Evaluation of polyketones with N-cyclic structure as electrode material for electrochemical energy storage: case of tetraketopiperazine unit

Pursuing the electrochemical evaluation vs. Li of carbonyl-based cyclic structures deriving from the oxocarbon family, polyketones with N-cyclic structure are investigated to probe the potential modifications. In this communication, we specifically report on the electrochemical investigation of our first selected family of heterocycles based on the 2,3,5,6-tetraketopiperazine unit. Working in a systematic way, a series of tetraketopiperazine molecules with quite different R groups as substituents (i.e., phenyl, allyl and propyl functions) have been synthesized and characterized. Such small molecules were found to rapidly solubilise in commonly used electrolytes. To bypass this issue, we have prepared an oligomeric form via acyclic diene metathesis (ADMET). Preliminary results on the poly-N,N'-diallyl-2,3,5,6-tetraketopiperazine oligomer show a sustained reversible capacity of 110 mAh g(-1) at near 2.45 V. The insight gained from this work is the fact that two intracyclic nitrogen atoms or a lithiated ene-diolate functionality in the C-6-based polyketone cyclic structure induces a similar tuning of the redox potential.