“Dual Layer” Self-Sorting with Cucurbiturils

Abstract

Platinum(II) complexes bearing terpyridyl (tpy) and thiolate ligands were used to test the design of a “dual layer” self-sorting system in the presence of Cucurbit[8]uril (CB[8]). Pt(II) thiolates and CB[8] form 2:1 assemblies, with both metallic centers sitting on top of one another at one of the macrocycle portals. We showed that any pair of these CB[8]-secured Pt(II) complex dimers bearing different tpy “heads” and thiolate “tails” scrambles to afford up to 10 ternary assemblies via two processes: (1) supramolecular exchanges (i.e., the egression and ingression of Pt complexes from and into CB[8]) and (2) ligand exchanges between the Pt thiolates. The mixtures of 10 assemblies were fully characterized by nuclear magnetic resonance spectroscopy. While the thiolate tails do not significantly affect the rate of the supramolecular exchanges, they were found to control (1) the kinetics of ligand exchange, with bulkier thiolates causing dramatic rate retardations, as well as (2) the thermodynamics of the self-sorting process, i.e., the distribution of assemblies at equilibrium, via intra-CB[8] assembly interactions between pairs of thiolates. Ligand exchanges are consistently slower than supramolecular exchanges. An associative pathway that involves the formation of dimers of CB[8]-secured Pt dimers (a total of 4 Pt complexes) during the ligand exchange process was invoked to rationalize the observed kinetics.