Post-synthetic modification of Zr-metal-organic frameworks through cycloaddition reactions

Abstract

Cycloaddition reactions are highly attractive for post-synthetic modification of metal-organic frameworks (MOFs). We report herein on cycloaddition reactions with PIZOF(R(1),R(2))s, which are porous interpenetrated Zr-based MOFs with Zr(6)O(4)(OH)(4)(CO(2))(12) as the nodes and the dicarboxylates (-)O(2)C[PE-P(R(1),R(2))-EP]CO(2)(-) (P: phenylene, E: ethynylene; R(1), R(2): side chains at the central phenylene unit) as the linkers. 1,3-Dipolar cycloaddition between the pendant ethyne moieties of PIZOF(OMe,OCH(2)C≡CH) and 4-methylbenzyl azide resulted in 98% conversion of the ethyne groups. Reactions of PIZOF(OMe,O(CH(2))(3)furan) with maleimide, N-methylmaleimide, and N-phenylmaleimide converted 98, 99, and 89% of the furan moieties into the Diels-Alder adducts. However, no reaction occurred with maleic anhydride. High-resolution (1)H NMR spectra were crucial in determining the conversion and identifying the reaction products. Of all the reagents (NaOD/D(2)O, D(2)SO(4), Bu(4)NF, CsF, CsF/DCl, and KHF(2)) tested for the disassembly of the PIZOFs in [D(6)]DMSO, the combination of CsF and DCl was found to be the best. The disassembly at room temperature was fast (5-15 min), and after the addition of K(2)CO(3) the (1)H NMR data were identical to those of the diacids (=protonated linkers) dissolved in pure DMSO. This allowed for simple structure elucidation through data comparison. CsF/DCl dissolves not only PIZOFs but also the hydrolytically very stable UiO-66.