New derivatives of strained, redox-active 9,10-bis(l,3-dithiol-2-yiidene)- 9,10-dihydroanthraeene systems

Abstract

The synthesis of new derivatives of 9,10-bis(l,3-dithiol-2-yHdene)-9,10- dihydroanthracene has been achieved by three general routes. A variety of Homer- Wadworth-Emmons reagents have been prepared from the corresponding 1,3-dithiolium cations; these have been shown to react in moderate yields to generate novel derivatives of the parent system. Alternative routes have also been developed for the preparation of unsymmetrical compounds, which were unattainable by Homer-Wadsworth-Emmons reagents. This was achieved via an addition/elimination reaction and provided unsuccessful route to unsymmetrical derivatives. The use of lithiation chemistry has been extensively developed providing a direct route to a broad range of functionalities. This methodology has paved the way to a new range of crown ethers and sterically strained cyclophanes, some of which have been extensively studied by cyclic voltammetry and X- ray crystallography. Solution electrochemistry of the 9,10-bis(l,3-dithiol-2-yHdene)-9,10- dihydroanthracene system displayed three redox waves, representing sequential formation of the dication, radical trication and tetracation species in an E(_q)E(_q)E(_q) process. Detailed single crystal X-ray crystal studies have been performed on the neutral compounds and a TCNQ charge transfer complex. The neutral molecule adopts a saddle like conformation; the bis(l,3-dithiole)benzoquinone system is U-shaped through an 'accumulating bend' comprising the boat conformation of the central (quinonoid) ring and folding of both 1,3-dithiole rings to generate a molecular cavity. Upon oxidation to the dication, the system becomes planar and aromatic with loss of the saddle shaped cavity. The development of this system as a potential sensor for metal cations has also been investigated.