Y-Shaped Tris-N-Heterocyclic-Carbene Ligand for the Preparation of Multifunctional Catalysts of Iridium, Rhodium, and Palladium

A series of homo- and hetero-dimetallic complexes of
Ir, Rh, and Pd have been obtained using our previously reported Y-shaped
tris-NHC ligand. The new complexes can be obtained through the isolation
of the corresponding monometallic intermediates (in which the ligand
always coordinates in a chelating form) or by a one-pot stepwise synthetic
protocol that avoids the isolation of the intermediate. The catalytic
properties of the Ir–Pd complexes have been explored in two
tandem processes: dehalogenation/transfer hydrogenation of haloacetophenones
and Suzuki-coupling/transfer hydrogenation of p-bromoacetophenone.
These two complexes have been also tested in two model reactions typically
catalyzed by iridium (cyclization of 2-aminophenyl ethyl alcohol to
yield indole) and palladium (acylation of bromobenzene with n-hexanal).