A new ferrocene-containing charge-transfer salt, (TTF)2(Fe(C5H4-CH(CH3)NHCOCH2SO3)2)

A novel ferrocene-containing dianion, Fe(C5H4-CH(CH3)NHCOCH2SO3 – )2 (1), has been prepared. The oxidation potential of the PPh4 salt is +0.35 V (vs. SCE in PhCN), indicating that it is a stronger donor than TTF (tetrathiafulvalene) by +0.03 V. The dianion provided a TTF salt, the structure and physical properties of which are reported. Over the past three decades a growing subject in the field of organic conductors is the design and development of multifunctional conductors. A variety of properties have been investigated such as magnetic [1,2], optically active [3], proton-conductive [4,5], chiral [6-10] and ferroelectric [11-13] conductors, which may display new phenomena where an interplay between conductivity and the other property plays a crucial role. The cation form of the ferrocenyl moiety shows so wide a variety of magnetic properties [14] and many researchers have tried introducing the ferrocenyl moiety into organic donor or acceptor molecules [15-20]. However, the resultant charge-transfer salts have not yet shown high electrical conductivity, probably because the bulky ferrocenyl groups prevent close approach of donor or acceptor molecules. In fact the highest value reported thus far is 7  10 -3 S/cm [19]. For more than seven years we have focused on preparing ferrocene-containing anions to use as counterions in organic conductors. So far, we have reported three TTF [21] and three bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) salts [22-24], one of which,  ́ ́-(BEDT-TTF)4(Fe(C5H4-CONHCN2SO3)2·H2O [23], shows metallic behavior down to 70 K with RT = 40 S/cm, which is the highest value for any ferrocene-containing organic conductors. However, for all these salts the ferrocenyl parts are neutral and therefore diamagnetic. It is speculated that this is probably because the oxidation potentials of all anions we have prepared so far are lower than TTF or BEDT-TTF (Chart 1). In fact, the cyclopentadienyl (Cp) rings of the ferrocenyl anionic moieties are substituted with electron-withdrawing carbonyl or sulfonate groups, which reduce their oxidation potentials. Therefore, preparation of anions having a lower oxidation potential is required. In this communication, we introduce a new ferrocene-containing dianion, Fe(Cp-CH(CH3)NHCOCH2SO3 – )2), 1, in which each Cp ring is substituted by an electron-donating methylmethilene group. The anion has provided a TTF salt, the structures and properties of which are reported. CONHCH2SO3 Ğ CONHCH2SO3 Ğ Fe SO3 Ğ SO3 Ğ Fe CONHCH2SO3 Ğ Fe CHNHCOCH2SO3 Ğ CHNHCOCH2SO3 Ğ Fe CH3 CH3 CpFeCp-CONHCH2SO3 Ğ Fe(Cp-CONHCH2SO3 )2 Fe(Cp-SO3 )2 1 S S