Synthesis and click modification of an azido-functionalized Zr(iv) metal–organic framework and a catalytic study

Abstract

An azido-functionalized Zr(II) metal-organic framework (MOF), UiO-67-N 3 , was synthesized from 2-azidobiphenyl-4,4 0 -dicarboxylic acid. During the synthesis, the ligand can undergo in situ thermocyclization to give 9H-carbazole-2,7-dicarboxylic acid. It proved that UiO-67-N 3 can be obtained at relatively low temperature without ligand transformation. Post-synthetic modification of UiO-67-N 3 was successfully performed via the click reactions between the azido group and different alkyne compounds to produce new MOFs with different functionalities, UiO-67-Tz-X with X ¼ COOCH 3 , OH and NH 2 . These clicked MOFs, especially UiO-67-Tz-NH 2 , exhibit better stability than the mother material UiO-67-N 3 . The catalytic properties of the clicked MOFs were studied using the Knoevenagel condensation reactions between benzaldehyde and different methylene compounds. Only the NH 2 -functionalized MOF is active, suggesting that the amino group, rather than the triazole group or any other component of the framework, is the crucial active site. The catalysis is heterogeneous. The MOF is recyclable for the reaction with malononitrile but not for the reaction with ethyl cyanoacetate. The deactivation in the latter case is proposed to be because the amino site reacts with the ester group of ethyl cyanoacetate to form amide.

Postsynthetic Modification of Zirconium Metal‐Organic Frameworks

“…UiO‐67‐N 3 , which contains 2‐azidobiphenyl‐4,4′‐dicarboxylate, has been prepared, although the reaction temperature had to be reduced to 80 °C as conventional synthetic methods (140 °C) resulted in thermal cyclisation of the ligand to 9 H ‐carbazole‐2,7‐dicarboxylate in situ . This phenomenon also results in a poor thermal stability of the MOF, as thermal cyclisation results in a bent ligand geometry that cannot be accommodated by the framework, resulting in collapse of the overall network structure.…”

Synthesis and post-synthetic modification of amine-, alkyne-, azide- and nitro-functionalized metal–organic frameworks based on DUT-5

“…This transformation of H 2 azideBPDC has recently also been reported in literature when high temperatures (> 80 °C) were used during the synthesis of the Zr-based framework UiO-67. 58 The formation of the carbazole led to a slightly bent linker molecule and therefore a changed geometry, which might be the reason for the low crystallinity of the azide-containing MOFs. Nitrogen physisorption measurements were performed to determine the accessible pore volumes and specific surface areas.…”

Postsynthetic Modification of Metal‐Organic Frameworks through Click Chemistry

“…[36][37][38][39][40][41] Click chemistry, [42][43][44] which can proceed the reaction efficiently with high yields and high specificity in the presence of various functional groups, has received a great deal of use in different fields, for example, dendrimer synthesis [45,46] and surface science. More recently, Gao et al [57] reported another azide-MOF, which was subjected to PSM with different alkynes through click reaction and the resulting MOFs can be used as catalysts for Knoevenagel condensation reactions. [50][51][52][53][54][55] In this review, we will summarize the research progress of PSM of MOFs through click chemistry.…”