Metal complexes with 1-hydroxyanthraquinone and its derivatives: Electronic absorption spectra and ligand structures

Reactions of metal salts with 1-hydroxyanthraquinone and its derivatives gave tautomeric 9,10-and 1,10-quinoid complexes and compounds containing no C=0 → M coordination bond. Each form is characterized by a single π₁,π*-band. The absorption bands were assigned by using correlations with the σ^A-constants of the hydroxy and oxido groups for tautomeric anthraquinones. Complexes with nonionized ligands have particularly the 9,10-anthraquinoid structures; complexes with ionized ligands can form both 9,10-and 1,10-quinoid structures.     

Quantum-chemical and correlation study on tautomerism and ionization of Quinalizarin

Quinalizarin and anions derived therefrom exist as equilibrium mixtures of different tautomers and conformers, whose structure depends on the conditions. Quinalizarin was shown to have 9,10-, 1,10-, 1,4-, 1,5-, 1,7-, and 2,9-quinoid structures, but not 1,2-quinoid structure; and its anions in ethanol media were identified as 9,10-, 1,10-, 2,9-, and 1,5-quinoid tautomers. Interactions with solvents and ionization could give rise to displacement of tautomeric and conformational equilibria, leading to considerable change in the number and position of π _l ,π* bands in the electronic absorption spectra, which are responsible for the color.     

Quantum-chemical and correlation study of the tautomerism and ionization of 1,2,3-Trihydroxy-9,10-anthraquinone

1,2,3-Trihydroxy-9,10-anthraquinone (anthragallol) exists as an equilibrium mixture of the 9,10-, 2,9-, 1,2-, and 2,3-quinoid tautomers. Its anion was detected in the 9,10-, 1,10-, 2,9-, and 2,3-quinoid forms, and its metal complexes, the 9,10-and 2,9-quinoid forms. Ionization and complexation of anthragallol can shift the tautomeric equilibrium.     

Anthraquinones tautomerism: VII. Hydroxy-substituted anthraquinones

Tautomerism of β-mono-, β,β′-dihydroxyanthraquinones, and their anions was studied for the first time by quantum-chemical and correlation methods. 2-Hydroxyanthraquinone exists exclusively in 9,10-quinoid form, and its ionization involves a tautomeric transformation into 10-oxido-2,9-anthraquinone. β,β′-Dihydroxyanthraquinones can exist as the corresponding 9,10-, 2,9-, 2,6-, and 2,3-quinoid tautomers, and the most characteristic forms of their anions are 2,9-quinoid structures. The considerable difference in the known spectra of the same compound is due to the shifts of the tautomeric equilibria.     

Tautomerism of anthraquinones: VIII. Tautomerism and conformations of 1,4-diamino-9,10-anthraquinone

The compound widely known as 1,4-diamino-9,10-anthraquinone is in fact an equilibrium mixture of 4,9-diamino-1,10-anthraquinone and tautomeric imino forms, 10-amino-9-hydroxy-1,4-anthraquinone 1-imine and its conformer, and 4-amino-1-hydroxy-9,10-anthraquinone 9-imine or 4,9-dihydroxy-1,10-anthraquinone diimine. Amino-imino tautomerism and rotational isomerism are responsible for fine structure of the π_l,π*-absorption of the title compound.     

Competing tautomeric transformations and the structure of 1-(alkyl,aryl)amino-4-hydroxyanthraquinones

Keto-enol and amine-imine tautomerism and equilibria with trans-conformers are characteristic of 1-(alkyl,aryl)amino-4-hydroxy-9,10-anthraquinones. Amino forms possess 1,10- and 1,4-, but not 9,10-quinoid structure. Various tautomeric and conformeric transformations are in competition. The outcome of this competition may be studied by the correlation analysis of electron absorption spectra but it would be possible to understand the causes of changes in the direction of the competing transformation only in the case when each action on the substance would be accompanied with establishing the corresponding alterations in its tautomeric composition.     

Role of tautomerism and rotational isomerism in the interaction of α-hydroxyanthraquinones with boric acid

The products of reaction of α-hydroxyanthraquinones with boric acid are mixtures of 9,10-, 1,10 -, 1,4- and 1,5-quinoid tautomeric complexes of boric acid and borate esters differing by the coordination bonds with carbonyl groups existing in the dynamic equilibrium. The deepening of the reagents color in the presence of boron does not a result only of the complexation, but in the accompanying shift of the tautomeric equilibria.     

