Tetrachalcogenafulvalenes

G.C.Papavassiliou, A.Terzis, P.Delhaes. Tetrachalcogenafulvalenes, Metal 1,2-Dichalcogenolenes and Their Conducting Salts. In Handbook of Organic Conductive Molecules and Polymers. Vol. 1. Edited by H.S.Nalwa. John Wiley and Sons Ltd., 1997. ch. 

Scheme 2 Known tetrachalcogenafulvalene systems containing selenium or tellurium...

The mode of packing of (10) was quite unexpected when compared with those of other tetrachalcogenafulvalenes. The packing of (10) was in a zigzag chain arrangement of adjacent molecules with neighboring chains approximately perpendicular the other tetrachalcogenafulvalenes have parallel chains. 

The electrochemical oxidation potentials of various tetrachalcogenafulvalenes are compiled in Table 13. As the size of the heteroatom increases, the gap between Z71/2 for the first oxidation potential and iJ1/2 for the second oxidation potential narrows. This is presumably due to more localization of the radical cation on the heteroatom lone pairs. As the size of the heteroatoms increases, overlap with the adjoining rr-framework becomes less efficient. 

Table 13 Electrochemical Oxidation Potentials of Tetrachalcogenafulvalenes at a Platinum Electrode...

Thermolyses of l,3-dichalcogenole-2-thiones and -2-selenones lead formally to carbenes by loss of elemental sulfur and selenium, respectively. These species dimerize to produce 1,4,5,8-tetrachalcogenafulvalenes (Scheme 6). In practice this transformation is carried out in the presence of a sulfur scavenger such as a phosphite or phosphine. Examples of this transformation are compiled in Table 14. 

Scheme 6 Thermolyses of l,3-dichalcogenole-2-thiones and -2-selenones to give tetrachalcogenafulvalenes...

No class of donor molecules has played a more important role in organic conductor research than the tetrachalcogenafulvalenes (1). In fact, all known... 

Tetrachalcogenafulvalenes and their charge-transfer complexes as organic conductors 87MI61, 87YGK502 89PS(43)187. 

The conducting properties of tetrachalcogenafulvalenes have already been treated in Section 4.14.4.1 as well as in CHEC(1984) and CHEC-II(I996). Moreover, the review articles cited in Section 4.I4.I provide an overview of this application. 

A tetrachalcogenafulvalene can be oxidized in two discrete steps, each step giving rise to a Huckel-type [4n -I- 2] aromatic delocalized r-system, thus for tetraselenafulvalene (TSF) (7), Scheme 2 results. 

Comprehensive reviews covering the electrochemical data for selenium- and tellurium-based tetrachalcogenafulvalenes have appeared, as mentioned in the introduction <87SR155,93SR245). Table 2 gives the half-wave oxidation potentials for selected representative examples of the selenium- and tellurium-based donors. 

Scheme 3 shows the sulfur- and selenium-based tetrachalcogenafulvalenes, which have given rise to superconducting radical cation salts. It is worth noting from this list, that there are almost as many selenium- as sulfur-based systems that have shown superconductivity, such as (DMET)2Au(CN)2 (9)... 

CL93l> albeit the number of TTF derivatives which have been investigated is many times larger than the number of TSF derivatives <91SCII50l>. Table 3 gives a compilation of the Tc temperatures for the tetrachalcogenafulvalene salts (selenium and mixed sulfur-selenium-based systems) which have shown superconductivity. 

Table 2 Half-wave oxidation potentials for selected tetrachalcogenafulvalenes.

The formyl group in the tetrachalcogenafulvalene system (131) reacts in the normal way, thus borohydride reduction gives access to the corresponding hydroxymethyl-substituted fulvalene (132) in excellent yield (Equation (10)) <89cci520,93SM1978, 93SM2073). 

Aspects of the application of a number of 1,3-dichalcogenole systems and especially the corresponding fulvalenes have already been mentioned in Section 3.14.4.1. Scheme 3 gives a compilation of the presently known sulfur and selenium tetrachalcogenafulvalenes which have given rise to... 

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