4631370474

306 J. EILMES, M. PTASZEK

ABSTRACT

The title dibenzotetraaza[14]annulenes (Fig. 1) belong to the cłass of the synthetic tetraaza macrocyclic ligands of bioinorganic relevance. Their similari-ty to porphyrins makes them attractive as models of important biological systems like for example hemoproteins (hemoglobin, myoglobin), cytochromes and metalloenzymes (e.g. oxygenases, peroxidases, catalase) [2, 4].

Dibenzotetraaza[14]annulene and porphyrin ligand both have four co-planar nitrogen donor atoms and substantial bond unsaturation and delocaliza-tion in the macrocyclic framework. However, the dibenzotetraaza[14]annulenes are Huckel anti-aromatic (4n), whereas the porphyrins are fully delocalized aro-matic (4n + 2). There is also remarkable difference in the conformation of the macrocyclic ligand which is fiat in porphyrins and taa system (R_t = R₃ = H) and saddle-shaped in the case of other dibenzotetraaza[14]annulenes (R_x = = R₃ H). The conformation of the ligands greatly influences the metal coor-dination geometries in their metal complexes. Structure of the dibenzotetra-aza[14]annulenes is discussed in details in Part II.

The purpose of this article is to provide the readers with the preparative methods of the synthesis of various dibenzotetraaza[14]annulenes. Reactivity of the macrocyclic framework is also reviewed, as a method of further modifica-tion of the ligand structure.

Ali synthetic methods are divided into two distinct categories, known as non-template and metal-ion template procedures. In the first case, the 2 + 2 condensation of the substrates takes place leading in one step to dibenzotetra-aza[14]annulene ligand. The non-template approach is especially well suited for the synthesis of the H₂taa ligands (R_t = R₃ = H) and is exemplified by the reaction of n-phenylenediamine with propynal [8, 9], malondialdehyd [11, 12], acroleine and its derivatives [13-15], as well as with vinamidinium salts [16] (Schemes 2-8).

In the template procedures, similar condensation reactions are catalytically improved by metal ions, usually Ni^{2 +} (in some instances also Co~⁺ or Cu^{2 h}), leading to corresponding metal complexes of the dibenzotetraaza[14]annulencs (R_t = R₃ # H). Demetallation procedures have to be employed in this case, in order to isolate free ligands [7, 21, 25]. The most often cited template reactions are described in the papers [17-21] and outlined in Schemes 9 13.

The y,y' positions of the dibenzotetraaza[14]annulenc ring appeared to be the reactive nucleophilic centres. The reactions with diazonium salts [36, 37], halogenation [38], alkylation [56], acylation by mcans of mono- and dicar-boxylic acids chlorides [39-44, 47] give rise to corresponding mono- and disub-stituted produets. A wide rangę of 7,16-substituted derivativcs of the diben-zotetraaza[14]annulene complexes have been synthesized by the reaction with