A Detailed Study of Acetate-Assisted C–H Activation at Palladium(IV) Centers

This
report describes a detailed investigation of acetate-assisted C–H
activation at PdIV centers supported by the tris­(2-pyridyl)­methane
(Py3CH) ligand. Mechanistic information about this transformation
has been obtained through the following: (i) extensive one- and two-dimensional
NMR analysis, (ii) reactivity studies of a series of substituted analogues,
and (iii) isotope effect studies. These experiments all suggest that
C–H activation at [(Py3CH)­PdIV(biphenyl)­Cl2]+ occurs via a multistep process involving chloride-to-acetate
ligand exchange followed by conformational and configurational isomerization
and then C–H cleavage. The data also suggest that C–H
cleavage proceeds via an acetate-assisted mechanism with the carboxylate
likely serving as an intramolecular base. The viability of acetate-assisted
C–H activation at high valent palladium has important implications
for the design and optimization of catalytic processes involving this
transformation as a key step.