Regioselective Catenation of Dinuclear Palladium and Platinum Metallocycles Promoted by π···π Interactions

Dinuclear metallocycles were assembled from an L-shaped bidentate ligand based on 4,4′-bipyridine and palladium or platinum square-planar cis complexes. The palladium (4a,b) or platinum (5a,b) square metallocycles were obtained as 1:1 regioisomeric mixtures depending on which pair of coordinative nitrogen atoms binds to the metal center. The squares display a π-deficient cavity suitable to incorporate two π-donor aromatic systems. Therefore, the reaction with macrocyclic polyethers (BPP34C10 or DN38C10) resulted in the regioselective self-assembly of the [3]catenanes 4a(BPP34C10 or DN38C10)2·6PF6 and 5a(BPP34C10 or DN38C10)2·6PF6 because only macrocycles 4a and 5a present the correct disposition of the π-deficient aromatic systems to maximize the π···π stacking interactions. Single-crystal X-ray analyses of [3]catenanes revealed that the structures are additionally stabilized by [C−H···O], [N−H···O] bonds and [C−H···π] interactions. The 1:2 inclusion complexes of metallocycles were prepared by self-assembly of three components: the ligand 1-(4-(pyridin-4-yl)benzyl)-4,4′-bipyridin-1-ium, a square planar complex M(en)(NO3)2 (M = Pd or Pt, en = ethylenediamine), and a dioxoaromatic guest in a 2:2:2 ratio. The comparative study of the formation of 1:2 inclusion complexes has allowed us to conclude that the π···π interactions between the host and guests are responsible for the observed regioselectivity.