The 'inverse electron-demand' Diels-Alder reaction in polymer synthesis. Part 4.¹ the preparation and crystal structures of some bis(1,2,4,5-tetrazines)

Reaction of 3,6-bis(3,5-dimethylpyrazolyl)-1,2,4,5-tetrazine with mono- and di-amines gives rise to nucleophilic substitution of one or both of the pyrazolyl substituents, and reaction with diamines under appropriate conditions can lead to bis(3-amino-1,2,4,5-tetrazines), e.g. 12a, 12b and 13. The crystal structures of two of these (12a and 13) show electronic interaction between the tetrazine rings and the amino groups, but none between the tetrazine and pyrazole rings. In 12a there is an extensive network of N-H ⋯ N hydrogen bonds.