A Remarkable Skeletal Rearrangement of a Coordinated Tetrapyrrole: Chemical Consequences of Palladium π-Coordination to a Bilindione

Pd4(OEB)2, in which a [Pd2]2+ unit is bound in π-fashion to olefinic sites that are exocyclic to
pyrrole rings of the octaethylbilindione ligand, undergoes an unprecedented sequence of reactions that results
in the rearrangement of the framework of the bilindione ligand and the formation of trans-Pd(py)2I2. This
process of bilindione rearrangement and oxidation occurs as a direct consequence of the π-coordination of the
palladium. The reaction results in the migration of a nitrogen atom from a pyrrole carbon atom to what was
formerly a meso carbon atom to transform a former pyrrole ring into a six-membered ring. This process also
involves cleavage of the Pd−Pd and Pd−C bonds, oxidation of palladium, and introduction of an oxygen
atom (from water) not necessarily in this particular sequence.