Stable, yet “naked”, azo radical anion ArNNAr− and dianion ArNNAr2− (Ar = 4-CN-2,6-iPr2-C6H2) with selective CO2 activation

Abstract

Azo radical anion 1˙⁻ and dianion 1²⁻ have been isolated by one- and two-electron reduction of the azo compound 1 (ArNNAr, Ar = 4-CN-2,6-ⁱPr₂-C₆H₂) with alkali metals, respectively. The reduced species have been characterized by single-crystal X-ray analysis, EPR, UV and FT-IR spectroscopy, as well as SQUID measurements. The filling of one and two electrons in the π* orbital of the N–N double bond of 1 leads to a half-double N–N bond in 1˙⁻ and a single N–N bond in 1²⁻. The uncoordinated nature of these reduced species enables them to activate CO₂. The exposure of 1˙⁻ solution to CO₂ led to the formation of oxalate anion C₂O₄²⁻, while that of 1²⁻ solution to CO₂ afforded the hydrazine dicarboxylate dianion [1-2CO₂]²⁻, which reversibly dissociated back to 1 and CO₂ upon oxidation.