Abstract
The incorporation of reactive functional groups onto the exterior of metal-organic cages (MOCs) opens up new opportunities to link their well-defined scaffolds into functional porous solids. Amine moieties offer access to a rich catalogue of covalent chemistry; however, they also tend to coordinate undesirably and interfere with MOC formation, particular in the case of Cu2 paddlewheel-based MOCs. We demonstrate that tuning the basicity of an aniline-functionalized ligand enables the self-assembly of a soluble, amine-functionalized Cu4L4 lantern cage (1). Importantly, we show control over the coordinative propensity of the exterior amine of the ligand, which enables us to isolate a crystalline, two-dimensional metal-organic framework composed entirely of MOC units (2). Furthermore, we show that the nucleophilicity of the exterior amine of 1 can be accessed in solution to generate a cross-linked cage polymer (3) via imine condensation.
Highlights
The applications of metal-organic frameworks (MOFs) have been rapidly expanding, with recent studies utilizing MOFs as crystallization matrices (Bloch et al, 2015), sacrificial scaffolds for hierarchical porosity (Dang et al, 2017; Haase et al, 2020), and protective agents in biomedicine (Yang and Yang, 2020; Liang et al, 2021)
The synthesis of L2 began with a Sonogashira cross-coupling between 2fluoro-1,3-diiodo-5-nitrobenzene (4) and methyl 3-ethynylbenzoate (5)
In summary we have reported the synthesis, crystallisation and post-assembly cross-linking of a soluble, amine-functionalised Cu4L4 metal-organic cages (MOCs) (1). 1 could be isolated in its discrete form both in solution and the solid-state
Summary
The applications of metal-organic frameworks (MOFs) have been rapidly expanding, with recent studies utilizing MOFs as crystallization matrices (Bloch et al, 2015), sacrificial scaffolds for hierarchical porosity (Dang et al, 2017; Haase et al, 2020), and protective agents in biomedicine (Yang and Yang, 2020; Liang et al, 2021). Compatibility of M2 paddlewheel-based MOCs with various surface functionalities These include coordinatively competitive groups such as hydroxyl (Niu et al, 2015), carboxylate (Albalad et al, 2019), carbonyl (Bloch et al, 2020), and amine substituents (Albalad et al, 2019; Schneider et al, 2020; Taggart et al, 2020) which can be installed onto the MOC exterior through ligand design or post-assembly modifications (Zeng et al, 2020). The work described sheds light on the chemistry of amine-functionalized MOCs and their utilization in the synthesis of cage-based polymeric solids (Figure 1)
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