3)2(CNBu t )2]PF6, (2) have been isolated in excellent yield [RL1 = C6H2O-2-CHNHR(p)-3-Me-5, RL2 = C6H2(CO)-O-2-CHNHR(p)-3-Me-5]. These organometallics, on controlled hydrolysis, produce [Ru(L3)(PPh3)2(CNBu t )2], (3) in very good yield (L3 = C6H2(CO)-O-CHO-3-Me-5). In both ([2(C6H4Me)] · 2H2O) and ([3] · 2CH2Cl2) the two phosphine ligands lie in trans positions. In ([2(C6H4Me)] · 2H2O) the Ru(C6H4MeL2) fragment, excluding the pendant tolyl ring, is a near perfect plane (mean dev ~ 0.02A) which makes a dihedral angle of 5.2° with the tolyl plane. The acyl chelate ring in ([2(C6H4Me)] · 2H2O) is excellently planar with a mean deviation of 0.006°. In ([3] · 2CH2Cl2) the Ru(L3) fragment defines a crystallographic plane of symmetry, the coordinates of the atom being of the type x, 1/4z. The complex ([2C6H4Me)] · 2H2O) displays N–HȮFO (iminium-phenolato) hydrogen bonding while in ([3] · 2CH2Cl2) C–H...O hydrogen bonding is present. Characteristic spectral data (u.v.–vis, i.r. and 1H n.m.r.) of the complexes are reported. A notable feature is that an allowed band near 500 nm due to the t2g → π*(azomethine) charge transfer transition, which is diagnostic of the coordinated iminium-phenolato function, is present in (3) but this band is absent in the aldehydic acyl complex (2). In the 1H n.m.r. spectrum the N+–H signal in (2) (near 13.5 ppm) is split into a doublet due to transcoupling with the azomethine proton. The aldehydic proton of (3) resonates as a sharp singlet near 10 ppm. In CH2Cl2 solution (2) and (3) display quasireversible a Ru III /Ru II cyclic voltammetric response with E1/2 near 0.9 and 0.5 V versuss.c.e. The conversion (2) → (3) is accompanied by the nucleophilic attack of water. The complex (3) is also obtained directly from (1) by reaction with CNBu t in the presence of H2O. The aldehyde function in (3) is deactivated by the existing acyl moiety; as a result further decarbonylation does not take place.

Synthesis, characterization and study of polymeric iron(III) complexes with bidentate p-hydroxy Schiff bases as heterogeneous catalysts

Abstract The chelating Schiff base ligands 4-(naphthalen-1-yliminomethyl)-phenol ( I ) and 4-(naphthalen-2-yliminomethyl)-phenol ( II ) were obtained by condensation of α- or β-naphthyl amine respectively, with p -hydroxy benzaldehyde. The reaction of the chelating ligands I and II with iron(III)nitrate in aqueous ethanol afforded new coordination polymer complexes poly-[Fe(C 10 H 7 -1-N CH C 6 H 4 4-O) 3 ] ( III ) and poly-[Fe(C 10 H 7 2-N CH C 6 H 4 4-O) 3 ] ( IV ). The Schiff bases and their iron(III) complexes were characterized by various physico-chemical techniques. The chemical formulae of compounds were determined by elemental analyses. It was found that both of these ligands acted as bidentate bridging ligands and thus formed cross-linked hexacoordinated polymeric complexes. The coordination was ascertained from the IR, 1 H NMR and UV–Vis Spectral data of the ligand and complexes wherein, a new weak band at 472 and 466 nm were observed due to symmetry forbidden d–d transitions. The azomethine proton signals in the 1 H NMR spectra of the Schiff bases I and II observed between δ 8.45 and 8.55 ppm were observed upfield shifted in the spectra of the complexes. The catalytic properties of the coordination polymers as heterogeneous catalysts were examined by liquid phase hydroxylation of phenol using H 2 O 2 as an oxidant. It was found that these complexes provide high TOF value for the hydroxylation of phenol by H 2 O 2 . The % phenol conversion was higher with β-Schiff base complex IV but the product distribution was almost the same with either of the complex.

