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 1H 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.