Salicylidene Schiff bases

Intensive investigations have been conducted to elucidate the nature of the mechanism of thermochromism of salicylidene Schiff bases. Different techniques or methods suitable for the study of the tautomeric equilibrium between the end form and the (Z)-keto form have been used, including X-ray diffraction, NMR, infrared (IR) and Raman spectroscopy, and theoretical calculations. In the anil-... 

Of the number of chromophoric derivatives of chiral amines for potential use in the establishment of their absolute configuration by BCD measurement only a few have proven to be generally useful. Of these, intensive investigation of the Af-salicylidene (Schiff base) derivatives of chiral primary amines, including unsubstituted and ring-substituted a- and S-arylalkylamines, a-amino acids, unsaturated and satnrated aliphatic and alicyclic amines, and amino sugars, has resulted in the formulation of the salicylidenamino chirality rule ° °. The application of this rule has recently been reviewed and has been successfully used for the establishment of absolute configuration of chiral primary amines in connection with other stereochemical studies. In related studies, the conformations of a series of pyridoxyl-L-a-amino acid Schiff bases were deduced from their CD spectra ... 

Formation of the adduct with dirhodium complex [6] has significantly changed the chemical shift of the compounds in which proton transfer occurred, for example, for the adduct of iV-(5-nitrosalicylidene)-2-ami nobutane, the chemical shift was —198.2, which was shielded by of 110 ppm in comparison to that in the starting Schiff base.12 The large signal shift was due to the shift of the proton transfer equilibrium towards NH tautomer. For the adduct of N-(salicylidene)-2-aminobutane, existing in the OH-form, the 15N chemical shift has changed from —87.5 to — 84.6 ppm. 

Neomycin is insufficiently volatile for direct mass spectrometric analysis. To overcome this problem Inouye- - prepared the volatile N-salicylidene Schiff s base, the M.S. of which, however, did not exhibit a peak for the molecular ion. To observe the molecular ion it was necessary to use the o-trimethylsilyl ether of the N-salicylidene Schiff s base. The spectrum of N-salicylidene neomycin was found to be dependant on the ion-chamber temperature indicating that thermal decomposition plays a significant part in the fragmentation process. 

Ti(OPr )4 reacts with the Schiff bases acetylacetone, 2-hydroxylalkyIimines, and N-[(3-hydroxy-2-naphthyl)methylene]-2-hydroxylalkylimines (H L) in a 1 1 or 1 2 molar ratio to give [TiL(OPr )2] and [TiLj], respectively. Similarly, TKOR) (R = Et or Bu ) react with Af-salicylidene-2-hydroxyethyl-amine (H2L ) to form [TiL (OR)2] or [TiLa]. Treatment of [TiLHOEt)2] with MeOH gives [TiL OMelj] and both these alkoxides appear to have the dimeric structure (16), whereas [TiL (OBu )] and TiLj are monomeric. ... 

The kinetics of hydrolysis of N-salicylidene-2-aminothiazole (119 = HL) have been studied in aqueous 5% methanol in the presence and absence of Co11, Ni, Cu11 and Zn11.408 The solvent deuterium isotope effect on the rate of spontaneous and hydroxide-catalyzed hydrolysis of the Schiff-base anion (L ) is consistent with intramolecular catalysis by the phenoxide ion. Only... 

Schiff bases derived from an aminopyridine and an aromatic aldehyde find use in the spectrophotometric determination of metal ions. For example, iV,iV -bis(salicylidene)-2,3-pyridinediamine 23 has been used in the determination of copper(ll) ions. An advantage of Schiff bases derived from aminopyridines as analytical reagents lies in the simplicity of their preparative procedures <2000CCA81>. 

Low values of v(V=0) indicate polymeric structures in the solid state for oxo-vanadium(iv) chelates with the quadridentate Schiff bases NN-bis(salicylidene)-propane-1,3-diamine, its 3-methyl and 3-isopropyl derivatives, and bis(salicylidene)-(SM 4-Vbutane-1,3-diamine, (Sal)2f+)tnMe. Dissociation occurs in non-donor solvents and in donor solvents to give five- and six-co-ordinate monomers.428 The c.d. spectrum of VO(Sal)2(+)tnMe shows that a configurational effect contributes to... 

Monooxoruthenium(V) complexes of Schiff base ligand [Ru(O) (saloph)X]n+ [saloph = iV,AT-bis(salicylidene)-o-phenylene-diaminato- X = Cl, imidazole, or 2-Me-Im] (143) and [Ru(edtaXO)] (144) have also been claimed by Khan and co-workers, but further characterization of these species is required. 

Mn2 (0)2(02)(Me3tacn)2] +, and [Mn2 0(E)2] with a Schiff-base pentadentate monoanionic ligand (F = N,N-bis(2-pyridyhnethyl)-iV -salicyliden-1,2-diaminoethane). The one-electron oxidized complex [Mn2 0(F)2] + has been electrochemically prepared and crystallized and is the only example of a structurally characterized mono-oxo bridged Mn2(III,IV) complex. 

Treatment of the Schiff base tin(n) species Sn(salen) (salen = N,N -bis(salicylidene)ethylenediamine) with a solution of Cp2TiCl2 in GH2C12 affords the mono-Cp complex CpTiCl(salen) (Scheme 416), accompanied by SnCpCl.996... 

While Schiff bases are generally photochromic in rigid glasses irrespective of how they behave in the solid state, iV-salicylidcncbcnzylamines, A -salicylidcnc-2-phenylethylamines, iV-salicylidene-2-aminomethylpyridines, and /V-salicylidcnc-2-aminoethylpyridines investigated in methylcyclohexane isopentane at 77 K or... 

N. Hoshino, T. Inabe, T. Mitani and Y. Mamyama, Structure and optical properties of a thermochromic Schiff base Thermally induced-intramolecular proton transfer in the N,N bis(salicylidene)-p-phenylenediamine crystals, Bull. Chem. Soc. Jpn. 61, 4207-4214 (1988). 

Two Schiff bases (A,iV -bis(5-bromosalicylidene)-1,2-diamino-ethane and 7-[( 1 -(5-bromo-2-hydroxyphenyl)methylidene)amino]-4-methyl-coumarin), and two appropriate Schiff-Mannich bases (A,JV-bis(5-bromo-3-[(diethylamino)methyl]salicylidene)-1,2-diaminoethane and 7-[( 1 -(5-bromo-3-[(diethylamino)methyl]-2-hydroxyphenyl)methylidene)amino]-4-methylcoumarin) capable of intramolecular hydrogen bonding have been investigated by multi-nuclear NMR methods in both solid and liquid phases. In all of the compounds under investigation tautomeric equilibrium involving an intramolecular hydrogen bond has been found. In the solid state the tautomeric... 

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