Amphiphilic Polymer Hydrogel-supported Catalysts: Tuning the Accessibility to the Catalytic Site by Molecular Jacketing

Crosslinked amphiphilic hydrogels, prepared using a peripherally clickable hyperbranched polyester (HBP) and PEG-diazides of different molecular weights, were used to ligate Cu utilizing the triazole rings formed by the alkyne-azide click reaction. Since only a fraction of the peripheral propargyl groups in the HB polyester are needed to generate the crosslinked polymer, the remaining were clicked with different types of azides, such as MPEG azide, decyl azide or 4-methylbenzyl azide, to create a molecular jacket around the catalytic sites that can potentially influence the catalytic activity and reaction outcome. The crosslinked films ligated with Cu functioned very effectively to catalyse alkyne-azide click reactions, both in water and in organic solvents; the nature of the molecular jacket around the catalytic site had a clear influence the reaction rate, which depended upon the relative solubilities of the reactants. The gel-supported catalyst films were reused multiple times with little loss in catalytic activity.