Dynamic palladium coordination cages formed by self-assembly of extended tetra(nitrile)cavitands

Abstract

Two extended tetra(4-cyanophenylethynyl)cavitands with methylene (6S) and ethylene (6L) bridges were synthesized for coordination-driven self-assembly. Reaction with Pd(dppp)(OTf)₂ in a 2 : 4 ratio afforded discrete, symmetric coordination cages (8S and 8L), characterized by NMR, IR and DOSY. The assemblies exhibit dynamic behavior that is dependent on concentration, with intermediate species identified through NMR titration studies. No cage formation was observed with Pt(II) or Ni(II) analogues, highlighting the importance of the kinetic lability of Pd(II) species, the size of the metal center and the geometry of the dppp ligand.