meta- and para-Phenylenediamine-Fused Porphyrin Dimers: Synthesis and Magnetic Interactions of Their Dication Diradicals.

meta- and para-Phenylenediamine-fused nickel(II) porphyrin dimers were synthesized by S Ar reaction of meso,β,β-trichloro nickel(II) porphyrin with meta- and para-phenylenediamines and subsequent Pd-catalyzed intramolecular C-H arylation. Their tetrachlorinated dication diradicals are very stable, allowing SQUID magnetometry and revealing clear open-shell characters for both meta and para isomers with ferro- and anti-ferromagnetic interactions, respectively. The nitrogen analogue of Thiele's hydrocarbon usually displays predominant closed-shell nature but its hidden diradical characters increase either in a twisted conformation or upon insertion of an additional phenylene spacer. The observed distinct diradical nature of the para-congener indicates that diradical properties can be enhanced also by efficient spin delocalization.