New Benzo-9-Crown-3 Functionalized Aryl Imides for the Capture and Release of Lithium Ions from Solution

With an increased demand for lithium ion (Li-ion) battery technologies, and the small number of lithium mines around the globe, there has been a heightened desire to develop new materials capable of extracting lithium from aqueous sources such as the ocean. To do so in an economically viable way, the materials must be highly selective toward the extraction of Li-ions so as not to necessitate the further purification from competing metal ions such as magnesium, sodium, or calcium. To address this, herein we report on three new conjugated imide compounds functionalized with the crown ether benzo-9-crown-3. The three new compounds Phth-CE, F-Phth-CE, and NMI-CE were synthesized via atom-economical condensation reactions between an amino functionalized benzo-9-crown-3 with commodity aryl imide building blocks. These three new compounds serve to develop an understanding of Li-ion capture via the benzo-9-crown-3 moieties scaffolded onto stable aromatic ring systems. The nodal plane between the aryl imide and the phenyl ring of benzo-9-crown-3 isolates the crown ether allowing for unhindered Li-ion capture and release. Subtle derivatization of the aryl imide showcases structural versatility to include a fluoride amenable to nucleophilic aromatic substitution and/or to act as a diagnostic handle and naphthalene unit extending optical absorption to longer wavelengths. Each new compound exhibits the formation of Li-ion sandwich complexes as determined by ⁷ Li NMR spectroscopy, and near identical Li-ion extraction efficiencies, distribution coefficients, and selectivity under acidic conditions in neat and mixed-metal ion solutions as determined by triple quadrupole inductively coupled plasma mass spectrometry analysis.