Tautomerism of anthraquinones: X. Quinizarin boron complex

Products of reactions of hydroxyanthraquinones with boric acid exist as equilibrium mixtures of tautomeric boron complexes and boric acid esters in which one or two boron atoms are not coordinated to carbonyl groups. Tautomerism is responsible for the appearance of several π_l,π bands in the electronic absorption spectra and considerable differences in the data obtained by different authors. Boron-containing quinizarin derivatives have mostly 1,10-quinoid structures. The use of quinizarin as an analytical reagent for the determination of boron is based on replacement of tautomeric equilibria due to complex formation rather than on coordination-induced red shift of the absorption maximum.     

Tautomerism of anthraquinones: IV. 1-Hydroxy-9,10-anthraquinone and its substituted derivatives

1-Hydroxyanthraquinone and its substituted derivatives exist as equilibrium mixtures of four tautomers and rotational isomers. Their anions have 9,10-and 1,10-quinoid structures. Each tautomer or conformer is characterized by a single π₁,π* band in the electronic absorption spectrum.     

Tautomerism of Anthraquinones: I. Purpurin and Anions Derived Therefrom

A procedure was proposed for quantitative analysis of tautomeric equilibria of organic compounds. Purpurin was found to exist mainly as 9,10-, 1,4-, and 1,10-anthraquinoid tautomers, its monoanion, as 1,10-anthraquinoid tautomer, the dianion, as 1,10- and 2,9-anthraquinoid tautomers, and the trianion, as 1,10-, 1,4-, and 2,9-anthraquinoid tautomers. Tautomeric transformations occur both in the ground and in the excited states, and the corresponding changes of quantum-chemical parameters in these states are essentially different. The excited states are more sensitive to tautomeric transformations than the ground states.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 1, 2005, pp. 43–50.Original Russian Text Copyright © 2005 by Fain, Zaitsev, Ryabov.     

Metal Complexes with Alizarin Complexone AC: Electronic Absorption Spectra and Ligand Structure

The character of the electronic absorption spectra of metal complexes with alizarin complexone AC is determined by the ionization degree of the ligand and the ratio between its excited states with different contributions of tautomeric 9,10-, 1,10-, 2,9-, and 1,2-anthraquinoid resonance structures. It was found by the spectrophotometric, quantum-chemical, and correlation methods that the ligand in metal complexes can exist in three forms, namely, neutral and two ionized forms (containing one or two deprotonated hydroxy groups). For each of the latter two forms, four excited states with the dominating contribution of the 9,10-, 1,10-, 2,9-, or 1,2-anthraquinoid resonance structures are possible. The formation of red monometallic complexes involves the peri- or ortho-hydroxycarbonyl group in anthraquinoid tautomers (mostly, 1,2- and 2,9-structures). The color of bimetallic complexes is determined by four anthraquinoid structures of the ligand (from red 9,10- to blue 1,10-anthraquinones). Fluorine-containing complexes exist only as 1,2- and 1,10-anthraquinoid structures, which are responsible for their blue color. The known metal complexes with Alizarin Complexone AS were classified by their structures.     

Single crystal x-ray diffraction study of dioxane,pyrazine, and pyridine complexes of 3-(1-amino-2,2,2-trifluoroethylidene)-2-imino-1,1,4,5,6,7-hexafluoroindan

Single crystals of complexes of 3-(1-amino-2,2,2-trifluoroethylidene)-2-imino-1,1,4,5,6,7-hexafluoroindan (1) with 1,4-dioxane, pyrazine, and pyridine have been synthesized. Their structure was investigated by X-ray analysis. In crystals of the dioxane complex, compound 1 is present together with its tautomer — 2-amino-3-(1-imino-2,2,2-trifluoroethyl)-1,1,4,5,6,7-hexafluoroindene (1a), and these compounds are in an equilibrium ratio of ～60:40. Gas-phase quantum chemical calculations have been performed to examine the possibility of a tautomeric equilibrium of enaminoimine 1 in the corresponding complexes.     

Tautomerism of anthraquinones: V. 1,5-Dihydroxy-9,10-anthraquinone and its substituted derivatives

1,5-Dihydroxyanthraquinone and its substituted derivatives are capable of existence in the states structurally described as 9,10-, 1,10-, and 1,5-quinoid tautomerism, and as rotational isomerism involving a cleavage of intramolecular hydrogen bond. 1,5-Quinoid tautomers are characteristic only of substituted derivatives, and also appear in some metal complexes. The considerable color changes on introducing into the 1,5-dihydroxy-anthraquinone methyl, methoxy, and sulfo groups are caused by the shift in tautomeric and conformer equilibria.     

