Exploiting Supramolecular Interactions to Control Isomer Distributions in Reduced-Symmetry [Pd2L4]4+ Cages

• Published in: Inorganic chemistry Vol. 62; no. 5; pp. 1833 - 1844
• Main Authors: Vasdev, Roan A. S., Preston, Dan, Casey-Stevens, Caitlin A., Martí-Centelles, Vicente, Lusby, Paul J., Garden, Anna L., Crowley, James D.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 06.02.2023
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.2c00937

High-symmetry metallosupramolecular architectures (MSAs) have been exploited for a range of applications including molecular recognition, catalysis, and drug delivery. Recently, there have been increasing efforts to enhance those applications by generating reduced-symmetry MSAs. Here we report our attempts to use supramolecular (dispersion and hydrogen-bonding) forces and solvophobic effects to generate isomerically pure [Pd2(L)4]4+ cage architectures from a family of new reduced-symmetry ditopic tripyridyl ligands. The reduced-symmetry tripyridyl ligands featured either solvophilic polyether chains, solvophobic alkyl chains, or amino substituents. We show using NMR spectroscopy, high-performance liquid chromatography, X-ray diffraction data, and density functional theory calculations that the combination of dispersion forces and solvophobic effects does not provide any control of the [Pd2(L)4]4+ isomer distribution with mixtures of all four cage isomers (HHHH, HHHT, cis-HHTT, or trans-HTHT, where H = head and T = tail) obtained in each case. More control was obtained by exploiting hydrogen-bonding interactions between amino units. While the cage assembly with a 3-amino-substituted tripyridyl ligand leads to a mixture of all four possible isomers, the related 2-amino-substituted tripyridyl ligand generated a cis-HHTT cage architecture. Formation of the cis-HHTT [Pd2(L)4]4+ cage was confirmed using NMR studies and X-ray crystallography.