A remarkable skeletal rearrangement of a coordinated tetrapyrrole: Chemical consequences of palladium pi-coordination to a bilindione

Pd-4(OEB)(2), in which a [Pd-2](2+) unit is bound in pi -fashion to olefini c sites that are exocyclic, to pyrrole rings of the octaethylbilindione lig and, undergoes an unprecedented sequence of reactions that results, in the rearrangement of the framework of the bilindione ligand and the formation o f trans-Pd(py)(2)I-2. This process of bilindione. rearrangement and oxidati on occurs as a direct consequence of the pi -coordination of the palladium. The reaction results in the migration of a nitrogen atom from a pyrrole ca rbon atom to what was formerly a meso carbon atom to transform a former pyr role 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 ox ygen atom (from water) not necessarily in this particular sequence.