Influence of Electronically and Sterically Tunable Cinnamate Ligands on the Spectroscopic Properties and Reactivity of Bis(triphenylphosphine)platinum(0) Olefin Complexes

A total of 48 new bis­(triphenylphosphine)­(cinnamic acid ester)­platinum(0) complexes were synthesized to examine electronic and steric influences on their behavior as inhibited precatalysts and to correlate this with 1H, 13C, 19F, 31P and 195Pt NMR spectroscopic, IR spectroscopic, and X-ray structural properties (9 X-ray structures included). The substituent at the 4-position of the phenyl group proved to be a valuable moiety in controlling the electronic properties of the olefin ligand and, therefore, the metal–ligand bond strength. Reactivity and NMR spectroscopic data correlate with the Hammett parameters of this substituent: in particular, the coupling constants 2JPP and 1JPPt. The reactivity of the complexes was determined via NMR titration with triphenylphosphine (1H NMR; triggering ligand substitution) and reaction with diphenylsilane (1H and 29Si NMR; triggering oxidative addition). The determined equilibria correlate with the electron density of the olefin. As one quintessence the reactivity can be predicted indirectly from the NMR 2JPP coupling constants of the complexes, as was also found for the related Pd complexes.