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.