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.

Platform for High-Spin Molecules: A Verdazyl-Nitronyl Nitroxide Triradical with Quartet Ground State

“…* Monoradical precursor I-Vrd-I upon crystallization from various solvents gives tightly intertwined fineneedle crystals. The crystals were too thin, not suitable for single crystal X-ray study.In crystalline paramagnets I-Vrd-NN and NN-Vrd-NN, bond lengths in the NN and Vrd parts are close to the average values reported for these types of radicals 41,42. The Vrd and phenyl rings arenearly planar.…”

“…In crystalline paramagnets I-Vrd-NN and NN-Vrd-NN, bond lengths in the NN and Vrd parts are close to the average values reported for these types of radicals. 43,44 The Vrd and phenyl rings are nearly planar. The imidazoline rings have a The I-Vrd-NN diradical crystallizes as a 1:1 solvate with acetone in the triclinic P-1 space group.…”

The syntheses, structures and spectroelectrochemical properties of 6-oxo-verdazyl derivatives bearing surface anchoring groups

“…2). These latter reactions represent rare examples of the direct modification of the verdazyl sub-structure by cross-coupling reactions, 17 and we believe compounds 8, 9 and 10 to be the first examples of verdazyl derivatives with ethynyl moieties conjugated to both 1-and 5-positions.…”

“…13 These potential applications have prompted renewed interest in the synthetic chemistry associated with verdazyl-based structures, 14,15 including demonstrations of Sonogashira cross-coupling reactions that have been used to extend the conjugation of aryl groups at either the 1-or 3-positions. 16,17 More generally, radical molecular species have been identified as exceptionally promising compounds for use in the development of the field of molecular electronics. [18][19][20][21][22][23] The incorporation of a molecular system featuring an unpaired electron within an electrode | molecule | electrode junction leads to a host of fascinating electronic properties, 24 including enhanced rectification, 25 spin-gating, 26 Kondo effects, 27 magnetoresistive effects 28 and quantum interference, 29 whilst the redox-activity of such systems allows for an exciting range of electrochemically gated applications.…”

Ferromagnetically Coupled S=1 Chains in Crystals of Verdazyl‐Nitronyl Nitroxide Diradicals

“…[3,5] In the course of our challenging research program, we tried to create anew type of p-conjugated diradicals containing nitronyl nitroxide (NN) and verdazyl moieties.For the preparation of these diradicals, we applied Sonogashira coupling of iodophenyl-and ethynylphenyl-substituted radical blocks and successfully isolated several tolane-bridged diradicals with N-linked "Kuhn"verdazyl or oxoverdazyl and NN moieties ( Figure 2). [6] Figure 1. Examples of stable triplet diradicals with large energy gaps DE ST and their hydrocarbon diradical prototypes.…”