Tetrathiafulvalene Derivatives Linking a Dichalcogenolane Ring through the σ-Bond: New Donor Components for Organic Metals

A synthetic study of the dioxolane derivatives of methylenedithio(ethylenedithio)tetrathiafulvalene (MET), bis(methylenedithio)tetrathiafulvalene (MT), and methylenedithiotetrathiafulvalene, their dithiolane analogues, and the oxathiolane derivative of MET
has been undertaken to explore new organic metals. A practically useful preparation of the
biheterocycle-fused 1,3-dithiol-2-ones as building blocks for these dichalcogenolane-linked
tetrathiafulvalene (TTF) donors has been realized via the newly developed BF3-promoted
reactions. The effect of the additional linked dichalcogenolane ring on the electron-donating
ability is investigated by cyclic voltammetry. An X-ray crystallographic analysis of the
oxathiolane-linked MET reveals that its molecular structure is isostructural with that of
its dithiolane analogue but not bulkier than that of its dioxolane analogue. Several of the
present TTF donors have produced metallic charge-transfer materials, two of which are
characterized by X-ray crystallography. In the crystal structure of the 7,7,8,8-tetracyanoquinodimethane complex of the dioxolane-linked MT that exhibits metallic-like behavior
around room temperature, the donor molecules are stacked head-to-tail to form the dimers,
which are connected by C−H···O hydrogen bonds. On the other hand, in the metallic AsF6
salt of the dioxolane-linked MET stable down to 2.0 K, the donor molecules are stacked
head-to-head to form two-dimensional sheets despite the dioxolane ring being perpendicularly
attached to the MET molecule.