Synthesis and Computational Studies of Palladium(I) Dimers Pd2X2(PtBu2Ph)2 (X = Br, I): Phenyl versus Halide Bridging Modes

The synthesis and characterization of the new palladium(I) dimer Pd₂Br₂(nu-P^tBu₂Ph)₂ (8) is reported herein. The single-crystal X-ray analysis of this compound has shown that the phosphine acts as a bridging ligand between the two palladium centers, using the phosphorus atom as well as the ipso- and ortho-carbon atoms of the phenyl substituents. An analysis of the electronic structure indicates that the bond between the remote palladium center and the bridging ligand is stabilized by two distinct electronic components, one with the C=C bond of the arene, the other an agostic-type interaction with the P-C bond. The steric bulk at the phosphorus center causes distinct changes in the relative contributions of these two components and, hence, distorts the structure. In contrast, the iodide analogue (9) adopts a completely different structure, where the phosphines are terminally coordinated and the halide acts as a bridging ligand.