Trinuclear palladium addition to unsaturated carbocycles

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 PdII centers through a synfacial η3:η1:η3:η1 coordination mode. The tetraanionic COT ligand bearing three PdII moieties undergoes a unique intramolecular 1,5-C–C coupling.