Bridging Coordination of Vinylarenes to Pd3 - or Pd4 Cluster Sites.

Though the M3 - or M4 face of palladium clusters may serve as the active binding site of substrates, it has been difficult to elucidate their substrate binding modes in solution. Here, it was proved that a soluble Pd3 - or Pd4 sheet cluster accommodates vinylarenes at its bridging coordination site in an unusual mode in palladium chemistry; that is, for the former, the coordination of the arene moiety precedes that of olefin moiety; for the latter, vinylarene coordinates to a distorted Pd4 sheet through oxidative π-addition of its styrene moiety.