Synthesis, magnetic and special studies of some novel metal complexes of Cu(II), Ni(II), Co(II), Zn[II), Nd(III), Th(IV), and UO2(VI) with schiff bases derived from sulfa drugs, viz., Sulfanilamide/Sulfamerazine and o-vanillin

Keeping in view the chemotherapeutic value of the sulfa-drugs, two scruff base ligands viz ℴ-vanillin-sulfanilamide (ℴVSaH) and ℴorder-vanillin-sulfamerazine (ℴVSmrzH) and their bipositive, tripositive tetrapositive and uranyl metal complexes have been synthesized and characterized by elemental analysis, IR spectra, thermal analysis, magnetic suceptibility measurements, diffuse reflectance spectra and 1H NMR spectra and molar conductance measurements. The disappearance of phenolic proton signal at 12.6 ppm and the upfield shift of azomethine proton rignal (from 8.65 ppm against 8.96 ppm in the ligand) upon complexation indicate the coordination by phenolic oxygen (after deprotonation) and azomethine nitrogen respectively. Zn(II), Th(IV) and UO2(VI). complexes are found to be diamagnetic as expected. The low molar conductance values suggest the non-electrolytic nature of these complexes. The general compositions of there complexes are found to be [M(ℴVSa)2] where M=Cu(II), Ni(II), Zn(II), Co(II), [Nd(ℴVSa)(N03)2(H2O)2] [Th(ℴVSa)(N03)3(H20)] [UO2(ℴVSa)(ℴAc)(H2O)] and [M1(ℴVSmrz)2(H2O)2] where M1=Cu(II), Ni(II), Co(II) and Zn(II) and [UO2(ℴVSmrz)2].

Structure Control of Synthetic Bilayer Membranes from Single-Chain Amphiphiles Containing the Schiff Base Segment. III. Proton NMR Study

The molecular motion in the synthetic bilayer membranes formed from a series of single-chain ammonium amphiphiles with a rigid Schiff base segment, the diphenylazomethine chromophore, has been investigated via the use of1H NMR spectroscopy. The changes in chemical shift of the azomethine protons suggest the effect of conformation and aggregation variation during the bilayer formation process, which confirms the concept of conformation control of the supramolecular systems containing a nonplanar chromophore.

Vitamin B‐6 model reactions. Part VI‐a Hammett relationship for the magnitude of pseudoallylic proton‐proton spin coupling constants in substituted azomethines

AbstractFour‐bond proton‐proton spin coupling constants were measured between the azomethine proton and the glycine CH protons of some coordinated glycine Schiff bases where the parent aldehyde is aromatic. Such systems are models for vitamin B6 enzyme substrate complexes. It is demonstrated that the coupling constants are not only related to the dihedral angles between coupled systems but they are also linearly related to the Hammett σ value of the substituents on the aromatic ring. A method is suggested for the calculation of dihedral angles between proton‐carbon bonds in these pseudoallylic systems.

Synthesis, chiroptical and electrochemical studies of dioxouranium(VI) complexes of aldimine derivatives ofL-/D-histidine and crystal structure of (2,2′-bipyridyl)dioxo(N-o-vanillylidene-L-histidinato)uranium(VI)–water–methanol(1/1/1)

A series of new dioxouranium(VI) complexes has been synthesised using N-(salicylidene)-L-histidine (H2sal-Lhis) and N-(o-vanillylidene)-L-histidine (H2van-L-his) and the corresponding D-histidines. They have been characterized by elemental analyses and physicochemical studies. The crystal and molecular structures of [UO2(van-L-his)(bipy)]·MeOH·H2O (bipy = 2,2′-bipyridine) have been determined by X-ray crystallography. The aldimine ligand in this compound is tridentate. The methanol and water molecules are hydrogen bonded to each other and the water molecule to the carboxylate O atom. The diamagnetic UO22+ entity serves as a chiroptical probe, undergoing stereospecific complex formation with the aldimine ligands. as well as for the interpretation of their 1H NMR spectra, which in conjunction with two-dimensional NMR spectra, reveal the different spin-spin interactions, including the long range one between the azomethine (CHN) and Hα proton of the amino acid residue. The CD and NMR spectral data of the quasi-enantiomorphous UO22+ complexes containing the L-/D-amino acid residues have helped to ascertain the conformational differences between each such pair; these differences can modulate energies of the half-filled highest occupied molecular orbitals in different ways. As these orbitals are involved in the electron-transfer process, the relevant complexes respond differently when subjected to cyclic voltammetry.

