Palladium Complexes of the New Porphyrin Isomers ( Z )‐ and ( E )‐Isoporphycene—Pd II ‐Induced Cyclization of Tetrapyrrolealdehydes

Template-controlled syntheses open the way to stable metal complexes of the previously unknown, energy-rich porphyrin structural isomer isoporphycene. The rapid photochemical equilibrium between (Z)- and (E)- octaethylisoporphycene Pd complexes 1 and 2 confirms the prediction that (Z)- and (E)-isoporphycene have similar energies. The small Pd–H distance in 2, a C-C-C bond angle of almost 150° in 1, and parallels in 1H NMR spectra to the all-cis- and the mono-trans-cyclononatetraenyl anion make 1 and 2 very interesting objects of study.