Experiment and Theory of Bimetallic Pd-Catalyzed α‑Arylation and Annulation for Naphthalene Synthesis

We
report the synthesis of bimetallic Pd­(I) and Pd­(II) complexes
with bidentate 2-phosphinoimidazole ligands and their catalytic activity
to generate substituted naphthalenes. This process involves the coupling
of an aryl iodide and 2 equiv of a ketone via sequential ketone α-arylation
and then annulation to generate disubstituted and tetrasubstituted
naphthalenes in a regioselective manner. Excellent substrate scope
for both aryl iodide and ketone partners is demonstrated, including
that for heteroaryl iodides. Bimetallic Pd complexes are much more
reactive than monometallic Pd catalysts in this transformation. Density
functional theory calculations, isotope effect experiments, and substrate
competition experiments were used to examine bimetallic mechanisms,
reactivity, and selectivity.