Nickel Bis(dithiolene) Complexes and Tetrathiafulvalenes from Sterically Hindered Di- and Tetra-Substituted Dithiine-dithiolo-thione Precursors

Three variants of 5,6-dihydro-1,4-dithiin-2,3-(1’,3’-dithiole-2’-thione) (dddt) bearing up to four substituents on the ethylene bridge have been obtained by hetero-Diels-Alder reaction. The substituted dddt derivatives have the advantage of providing modulation of the steric hindrance and stereogenic centres, and represent valuable intermediates for both tetrathiafulvalene (TTF) and metal-dithiolene complexes. Within this work, disubstituted and tetrasubstituted dddt derivatives have been used for the synthesis of Ni(II) monoanionic and neutral complexes, as well as for tetra- and octa-methylated EDT-TTF and BEDT-TTF (EDT=ethylenedithio, BEDT=bis(ethylenedithio)) derivatives. While the influence of the bulkiness and number of the substituents is observed in the solid state packing of both types of materials (complexes and TTF), the absence of the counterion in the case of the neutral complexes translated into increased intermolecular interactions between the donors and the formation of 1D and 2D layers. The two examples of tetrasubstituted TTF radical cation salts reported in here show semiconducting behaviour due to the formation of dimers and lateral interactions through the S atoms. Our findings highlight the importance of substitution on these type of dddt precursors and their potential for electroactive molecular materials.