Preparation of Multi-Spin Systems: A Case Study of Tolane-Bridged Verdazyl-Based Hetero-Diradicals

Abstract

Iodine- and ethynyl-containing 'Kuhn'-verdazyls, oxoverdazyls, and nitronyl nitroxides were investigated as building blocks for the preparation of multi-spin systems via the Sonogashira reaction, and, as a result, eleven diradicals were prepared with fair yields. The reactivity of the building blocks indicates that oxoverdazyl iodides are effective starting components for the synthesis of diradicals via the Sonogashira coupling. The described one-step protocol allows combining different spin units, thereby facilitating the design of tolane-bridged diradicals and screening of their properties. The novel compounds were characterized by cyclic voltammetry, UV/Vis and electron spin resonance (ESR) spectroscopy. Although the electrochemical investigation and electronic spectra showed a negligible influence of radical moieties on each other, ESR data revealed a strong exchange interaction between two unpaired electrons. The prepared verdazyl-nitronylnitroxide diradicals have high stability at storage and hold promise for further investigation and application.