Synthesis and Structure of Multinuclear Pd(II) Complexes Bridged by Phosphide or Azide Ligands.

The synthesis and structure of phosphide- and azide-bridged multinuclear Pd(II) complexes bearing phosphine ligands [PdX(μ-X')(PR)] (X = Cl and N; X' = PR and N; = 2 and 4) are reported. The oxidative addition of R PCl to Pd(PMe) furnished the phosphide-bridged dinuclear Pd(II) complexes [PdCl(μ-PR )(PMe)] [R' = Pr () and Cy ()]. However, the oxidative addition of (-tolyl)PCl to Pd(PMe) produced a nonbridged mononuclear Pd(II) complex with the bis(-tolyl)phosphinic ligand, -[Pd(PMe){P(O)(-tolyl)}] (), via oxidation of the phosphinyl ligand. The reaction of the chloride-bridged dinuclear Pd(II) complexes [PdCl(μ-Cl)(PR)] [PR = PEt () and PPhMe ()] with NaN afforded the azide-bridged dinuclear and tetranuclear Pd(II) complexes [Pd(N)(μ-N)(PEt)] () and [Pd(N)(μ-N)(PPhMe)] (). Comparisons of the X-ray structures of and show that the square-planar molecular geometry of the Pd(II) centers of are more distorted than those of . Density functional theory calculations suggest that the tetranuclear eight-membered ring structure like is more stable than the dinuclear four-membered ring structure like in the gas phase in both PEt and PPhMe systems. However, because the relative energy difference between the four-membered and eight-membered ring structures is small in the PEt system with smaller steric hindrance compared with PPhMe, it is assumed that this difference is compensated by the crystal packing energy, and the dinuclear four-membered ring complex is actually obtained.