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.