A chiral [2]catenane self-assembled from meso-macrocycles of palladium(ii)

Abstract

Reaction of trans-[PdX₂(SMe₂)₂] (X = Cl or Br) with the chiral ligand LL = 1,1′-binaphthyl-2,2′-(NHC( = O)-3-C₅H₄N)₂ gave the [2]catenane complexes trans-[{(PdX₂)₂(µ-LL)₂}₂], which are formed by self-assembly from 4 units each of trans-PdX₂ and LL. The catenation is favored by the formation of multiple hydrogen bonds between the constituent macrocycles (4 × NH⋯ClPd, 2 × NH⋯OC). If the ligand LL is racemic, each macrocycle trans-[(PdX₂)₂(µ-LL)₂] is formed in the meso form trans-[(PdX₂)₂(µ-R–LL)(µ-S–LL)] but the resulting [2]catenane is chiral as a direct result of the catenation step. This is the first time that this form of chiral [2]catenane has been observed. The enantiomers of the [2]catenane further self-assemble in the crystalline form, through secondary intermolecular Pd⋯X bonding, to form a racemic infinite supramolecular polymer of [2]catenanes.