Shapeshifting Ligands Mask Lewis Acidity of Dicationic Palladium(II)

Abstract

Supporting ligands limit the degree of electrophilic activation for any substrate because they also reduce the Lewis acidity of the transition metal ion. Here, we temporarily mask the Lewis acidity of dicationic Pd(II) by using “shapeshifting” bidentate pyrimidine/olefin ligands L1 and L2. These ligands delocalize/relocalize charge via reversible C–N bond formation. So, although ligated dicationic Pd compounds [1]²⁺ and [2]²⁺ appear charge separated (distributed across Pd and ligand), they react comparably to a solvated Pd(II) dication. Despite reacting like strong Lewis acids, the complexes are tolerant of polar functional groups (Lewis bases that often inhibit electrophilic catalysis). We propose that this property originates from the installation of a more nucleophilic (charge separated) state. This case study suggests that catalysts featuring reversible dynamics can be advantageous relative to their structurally static counterparts.