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

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)(mu-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 x NH...ClPd, 2 x NH...O=C). If the ligand LL is racemic, each macrocycle trans-[ (PdX2)(2)(mu-LL)(2)] is formed in the meso form trans-[(PdX2)(2)(mu-R-LL)(mu-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.