Green synthesis of substituted olefins (Heck Cross-Coupling Reaction) with palladium(II) catalysts bearing heterodonor P/N ligands

Abstract

To develop new hemilabile ligand systems for the green synthesis of substituted olefins via Heck cross-coupling reactions in supercritical CO2, we designed and synthesized three palladium(II) complexes bearing heterodonor phosphine-imine ligands which were effectively used in organic solvents in terms of various Pd-catalyzed cross coupling reactions. These newly prepared palladium(II) complexes and previously reported analogs by us were modified with perfluorooctyl (-C8F17) groups to provide their solubilization in supercritical CO2 to be applied as homogenous catalyst. Both catalytic efficiency and selectivity were benchmarked in the Heck cross-coupling reactions, this representing the first example of the use of hemilabile phosphine-imines as ligands in supercritical CO2 solvent. This ligand system leads to lower reaction times, good conversions and selectivities than the previously reported well-known monoor bisphosphine palladium precatalysts. Moreover, the phosphine-imine based palladium(II) precatalysts show tolerance of a wide variety of substrates on both olefin and aryl halides.