Chemical mustard containment using simple palladium pincer complexes: the influence of molecular walls

Six amide-based NNN palladium(II) pincer complexes Pd(L)(CH3CN) were synthesized, characterized, and examined for binding the sulfur mustard surrogate, 2-chloroethyl ethyl sulfide (CEES). The complexes all bind readily with CEES as shown by (1)H NMR spectroscopy in CDCl3. The influence of para-substituents on the two amide phenyl appendages was explored as well as the effect of replacing the phenyl groups with larger aromatic rings, 1-naphthalene and 9-anthracene. While variations of the para-substituents had only a slight influence on the binding affinities, incorporation of larger aromatic rings resulted in a significant size-related increase in binding, possibly due to increasing steric and electronic interactions. In crystal structures of three CEES-bound complexes, the mustard binds through the sulfur atom and lies along the aromatic walls of the side appendages approximately perpendicular to the pincer plane, with increasingly better alignment progressing from phenyl to 1-naphthalene to 9-anthracene.