Palladium(II) Cage Compounds Based on Diphenylglycoluril

Article abstract of DOI:10.1021/ja00209a027

A four-armed tetra-1-imidazolyl ligand (Lig) equipped with the concave framework of diphenylglycoluril (tetrahydro-3a,6a-diphenylimidazo<4,5-d>imidazole-2,5(1H,3H)-dione) has been designed to construct a host that contains a potentially catalytically active metal center in or close to a cavity.Reaction of Lig (arm = CH2(OCH2CH2)2Im) with Pd(CH3CN)2Cl2 results in the formation of a complex with the general formula Cl2.This complex has a cage structure that is unstable and collapses.The collapsed structure has either a left or a right twisted conformation.These conformations interconvert rapidly, the activation free energy of the process being 30 +/- 2 kJ.mol^-1.Ligands without oxygen atoms or only one oxygen atom per arm react with Pd(CH3CN)2Cl2 to afford cage complexes with the molecular formula Cl.The cages of these complexes do not collapse.The imidazolyl groups and the chloride ions are involved in a scrambling process in such a way that at any moment the Pd²⁺ ion is surrounded by three imidazolyl groups and one chloride ion.Data are presented suggesting that intramolecular H bonding is a driving force for cage collapse.