Sepulchrates tris

The platinum(IV), rhodium(III), and iridium(III) sepulchrates, dinitrosarcophaginates, and diaminosarcophaginates have been synthesized in high yields (45-65% for Pt(IV), 40% for Ir(III), and 90-100% for Rh(III)) starting from their tris-ethylenediaminates [94, 156, 157]. The rhodium (III) and iridium(III) complexes were prepared in a similar manner to that for cobalt (III) complexes, except of the elevated temperatures (Rh, 60°C Ir, 90°C) required for the quoted yields. Moreover, if chiral [Rh(en)3] cation was used initially, clathrochelate complexes were obtained in ca 100% chemical and chiral yields, despite the seven centres of chirality [157]. 

Attempts of Sargeson and coworkers [158] to cross-link the chromium(III) tris-ethylenediaminate have not been successful because of rapid dissociation of intermediate imine species. However, Endicott and coworkers [159] have managed to synthesize chromium(III) sepulchrate, not isolating its tris-ethylenediaminate, upon heating of anhydrous chromium sulphate with concentrated aqueous ethylenediamine for several hours followed by the addition of formaldehyde and ammonia with constant heating. The... 

Closely related to the football ligands are the so-called sepulchrate ligands. One can be formed by the condensation of formaldehyde and ammonia onto the nitrogen atoms of tris(ethylenediamine)cobalt(llI). This results in tris(methylene)amino caps on opposite faces of the coordination octahedron. If the synthesis utilizes one of the (A, A)-enantiomers, the chirality of the complex is retained. Furthermore, the complex may be reduced to the corresponding cobalt(II) cation and reoxidized to co-balt(III) without loss of chirality. This is particularly unusual in that, as we shall see in the following chapter, cobalt(ll) complexes are quite labile in contrast to the stability of cobalt(III) complexes. Once again the extra stability of polydentate complexes is demonstrated. 

Cobaltate, tris(l, 2-ethanediamine)-racemization solid state, 466 Cobaltate, tris(oxalato)-racemization solid state, 467 Cobaltates sepulchrates, 22 Cobalt complexes geometric isomerism, 11 hexaammine... 

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