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).