Abstract
Metalation of covalent organic frameworks (COFs) is a critical strategy to functionalize COFs for advanced applications yet largely relies on the pre-installed specific metal docking sites in the network, such as porphyrin, salen, 2,2′-bipyridine, etc. We show in this study that the imine linkage of simple imine-based COFs, one of the most popular COFs, readily chelate transition metal (Ir in this work) via cyclometalation, which has not been explored before. The iridacycle decorated COF exhibited more than 10-fold efficiency enhancement in (photo)catalytic hydrogen evolution from aqueous formate solution than its molecular counterpart under mild conditions. This work will inspire more functional cyclometallated COFs to be explored beyond catalysis considering the large imine COF library and the rich metallacycle chemistry.
Highlights
The designable ordered porous structure of covalent organic frameworks (COFs) has attracted broad research interest in the past decades.[1,2,3,4] COFs are completely composed of light elements, their advanced applications, catalysis,[5,6,7,8] have stressed the role of metal species anchored onto the network.[8,9,10] To accommodate the target metal, a building unit with a suitable metal binding site is required to be incorporated into the framework, which usually meets complicated organic synthesis
We show in this study that the imine linkage of simple imine-based COFs, one of the most popular COFs, readily chelate transition metal (Ir in this work) via cyclometalation, which has not been explored before
Immobilization of the catalyst on proper solid support is expected to extend the catalyst lifetime.[54]. Taking all of these considerations together, in this work, we show that cyclometalation at the imine site leads to an iridacycle functionalized imine COF for the rst time (Fig. 1C), which exhibits fascinating performance incatalytic hydrogen evolution reaction (HER) from aqueous formate solution
Summary
The designable ordered porous structure of covalent organic frameworks (COFs) has attracted broad research interest in the past decades.[1,2,3,4] COFs are completely composed of light elements (typically H, B, C, N, O, Si), their advanced applications, catalysis,[5,6,7,8] have stressed the role of metal species anchored onto the network.[8,9,10] To accommodate the target metal, a building unit with a suitable metal binding site is required to be incorporated into the framework, which usually meets complicated organic synthesis. Some iridium-based homogeneous HCOOH dehydrogenation catalysts displayed low stability and were prone to deactivate via nanoparticle formation.[52,53] Immobilization of the catalyst on proper solid support is expected to extend the catalyst lifetime.[54] Taking all of these considerations together, in this work, we show that cyclometalation at the imine site leads to an iridacycle functionalized imine COF for the rst time (Fig. 1C), which exhibits fascinating performance in (photo)catalytic HER from aqueous formate solution.
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