Post-synthetic Mannich chemistry on metal-organic frameworks: system-specific reactivity and functionality-triggered dissolution

Amer Hamzah, Harina and Gee, William J. and Raithby, Paul R. and Teat, Simon J. and Mahon, Mary F. and Burrows, Andrew David (2018) Post-synthetic Mannich chemistry on metal-organic frameworks: system-specific reactivity and functionality-triggered dissolution. Chemistry - A European Journal, . ISSN 0947-6539. (doi:https://doi.org/10.1002/chem.201801419) (Access to this publication is currently restricted. You may be able to access a copy if URLs are provided)

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Abstract

The Mannich reaction of the zirconium MOF [Zr6O4(OH)4(bdc-NH2)6] (UiO-66-NH2, bdc-NH2 = 2-amino-1,4-benzenedicarboxylate) with paraformaldehyde and pyrazole, imidazole or 2-mercaptoimidazole led to post-synthetic modification (PSM) through C–N bond formation. The reaction with imidazole (Him) goes to completion whereas those with pyrazole (Hpyz) and 2-mercaptoimidazole (HimSH) give up to 41% and 36% conversion, respectively. The BET surface areas for the Mannich products are reduced from that of UiO-66-NH2, but the compounds show enhanced selectivity for adsorption of CO2 over N2 at 273 K. The thiol-containing MOFs adsorb mercury(II) ions from aqueous solution, removing up to 99%. The Mannich reaction with pyrazole succeeds on [Zn4O(bdc-NH2)3] (IRMOF-3), but a similar reaction on [Zn2(bdc-NH2)2(dabco)] (dabco = 1,4-diazabicyclo[2.2.2]octane) gave [Zn3(bdc-NH2)1.32(bdc-NHCH2pyz)1.68(dabco)]·2C7H8 5, whereas the reaction with imidazole gave the expected PSM product. Compound 5 forms via a dissolutionrecrystallisation process that is triggered by the 'free' pyrazolate nitrogen atom competing with dabco for coordination to the zinc(II) centre. In contrast, the 'free' nitrogen atom on the imidazolate is too far away to compete in this way. Mannich reactions on [In(OH)(bdc-NH2)] (MIL-68(In)-NH2) stop after the first step, and the product was identified as [In(OH)(bdc-NH2)0.41(bdc-NHCH2OCH3)0.30(bdc-N=CH2)0.29], with addition of the heterocycle prevented by steric interactions.

Item Type: Article
Uncontrolled keywords: metal-organic frameworks, post-synthetic modification, mercury sequestration
Divisions: Faculties > Sciences > School of Physical Sciences
Depositing User: William Gee
Date Deposited: 30 May 2018 08:59 UTC
Last Modified: 31 May 2018 08:37 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/67154 (The current URI for this page, for reference purposes)
Gee, William J.: https://orcid.org/0000-0002-6520-6216
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