Oxidative Pyrrole Exchange and meso Pyrrylation – Unexpected Reactions of Open‐Chain Tetrapyrrolic 2,2′‐Bidipyrrins

A new hydrogen terminated 2,2′‐bidipyrrin ligand was prepared from a bipyrrole dialdehyde and 3,4‐diethylpyrrole by a POCl₃ induced condensation and isolated as the nickel(II) chelate. Unexpectedly a side reaction occured when base‐deficient and aerobic conditions were chosen in the metalation step. This side reaction led to a novel pentapyrrolic nickel(II) complex with one externally bound pyrrole ring. Further studies showed that the reactions of 2,2′‐bidipyrrins with 3,4‐diethyl‐ or 2,3,4‐trimethylpyrrole and an oxidant resulted in a stepwise exchange of the terminal pyrrole moieties and, in the former case, the introduction of one additional pyrrole ring into one of the two meso positions of the open‐chain tetrapyrrole.