Stoichiometric Control of Guest Recognition of Self-Assembled Palladium(II)-Based Supramolecular Architectures

We report flexible [Pd(L)2]2+ complexes where there is self-recognition, driven by & pi;-& pi; interactions between electron-rich aromatic arms and the cationic regions they are tethered to. This self-recognition hampers the association of these molecules with aromatic molecular targets in solution. In one case, this complex can be reversibly converted to an 'open' [Pd2(L)2]4+ macrocycle through introduction of more metal ion. This is accomplished by the ligand having two bidentate binding sites: a 2-pyridyl-1,2,3-triazole site, and a bis-1,2,3-triazole site. Due to favourable hydrogen bonding, the 2-pyridyl-1,2,3-triazole units reliably coordinate in the [Pd(L)2]2+ complex to control speciation: a second equivalent of Pd(II) is required to enforce coordination to bis-triazole sites and form the macrocycle. The macrocycle interacts with a molecular substrate with higher affinity. In this fashion we are able to use stoichiometry to reversibly switch between two different species and regulate guest binding. Stoichiometry can be used in a flexible system to switch between a 2+2 [Pd2(L)2]4+ macrocycle and a [Pd(L)2]2+ compound where the uncomplexed arms occlude access to the cationic part of the molecule by guests. We can thereby controllably regulate affinity between our host and an aromatic guest.image

Automated summary

This article reports flexible [Pd(L)2]2+ complexes that show self-recognition driven by π-π interactions between electron-rich aromatic arms and the cationic regions they are tethered to. This self-recognition hampers the association of these molecules with aromatic molecular targets in solution. In one case, the complex can be reversibly converted to an 'open' [Pd2(L)2]4+ macrocycle through introduction of more metal ion.