Trinuclear palladium addition to unsaturated carbocycles

Abstract

The trinuclear palladium addition to monocyclic unsaturated hydrocarbons was revealed. The trinuclear adduct of [2.2]paracyclophane, cycloheptatriene (CHT), or cyclooctatetraene (COT) was obtained by treatment of the corresponding tripalladium sandwich complexes with 3 equiv. of 1,10-phenanthroline. In the trinuclear adduct of [2.2]paracyclophane or CHT, a Pd₂ unit and a Pd₁ unit synfacially coordinate through a (μ–η³-allyl):(η³-allyl) manner. A trinuclear adduct of COT exhibited an unusual bonding structure in which a formally tetraanionic COT coordinates to three Pd^II centers through a synfacial η³:η¹:η³:η¹ coordination mode. The tetraanionic COT ligand bearing three Pd^II moieties undergoes a unique intramolecular 1,5-C–C coupling.