Generation of Radical Anions of Nifurtimox and Related Nitrofuran Compounds By Ascorbate

Nifurtimox analogues bearing triazol-4-yl, benzimidazol-1-yl, triazin-4-yl or related groups as counterpart of the (5-nitro-2-furfurylidene) amino group were reduced to their nitro anion radicals by ascorbate in anaerobic solutions at high pH. The ESR spectra of the radical anions showed hyperfine spin couplings restricted to the nitrofuran moiety. With these compounds, the spin density at the nitro group was greater than with nifurtimox, nitrofurazone and nitrofurantoin. At neutral pH, solutions containing ascorbate and nitrofuran derivatives consumed oxygen, the compounds bearing unsaturated nitrogen heterocycles being the most effective. Superoxide dismutase and catalase decreased the rate of oxygen consumption, thus demonstrating the production of superoxide and hydrogen peroxide, respectively. NMR spectra of the triazol-4-yl and triazin-4-yl nitrofuran derivatives showed a deshielding effect for the azomethine proton, which was undetectable with nifurtimox and nitrofurazone.

Conformational analysis of MBBA fluorinated analogues by 1H and 13C - NMR

1H- 13C -chemical shifts correlation analysis for MBBA and a series of its fluorinated analogues have been carried out. The azomethine proton chemical shift is shown to be sensitive to the aniline ring torsion angle and can be used for its approximate estimation.

Substituent Effects of the1H and13C NMR Spectra of Substituted o-Hydroxyaromatic Schiff Basies (N-Salioylideneanilines and N-Benzylidene-2-Aminophenols)

Abstract 1H and 13C NMR spectra of para-substituted o-HOC6H4 CH[dbnd]NC 6H4 X and YC6H4 CH[dbnd]NC 6H4OH-o were determined in CDC13. Reasonable correlations between the azomethine proton and 13C chemical shifts and Hammett's σP constants were obtained. The observed through-resonance effect was attributed to intramolecular hydrogen bonding between the hydrogen at the phenolic group and the imine nitrogen in the molecule.

Dioxomolybdenum(VI) complex with N, N′- ethylenebis(salicylideneimine)

The interaction of N, N′-ethylenebis(salicylideneimine), H 2salen, with ammonium molybdate yielded the molybdenum(VI) complex MoO 2(salen) with the cis-dioxostructure as inferred from IR spectral studies. The 1H NMR chemical shifts of azomethine protons in the free ligand and the complex are 8.14 and 8.39 δ, respectively, suggesting the bonding of the azomethine nitrogen to MoO 2 group. The thermal decomposition behaviour of the complex is discussed.

1H- and13C-NMR spectra of platinum(II) complexes ofSchiff bases with acis-(N2O2)-donorset in comparison to nickel(II) and organocobalt(III) complexes

The1H- and13C-NMR spectra of platinum(II), nickel(II), and ethylcobalt(III)Schiff base complexes of type 1 are reported. The platinum complexes show spin-spin coupling between platinum and the azomethine protons. While the platinum and cobalt complexes show upfield shifting of their13C resonances relative to the nickel complexes, the ethylcobalt complex1 b is characterized by highfield shifting of several13C resonances. Structural and electronic arguments explain this behaviour. The influence of the peripheral substituents on the shifting of13C resonances is related to the possibility of forming macrocyclic derivatives.

Substituent Effects on Azomethine Proton Chemical Shifts and 13C–H Coupling Constants in N-Benzylideneanilines. Generality of Inverse Substituent Effects on the Azomethine Proton Chemical Shifts