Tautomerism of metal complexes with 1,8-dihydroxy-3-R1-6-R2-9,10-anthraquinones

The structures of metal complexes with 1,8-dihydroxyanthraquinones studied by spectrophotometric, quantum-chemical, and correlation methods were found to be determined by tautomeric 9,10–1,10-anthraquinoid structures of the ligands and by the degree of the ligand ionization. Complex formation is accompanied by the shifts in tautomeric equilibria influencing both excited and ground states of the ligands. The 1,10-anthraquinoid forms of complexes are the most characteristic. The known complexes are classified in accordance with the ligand structures.     

Tautomerism and ionization of carminic acid

Carminic acid exists as an equilibrium mixture of 9,10-, 1,4-, 1,10-, 2,9-, and 1,7-anthraquinoid tautomers. Its anions have 9,10-, 1,4-, 1,10-, and 2,9-anthraquinoid structures. No conformational equilibria were detected for carminic acid anions. Variation of the solvent and pH and ionization are accompanied by displacements of tautomeric equilibria. Shifts of the long-wave absorption maxima due to tautomeric transformations are determined mainly by change in the energy of the ground rather than excited states of molecules.     

Complexes of some rare earth metals with 1-amino-4-hydroxyanthraquinone

La, Ce(III), Pr, Nd and Sm(III) form very stable reddishviolet 1:1 complexes with 1-amino-4-hydroxyanthraquinone in methanol. The stability constants are very similar.     

Metal Complexes with 1,5- and 1,8-Dihydroxy-9,10-Anthraquinones: Electronic Absorption Spectra and Structure of Ligands

Metal complexes with 1,5-dihydroxy-9,10-anthraquinone are studied by the spectrophotometric, quantum-chemical, and correlation methods. It was established that the ligand in these complexes can occur in seven excited states that differ not only in the ionization degree but also in the prevailing contribution of the tautomeric 9,10-, 1,10-, and 1,5-anthraquinoid structures. In all known complexes with 1,8-dihydroxy-9,10-anthraquinone and singly ionized ligand, this ligand has the 1,10-anthraquinoid structure; in complexes with the doubly ionized ligand, the latter ligand most often has the 9,10-anthraquinoid structure. The known complexes are classified according to the ligand structures.     

Structure and Reactivity of the 1,10-Phenanthroline Complex with Nitrenium Cation

According to the X-ray diffraction data, the cationic fragment in 1-amino-1,10-phenanthrolinium mesitylenesulfonate is a unidentate n-complex whose asymmetric structure is retained in solution. Quantum-chemical calculations by the AM1 method and ab initio (6-31G, 6-31G*, MP2/6-31G) give geometric parameters of the cation, which are similar to those determined experimentally. No dynamic processes involving intra- or intermolecular transfer of the NH2 group was observed up to 100°C by NMR spectroscopy. 1-Amino-1,10-phenanthrolinium cation does not react with 4-methylpyridine and 4-methyl-1,10-phenan-throline with transfer of the amino group, and it fails to react with mesitylene and anthracene at elevated temperature.     

Reactions of 9-chloro-1,10-anthraquinone 1-dichlorophosphorylimine with N- and C-nucleophiles

9-Chloro-1,10-anthraquinone 1-dichlorophosphorylimine formed in the reaction of 1-amino-9,10-anthraquinone with PCl₅ followed by dehydrochlorination reacts with primary amines with substitution of chlorine atoms. In the case of aliphatic amines, the reaction occurs further concurrently in two directions: the addition of the amine molecule with the formation of 9,9-di(alkylamino) derivatives of the anthrone and the substitution of hydrogen atom at position 4 with the formation of 4,9-di(alkylamino) derivatives of 1,10-anthraquinone 1-imine. In the case of aromatic amines, 1-amino-9,10-anthraquinone 9-arylimines are the end products. Reactions with the anions of CH-acids containing an alkoxycarbonyl or cyano group occur with substitution in position 9 followed by intramolecular cyclization with the formation of 2-alkoxy- or 2-amino-7H-dibenzo[f,ij]isoquinolin-7-one derivatives, respectively. For preliminary communication, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1179–1184, June, 1998.     

A Quantum-Chemical Study of Prototropic Tautomerism in 1-Hydroxy-9,10-anthraquinones

The effect of substituents R on the tautomerism and electronic absorption spectra of 1-hydroxy-x-R-9,10-anthraquinones and 9-hydroxy-x-R-1,10-anthraquinones was studied by quantum-chemical and correlation methods. The former compounds (x 2) are more sensitive to substituent effects than the latter compounds. Examination of the fine structure of long-wave absorption showed that the experimental spectra of 1-hydroxy-x-R-9,10-anthraquinones contain no bands assignable to ana-quinoid forms.