Abstract

The literature survey about the title subject since 1985 is presented. The new heterocycles are classified by the tetracyanoethylene (TCNE) reaction type. Accordingly, four classes of TCNE-derivative heterocycles can be identified: (i) reaction products obtained by nucleophilic attack on tetracyanocyclopropanes, which in turn are formed from the reaction of TCNE with aliphatic monobromoderivatives; (ii) products resulting from the thermal decomposition of unstable charge-transfer compounds of TCNE and an electron-donor; (iii) Diels-Alder cycloadducts between TCNE and a diene; (iv) products derived from previously unknown reaction of TCNE. The most interesting new heterocyclic compounds belong to the last (iv) class of TCNE-derivatives, where the 2-(5-amino-3,4-dicyano-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide (L), synthesized for the first time by the author after the reductive autocondensation of TCNE promoted by Lewis acids, occurs too. Further, we report on the properties of L both as metal-chelating ligand and material for sensor applications. L undergoes an intramolecular cyclization to the 1,2,6,7-tetracyano-3,5-diimino-3,5-dihydropyrrolizinide (L) on coordination to transition metal cations. A number of metal-complexes of L, either mono- (ML) or bispyrrolizinates, M(L)2, have been isolated and structurally characterized. The most interesting property of these species is that they are metal-phthalocyanine-like dyes and thus they may be useful for the interpretation of the electronic structure of porphyrinic systems. The protonation of L furnishes the neutral 5-amino-3-imino-1,2,6,7- tetracyano-3H-pyrrolizine (HL). Like other similar conjugated heteropolycyclic molecules and their conjugated anions and complexes, L and all its derivatives show suitable properties for application in the construction of optochemical sensors, potentially useful for detecting species of environmental interest.

Keywords: tetracyanoethylene, tcne-derivative heterocycles, metal-complexes, bispyrrolizinates, tetracyano-3h-pyrrolizine