Abstract Azomethine proton chemical shifts were measured for series of N-benzylideneanilines; C6H5CH=NC6H4X-4, 4-YC6H4CH=NC6H5, 4-NMe2C6H4CH=NC6H4X-4, 4-YC6H4CH=NC6H4NMe2-4, 4-NO2C6H4CH=NC6H4X-4, 4-YC6H4CH=NC6H4NO2-4, and 4-YC6H4CH=NC6H3(CH3)2-2,6. It was found that for N-benzylideneanilines carrying the variable substituents X on the anilino benzene ring the azomethine protons undergo upfield shifts with increasing electron-withdrawing property of X, whereas those for N-benzylideneanilines carrying the variable substituents Y on the benzylidene benzene ring exhibited expected lowfield shifts with increasing electron-withdrawing property of Y. 13C–H coupling constants for azomethine carbon–hydrogen bonds (J(13C–H)) were also measured for several derivatives of 4-NO2C6H4CH=NC6H4X-4, 4-YC6H4CH=NC6H4NO2-4, and 4-YC6H4CH=NC6H3(CH3)2-2,6. In contrast with the substituent effects on the azomethine proton chemical shifts, the coupling constant increases with increasing electron-withdrawing property of the substituent X or Y, regardless of the position of the substituents, indicating that a through-bond electronic effect of the substituent is a predominant factor to determine the magnitude of the coupling constant. These results show that the anomalous substituent effects on the azomethine proton chemical shifts are a general phenomenon in N-benzylideneanilines which carry variable substituents on the anilino benzene ring, and support our previous proposition that the anomaly is likely to originate primarily from the change of molecular conformation of these N-benzylideneanilines in solution.

A New Aspect on the Origin of an Anomalous Substituent Effect on the Azomethine Proton Chemical Shifts in 4-Substituted N-Benzylideneanilines

Abstract Carbon-13 chemical shifts, azomethine proton chemical shifts, and azomethine carbon–hydrogen coupling constants have been determined for N-benzylideneaniline and its several derivatives bearing o-methyl and/or p-nitro groups on the aromatic ring on the nitrogen atom (ring A). The anomalous upfield shift of the azomethine proton caused by introduction of a 4-nitro group on the ring A can be attributed to the increase in the twist angle θN of the ring A from the molecular plane containing the C=N bond.

Investigation of substituent effects on the 1H and 13C NMR spectra of (Z)‐N‐(arylmethylene)‐arylamine N‐oxides (α,N‐diaryl nitrones)

AbstractSubstituent effects on the 1H and 13C chemical shifts of 18 differently substituted (Z)‐α,N‐diaryl nitrones [N‐(p‐X‐benzylidene)phenylamine N‐oxides (Series I) and N‐(benzylidene)‐p‐Y‐phenylamine N‐oxides (Series II)] have been obtained. A correlation has been found between the chemical shifts of the azomethine proton (H‐α) and the Hammett σ parameters and the Swain and Lupton F and R parameters. Correlations of the chemical shifts of C‐1 and C‐4′ in Series I, and of C‐α and C‐1′ in Series II, with the same parameters have been investigated. In addition, the chemical shifts of the aromatic protons and carbons of the p‐disubstituted (m‐disubstituted in one case) benzene rings correlated with the appropriate substituent increments (Zi). These correlations confirm the dual behaviour of the nitrone group and the presence of through‐resonance in these nitrones.

Proton nmr studies of smectic phases of three n-(4-n-alkyloxybenzylidene)-4'-n-alkylanilines (n0 . m's)

Proton NMR studies of the liquid crystals 50.6, 70.5, and 70.6 are presented. In all mesophases there is a clear proportionality between dipolar doublet splittings of the proton NMR spectra and the corresponding second moments indicating that the motions giving rise to the observed lineshapes remain fast on the NMR time cale even in the highly-ordered smectic-G phases and that no essential conformational changes occur. From the angular dependences of the lineshapes and second moments it could be concluded that the preferred direction of the sample, once aligned by the strong magnetic field in smectic-A, is preserved through all smectic phases though there are several changes from untilted to tilted phases. From linewidth measurements at the magic-angle orientation, activation energies for a thermally activated motional process could be derived in the low-temperature smectic phases (B, F, G) which differ for B- and F/G-phases, respectively. Simulations of the proton NMR lineshape confirm the existence of a twist of the aniline ring against the benzaldehyde-azomethine group plane as suggested by quantum-chemical considerations and X-ray investigations of related compounds. Besides one has to assume an additional motion decoupling the dipolar interaction between the azomethine proton and the protons of the neighbouring ring Observation d'une remarquable proportionnalite entre les decompositions dipolaires du profil de raie et le deuxieme moment correspondant, indiquant que les mouvements qui controlent les profils de raie observes restent rapides et qu'il n'y a pas de changements de conformation essentiels

