Catenation of heterocyclic non-Kekule biradicals to tetraradical prototypes of conductive or magnetic polymers

Methods are described for the synthesis of bis-diazene precursors of catenated tetraradicals. Photodeazetation in a low-temperature matrix of the N-tosylpyrrole member of the series (13) gives mainly the monodeazetated biradical 34, which is characterized by its ESR spectrum as a triplet species. Determination of the absolute number of spins present and analysis of the kinetics of the photolysis show that the tetraradical 12 is present to the extent of only 0.2-0.5% of the concentration of the biradical. The spectrum of the tetraradical 12 therefore cannot be observed under these conditions, and its spin remains unknown. Photodeazetation of the bis-diazene precursor (35) in the thiophene series gives successively the green monodeazetated biradical 36 and the (also green) bis-deazetated tetraradical 11. The reactions of compound 11 with alkenes in thawed matrices and its lack of an ESR spectrum characterize the species as a singlet. The tetraradical 11 is a prototype of a nonclassical polymeric conductor. Because of the presence of ''half-filled'' NBMOs, the frontier electrons of such molecules may be exceptionally conductive.