A Palladium(II) Complex of a C4 Chelating Bis(NHC) Diphosphonium Bis(ylide) Ligand

The preparation and the structure of a palladium(II) complex bearing an extremely electron rich C-4 chelating bis(NHC) diphosphonium bis(ylide) ligand are described. This Pd complex is obtained as a single diastereoisomer via a four-step synthesis from the bis(imidazol-1-yl)methane in 43% overall yield. It results from two fully selective processes: the deprotonation of two imidazolium moieties in the presence of phosphonium centers and the coordination of two phosphonium ylides at the metal center. Steric and electrostatic constraints between the triphenylphosphonio substituents at the C-ylidic positions are proposed to explain the diastereoselectivity of the C-2 coordination in favor of the dl form (RR/SS).