Benzylic Complexes of Palladium(II): Bonding Modes and Pentacoordination for Steric Relief

A large variety of α-(pentafluorophenylmethyl)­benzylic palladium complexes with different ligands have been synthesized and characterized. Multinuclear NMR spectroscopic data allow to determine the σ- or η3-benzylic nature of the complexes in solution. The adoption of either coordination mode is a function of the number of ligands coordinated to palladium, and remarkably, the presence of bulky phosphines favors the adoption of a bidentate η3-benzylic mode and pentacoordinated palladium complexes. Experimental data and DFT calculations indicate that this five-coordination could alleviate the steric hindrance of two bulky cis phosphines. The benzylic complexes show a rich fluxional behavior that involves both ligand exchange and σ- to η3-benzylic interconversion.