Post-Synthetic Modification of Zr-Metal-Organic Frameworks through Cycloaddition Reactions

Cycloaddition reactions are highly attractive for post-synthetic modification of metalorganic frameworks (MOFs). We report herein on cycloaddition reactions with PIZOF(R1,R2)s, which are porous interpenetrated Zr-based MOFs with Zr6O4(OH)4(CO2)12 as the nodes and the dicarboxylates -O2C[PE-P(R1,R2)-EP]CO2- (P: phenylene, E: ethynylene; R1, R2: side chains at the central phenylene unit) as the linkers. 1,3-Dipolar cycloaddition between the pendant ethyne moieties of PIZOF(OMe,OCH2C?CH) and 4-methylbenzyl azide resulted in 98?% conversion of the ethyne groups. Reactions of PIZOF(OMe,O(CH2)3furan) with maleimide, N-methylmaleimide, and N-phenylmaleimide converted 98, 99, and 89?% of the furan moieties into the DielsAlder adducts. However, no reaction occurred with maleic anhydride. High-resolution 1H NMR spectra were crucial in determining the conversion and identifying the reaction products. Of all the reagents (NaOD/D2O, D2SO4, Bu4NF, CsF, CsF/DCl, and KHF2) tested for the disassembly of the PIZOFs in [D6]DMSO, the combination of CsF and DCl was found to be the best. The disassembly at room temperature was fast (515 min), and after the addition of K2CO3 the 1H 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.