Chromium complexes configuration

The configuration of these complexes were established on the basis of IR and H-NMR spectra (62). When triphenylarsine was reacted with sulfoxonium ylide complex, pentacarbonyl triphenylarsonium ylide-chromium complex was obtained (95). 

It has already been stated that chromium complexes of tridentate metallizable azo compounds occupy their position as the single most important class of metal complex dyestuffs because of their high stability. It should be noted, however, that in this context the term stability is not used in the thermodynamic sense but relates to the kinetic inertness of the complexes.25 Octahedral chromium(III) complexes have a tP electronic configuration and the ligand field stabilization energy associated with this is high.26 Ligand replacement reactions involve either a dissociative... 

In 1939, Drew83 proposed structures for 2 1 chromium complexes of o,octahedrally coordinated to the central chromium ion (81). Pfitzner71 independently arrived at the same conclusion and 2 1 chromium complexes having this equatorial or meridional (mer) configuration have been described84 as Drew—Pfitzner types. This configuration permits only an enantiomeric pair of isomers. 

Support for Schetty s postulates has been provided by X-ray crystal structure determinations. Thus the 2 1 chromium complexes (126) and (127) of the two o,o -dihydroxydiarylazo compounds 2,2 -dihydroxyazobenzene and l-(2-hydroxy-4-nitrophenylazo)-2-naphthol, respectively, have been proved89 to have meridional configurations, whilst the 2 1 chromium complex (128) of the o-carboxyarylazopyrazolone l-(4-brornophenyl)-3-methyl-4-(2-methyl-6-carboxyphenylazo)-5-pyrazolone has been proved90 to have a facial configuration. 

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... 

For example, by chromatographic techniques it can be shown that the 1 2 chromium complex 15 exhibits only one isomer (a,a form), the mixed 1 2 chromium complex 16 two (a,a and a,(3 forms), and the symmetric 1 2 chromium complex 17 three isomers (a,a, a,(3 and (3,(3 forms), assuming that these dyes exist only in the mer configuration. 

Staggered configurations have also been observed for the tricarbonyl chromium complexes of phenanthrene 294, 295), 9,10-dihydro-phenanthrene 293, 295), anthracene 202), naphthalene 262), and 1-aminonaphthalene 58). The eclipsed configuration has been observed for the tricarbonyl complexes of anisole (57, 229), toluidine 60, 61), methylbenzoate (59), o-methoxyacetylbenzene, o-hydroxyacetylbenzene 101), 2-methoxy-[l-hydroxy-ethyl]benzene (99), and 2-methyl-[l-hydroxy-l-phenylpropyl]benzene (97). It is apparent that the orientation of the chromium tricarbonyl moiety is in many cases controlled by the substituents on the ring to which it is coordinated, and this has been attributed to mesomeric electron repulsion or withdrawal by the substituents 374). 

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