Influence of Electronically and Sterically Tunable Cinnamate Ligands on the Spectroscopic, Kinetic, and Thermodynamic Properties of Bis(triphenylphosphine)palladium(0) Olefin Complexes

A detailed study of the influence of electronic and steric
characteristics
of cinnamic acid esters on the spectroscopic, kinetic, and thermodynamic
properties of bis­(triphenylphosphine)­palladium(0) cinnamic acid ester
complexes is presented (51 different new complexes included). These
complexes show a dynamic behavior on the NMR spectroscopic time scale.
Therefore, the rotational barriers of the olefin about the metal–olefin
bond as well as the dissociation entropy and enthalpy of the olefin
and the dissociation mechanism could be determined. These findings
are interpreted together with the NMR spectroscopic, IR spectroscopic,
and X-ray structural data (7 new structures included) concerning the
influence of the different olefin ligands on the complex properties
by means of Hammett plots. DFT calculations were performed to support
the mechanistic conclusions.