Asymmetric Synthesis of α-Deuterated α-Amino Acids through Nonenzymatic Transamination Reaction and the Determination of Their Enantiomeric Excesses

Abstract Optically active α-deuterated α-amino acids were prepared in methano-d through Zn2+-catalyzed transamination reaction between the chiral pyridoxamine analogs, (R)- or (S)-15-aminomethyl-14-hydroxy-5,5-dimethyl-2,8-dithia[9] (2,5)pyridinophane and various α-keto acids with enantiomeric excesses ranging from 40 to 94%. Aliphatic α-keto acids gave α-deuterated α-amino acids, whereas aromatic ones possessing a methylene group between the carbonyl group (ketone) and the aromatic ring underwent concomitant deuterium substitution at the active methylene group to give the amino acids deuterated at both α- and β-positions of the carboxyl group. The use of the (S)-pyridoxamine analog gave the (R)-deuterated α-amino acids in excess and vice versa. The enatiomeric excesses of the amino acids were determined through the analyses of 1H NMR spectra of the Schiff bases produced by the condensation of the amino acids with the chiral pyridoxal analog, (R)- or (S)-15-formyl-14-hydroxy-2,8-dithia[9](2, 5)pyridinophane. The azomethine protons of the diastereomeric Schiff bases were clearly resolved in the spectrum and their intensities well reflected the amount of the diastereomers.

Ruthenium complexes with diazadienes. I. Synthesis and crystal structure ofcis-Ru(dad)2Cl2 (dad = 2,7-dimethyl-3,6-diaza-3,5-octadiene)

Reduction of RuCl3 · 3 H2O in the presence of the title diazadiene i-PrN=CH-CH=NPr-i (from the condensation of glyoxal and isopropylamine) gives the intensely colouredcis-Ru(dad)2Cl2 (2) in moderate yield. The crystal and molecular structure was determined by x-ray diffraction. Complex (2) crystallizes in space group P ¯1 witha = 1110.2(10),b = 1360.3(6) andc = 1427.6(8) pm;a = 85.05(4), β = 79.07(6) and γ=82.65(6)° with four molecules in the unit cell. Electronic and1H n.m.r. spectra are discussed. An abnormally small vicinal coupling of the azomethine protons is detected.

The Mechanism of the Spin-Spin Coupling of Dimethyllead(IV) Complexes with ONNO Quadridentate Schiff Base Ligands and the Magnetically Non-equivalent Methyl Protons of a Dimethyllead(IV) Complex

Abstract Several dimethyllead(IV) complexes with ONNO quadridentate Schiff base ligands have been prepared. The spin-spin couplings between the lead nucleus and the azomethine proton of the ligands, 3J(207Pb–N=CH), as well as the lead-methyl proton couplings, 2J(207Pb–CH3), have been observed in various solvents. Both J values inclease with an increase in donor strength of the solvents. The mean excitation energy, the ΔE term in the Fermi contact term plays a dominating role for the lead-proton spin-spin coupling constants. Two methyl proton signals were, for the first time, found to be magnetically non-equivalent in the dimethyllead(IV) complex of sapr.

Azomethine proton chemical shift of Schiff bases

Abstract The azomethine proton chemical shift of thirteen para-substituted neutral Schiff bases, XC 6 H 4 CHNC 6 H 4 Y, has been determined in DMSO. Excellent correlation of the chemical shifts of azomethine group with Hammet σ p constants was obtained for substituents in the benzaldehyde moiety. The lack of correlation for substituents in the aniline ring was attributed to the non-planar structure of the benzalaniline derivatives.

Mass spectra and fragmentation patterns of malonaldehydedianil and some of its metal complexes

AbstractUnder electron impact malonaldehydedianil and its bis Co(II), Ni(II) and Zn(II) complexes produce a stable molecular ion. The Cu(II) complex appears to decompose prior to ionization. The free dianil molecular ion fragments by expulsion of the azomethine proton or by fission of C‐N bonds. The molecular ions of the metal complexes usually expel a complete ligand before undergoing demetallation.