Unexpected reversal of reactivity in organic functionalities when immobilized together in a metal-organic framework (MOF)

A pillared, mixed-ligand metal-organic framework (MOF) material composed of both amine- and hydroxyl-bearing linkers was incubated with a variety of isocyanates for reaction. The hydroxyl groups were converted to the corresponding carbamates to a greater extent than the amines were converted to the corresponding ureas. The apparent superior reactivity of the hydroxyls conflicts with the relative nucleophilicities previously observed for the reactions of these functionalities with other electrophiles in the same MOF. When the reactive linkers were immobilized individually in monofunctional MOFs, the amine-functionalized linker was more reactive than the hydroxyl-bearing linker. This result indicates that the reversal in reactivity observed for isocyanates is due to the confinement of the two functionalities together within the MOF pores.