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.