Shapeshifting Ligands\nMask Lewis Acidity of Dicationic\nPalladium(II)

Supporting ligands limit the degree\nof electrophilic\nactivation\nfor any substrate because they also reduce the Lewis acidity of the\ntransition metal ion. Here, we temporarily mask the Lewis acidity\nof dicationic Pd(II) by using “shapeshifting” bidentate\npyrimidine/olefin ligands <b>L1</b> and <b>L2</b>. These\nligands delocalize/relocalize charge via reversible C–N bond\nformation. So, although ligated dicationic Pd compounds [<b>1</b>]<sup>2+</sup> and [<b>2</b>]<sup>2+</sup> appear charge separated\n(distributed across Pd and ligand), they react comparably to a solvated\nPd(II) dication. Despite reacting like strong Lewis acids, the complexes\nare tolerant of polar functional groups (Lewis bases that often inhibit\nelectrophilic catalysis). We propose that this property originates\nfrom the installation of a more nucleophilic (charge separated) state.\nThis case study suggests that catalysts featuring reversible dynamics\ncan be advantageous relative to their structurally static counterparts.