Palladium(II) complexes of the chiral pinBPI ligand

Abstract

The chiral bis(pyridylimino)isoindoline derivative 5 (pinBPI) was prepared from the chiral pool reagent α-pinene 1 in three steps and an overall yield of 12%. Upon treatment with palladium(II) acetate and palladium(II) chloride, pinBPI 5 forms the nonracemic chiral complexes [(pinBPI)Pd(OAc)] 6 and [(pinBPI)PdCl] 7, respectively, as the only isolated species in good yield. The synthesis of a related thiazole-based ligand failed for the incompatibility of the four-membered carbocycle of the pinene subunit with the conditions of the thiazole-forming reaction. Both pinBPI chelates crystallize in chiral space groups but with different molecular conformations and intermolecular interactions. A triclinic system with space group P1 is found for the acetato derivative 6 which organizes pseudosymmetrically as a chloroform solvate with one helical and one (almost) planar molecule in the asymmetric unit. The chloro derivate 7 on the other hand crystallizes in the monoclinic space group P2 1 with Z = 8 and four independent molecules in the unit cell. Here, all molecules are in a pseudoplanar configuration with convex ligand conformations, but differ significantly in bond lengths and angles. The structures unravel two different possible scenarios for intermolecular association of such chiral BAI ligands.