Sepulchrates synthesis

In all cases mentioned, the spectral and X-ray diffraction data on reaction intermediates and by-products have widely been used in considering kinetic and thermodynamic relationships. The identification of intermediates and by-products is still more important in determination of the mechanisms of sarcophaginate and sepulchrate synthesis because in this case kinetic approaches cannot be used. 

A.-M. Sepulchre, G. Lukacs, G. Vass, and S. D. Gero, Synthesis and pulse Fourier transform 13C NMR spectra of branched-chain carbohydrates, Angew. Chem. Int. Ed., 11 (1972) 148. 

Fig. 8 Template synthesis of the cobalt(III) sepulchrate complex, [Coffl(sep)]3+. Step i complex formation and oxidation by air step ii Schiff base condensation step iii nucleophilic attack to the C=N double bond by the deprotonated forms of ammonia...

The corresponding macrobicyclic cobalt(II) [Co(sep)](ZnCl4) H20 complex was prepared by reduction of the [Co(sep)]Cl3 complex with zinc dust in aqueous HCl [95], A similar procedure was used for the synthesis of the dithionate [Co(sep)](S206) salt in the presence of Li2S206 [99], The optically active R- and S-isomers of cobalt sepulchrate were obtained from the optically active parent A-[Co(en)3]Cl3 and A-[Co(en)3]Cl3 complexes [94-95],... 

The template synthesis of the nickel sepulchrate proved to be rather complicated because of macrocyclic and acyclic amines (Scheme 69), competitive formation reactions occurred upon refluxing ethylenediamine, formaldehyde, and ammonia in the presence of Ni + ion. 

As mentioned above, a template synthesis is a very efficient approach to the preparation of sarcophaginates and sepulchrates of certain metals. For all other metal ions, this synthetic pathway is inapplicable or gives the desired products in low yields. For instance, the yields of nickel(II) and chromium(III) sepulchrates resulting from template condensation are only ca 1 and 10%, respectively. This problem can largely be overcome if the synthesis of a variety of metal... 

Methods for the synthesis of sarcophaginates and sepulchrates based on redox and photochemical reactions are discussed in Chapter 5. 

Goedken and Peng s idea to employ the reaction between the amino groups, bound to the metal ion, and formaldehyde for the synthesis of clathrochelates proved to be beneficial. It has served as a basis for later studies of Sargeson and coworkers on the synthesis of sepulchrates and sarcophaginates. 

The fact that the synthesis of sarcophaginates and sepulchrates proceeds via the formation of an imine complex was also confirmed by isolation of the semiclathrochelate [Co(sen)]- + complex (as a by-... 

The mechanism proposed for the formation of the sepulchrates accounts for the fact that, despite seven chiral centres and six nitrogen-metal bonds, the synthesis of [Co(sep)] + cation yields only one isomer. After the formation of the first heminal diamine and second imine centre, the chiral nitrogen centre must be oriented so that the methylene unit of the amine fragment and the proton are apical and equatorial, respectively, before intramolecular cycli-zation. In this case, six-membered ring closure takes place. The same apical orientation of the six-membered chelate cycle must be retained to complete the formation of a capping group. After the completed encapsulation, the methylene unit and the proton cannot... 

Semenia D, Philippe M, Delaumeny J-M, Sepulchre A-M, Gero SD (1983) Synthesis 710... 

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. 

Semiquinone, 3,5-di-/-butyl-chromium complexes, 398 Semiquinones metal complexes, 398 Sepulchrates classification, 920 metal ion complexes, 940 synthesis, 927 Serine... 

J. Cleophax, J. Hildesheim, A.-M. Sepulchre, and S.D. Gero, Synthesis of epimino tetra-hydrofurans. Bull Soc. Chim. Fr. (1969) 153-156. 

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