Chromium complexes isomerization

Naphthol, l-(2-carboxyphenylazo)-chromium complex geometrical isomerism, 6, 68 2-Naphthol, l-(2-hydroxy-4-nitrophenylazo)-chromium complexes geometrical isomerism, 6, 69 2-Naphthol, l-(2-hydroxyphenylazo)-chromium complex... 

It should be noted that 175 is the chromium complex of 154, the intermediate postulated in the thermal isomerization of hexamethyl[6]radialene (150). 

A further 20 years elapsed before further information became available when Schetty86 published the first of a series87 of papers on this subject in which he described the chromatographic separation of the 2 1 chromium complex of the o-carboxy-o -hydroxydiarylazo compound l-(2-carboxy-phenylazo)-2-naphthol into four components. These had die same me empirical formula but different electronic spectra and solubility properties and, possibly most importantly from the point of view of the dyestuff chemist, each isomerized readily in solution to give an equilibrium mixture of the four components. In marked contrast, only one component was detected when the o,o -dihydroxydiarylazo compound l-(2-hydroxyphenylazo)-2-naphthol was converted into its 2 1 chromium complex. 

The rules governing this type of isomerism appeared, therefore, to be fairly clear but certain glaring exceptions soon became apparent. Thus, Idelson and Karady91 converted the 1 1 chromium complex (129) of l-phenyl-3-methyl-4-(2-hydroxy-4-sulfonaphth-l-ylazo)-5-pyrazolone into the sulfopiperidide and treated the product with pentane-2,4-dione. Chromatography of the reaction... 

A similar argument can be applied to the results of later work by Idelson et al.i9 In this they prepared the chromium complex (133) by interaction of the 1 1 chromium complex of 1-phenyl-3-methyl-4-(2-hydroxy-4-cyanonaphth-l-ylazo)-5-pyrazolone and diethylenetriamine and by reaction of the azo compound with [Cr(CO)3dien]. Identical products were obtained and, since the diethylenetriamine occupies9 a facial position in [Cr(CO)3dien], it was concluded that the complex (133) had a facial configuration. Similarly, the reported77 separation of isomeric 2 1 chromium complexes of 2-amino-6-(2-hydroxy-6-nitro-4-sulfonaphth-l-ylazo)-5-naphthol-7-sulfonic acid is... 

Copper and nickel Chromium and cobalt N -Np Na-Np Meridional/facial coordination Azo/hydrazone tautomerism Non-planarity due to azo/hydrazone tautomerism Formation of two copper and two nickel complexes by unsymmetrical o.o -dihydroxyazobenzenes78 Detection of isomeric 2 1 chromium complexes 79 proton magnetic resonance80 Isolation of isomeric 2 1 chromium and cobalt complexes 86 87 limited X-ray crystallographic89 90 Proton magnetic resonance80 Detection of five isomeric 2 1 chromium complexes of symmetrical o.o -dihydroxydiarylazo compounds... 

Like the corresponding tridentate azo compounds, tridentate azomethines form 2 1 chromium complexes which, in some cases, exist in various isomeric forms. Since coordination is restricted to the nitrogen atom of the azomethine linkage, thus eliminating the possibility of Na—Np isomerism which exists in the analogous azo compounds, this has led to their being used as models in studies of the latter. This is discussed in detail in Section 58.2.3.3(i)(b). 

Castro and Kray have reduced the isomeric butenyl chlorides, using chromous sulfate (5). Again, allylic radicals were proposed as intermediates in the reaction. However, unlike the tin hydride reductions, 1-butene was obtained almost exclusively from each of the isomeric chlorides. The process has been described as occurring within a chromium complex. The preponderant formation of 1-butene from butenyl metal complexes has also been noted by others (12, 23, 46). 

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