Triflate-Selective Suzuki Cross-Coupling of Chloro- and Bromoaryl Triflates Under Ligand-Free Conditions.

In the absence of strong ancillary ligands such as phosphines or N-heterocyclic carbenes, palladium salts are selective for C-OTf cleavage in the room-temperature Suzuki couplings of chloroaryl triflates in acetonitrile. Similar "ligand-free" conditions in DMSO also promote triflate-selective Suzuki coupling of bromoaryl triflates. This triflate selectivity complements the typical preference for reaction of bromides in prior reports of Suzuki couplings using phosphine ligands. DFT calculations and additional experimental evidence are consistent with triflate-selective oxidative addition taking place at homogeneous, possibly mononuclear, anionic palladium supported by a solvent molecule.