Thiophene and Selenophene Binding at a Pd3 Cluster Site.

We report the triply bridging coordination of thiophene and selenophene to a trinuclear metal cluster site. The triply bridging coordination of selenophene at a Pd3 site forms a unique spiro-type Pd5 cluster. Furthermore, either thiophene or selenophene is accommodated stably at a Pd3 site supported by a backside µ3 -cyclooctatetraene ligand through the face-capping µ3 -coordination. The Pd3 site supported by the cyclooctatetraene ligand showed higher binding affinity of benzene over thiophene, although a Pd2 site strongly favors thiophene over benzene.