Dithiafulvene Derivatives

2-Alkynyl alkanedithioates (49) yield dithiafulvenes (50) on treatment with bases, via diaIkylidene-l,3-dithioles. The indene derivative (51) and other dithiafulvenes, including isothiathiophthens (see Chapter 7), have been prepared by condensations involving 2-methylthio-l,3-dithiolmm salts. 

The mechanism of the base-catalysed decomposition of 4-aryl-1,2,3-selena-diazoles to diselenafulvenes has received detailed study. Several reports have appeared on the synthesis of benzodithiafulvenes, and the oxidation of dithia-fulvenes of type (52) has been investigated. The products are the red-violet salts (53), which form part of an interesting redox system. 

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Dithiafulvene derivatives behave as -electron donors and form stable charge-transfer complexes and radical ion salts with a wide variety of organic and inorganic acceptor species. 

Mechanically interlocked molecular compounds, including catenanes, rotax-anes, and carceplex, are constituted of molecules composed of two or more components that cannot be separated from each other [95-98]. The development of strategy for achieving controlled self-assembling systems by non-covalent interaction enables one to prepare such attractive compounds for applications in nanoscale molecular devices. The dithiafulvene derivatives are effective electron donors, which are good candidates to form those supramolecular systems with appropriate acceptors by virtue of intermolec-ular CT interactions. In this chapter, dithiafulvene polymers forming rotax-ane structures are especially described. 

It has been shown (64JHC163) that a-halo ketones readily form 1,3-dithioles with gem-dithiols. A convenient alternative pathway for the synthesis of certain l,3-dithiol-2-ylidene derivatives (295) is the reaction of a-halo ketones with dithioacids of type (294) which exist as a,(3-unsaturated gem-dithiols (65JOC732). For the synthesis of dithiafulvene derivatives via (4,5-diethoxycarbonyl-l,3-dithiolyl)tributylphosphonium tetrafluoroborate, see (79JOC930). 

Dithiafulvenes undergo attack by electrophiles at the exocyclic carbon to give 6-substituted derivatives (Scheme 1). 

A series of -conjugated poly(dithiafulvene)s (12) have been prepared by cycloaddition polymerization of aldothioketenes and their alkynethiol tautomers, which were derived from aromatic diynes (Scheme 3) [70-73]. Efficient expansions of -conjugation systems in the polymers were evident... 

There is a long standing interest in the chemistry and the properties of cyclic compounds containing sulfur atom in modern material chemistry due to their redox chemistry. In particular, the focus has been on dithiole derivatives, e.g., dithiafulvenes and tetrathiafulvalenes, since the finding of metallic conductivity and low temperature superconductivity in radical cation salts. The quite low oxidation potentials of 1,4-dithiin compounds have been reported, recently [109]. On the other hand, thioketene dimers (2,4-bis(alkyli-dene)-l,3-dithietane) have been known for more than 100 years and synthesized by various methods [110-115]. The structure of these dimer compounds is similar to that of the redox-active sulfur compounds therefore, the potential electronic property of the thioketene dimer moiety is considerably attractive with the aim of application to a new and better -donor. 

We have reported the first electroactivity of a thioketene dimer compound [116]. The CV measurement of 2,4-dibenzylidene-l,3-dithietane (31), which was prepared by a basic dimerization of phenylthioketene derived from ben-zyltriphenylphosphonium chloride, showed irreversible two-step oxidation peaks at 0.25 and 0.61 V vs Ag/Ag+, indicating that 31 acts as a stronger electron donor than 2,6-bisphenyl-l,4-dithiafulvene (30) and TTF (2). The dimer (31) can form a 1 1 CT complex with TCNQ in DMSO. Cycloaddition polymerization of bisthioketene derived from p-xylenebis(triphenylphosphoni-um chloride) gave a -conjugated polymer (32) with thioketene dimer unit in the main chain (Scheme 12). This polymer was the first polymer contain-... 

The trithione -methides (3-methylene-1,2-dithioles) are iso-77-electronic with the heptafulvenes,71 and possess a basicity comparable to that of the latter. Some true 3-alkylatSd 1,2-dithiolium salts can be obtained by protonation of compounds 52. This method of preparation is rather narrowly limited, however, by the fact that the simple derivatives of 52 (as in the hydrocarbon series) are evidently very unstable and have not as yet been described. These dithiafulvenes become stable, easily handled compounds only when they contain aryl or typical acceptor residues (R and/or R = CN, C02R) in the 6-position.53, 72 This substitution, however, again as in the hydrocarbon series,73 lowers the basicity to such an extent that the dinitrile (52) (Rj = R2 = H, R = R = CN), for example, is not appreciably protonated even in pure trifluoroacetic acid.52... 

The benzyl derivative (152) is deprotonated to the crystalline 1,2-dithiafulvene (153) by aqueous soda solution. The ease of formation and the stability of these 3-methylene derivatives are strongly influenced by the substituents.119... 

The attack of the acid (154) on the readily polarizable 1,2-dithiafulvene (155) corresponds to the extremely ready addition of electrophilic reagents to the simple and vinylogous heptafulvene derivatives, which are iso-n-electronic with 155. The opening of the dithiole rings in 156 and 158 under the pressure of the carbanionoid electron pair liberated by the proton abstraction and of the free electron pair on the sulfur, as well as the elimination of elementary sulfur and the intramolecular electrophilic attack of the mercaptide ion (157) on the 5-position to form 158, are simply the typical reactions of 1,2-dithioles that have already been discussed (Section II, B, 3). The reactivity of the 3-methyl group in 154 finds many parallels in the ease of condensation of the methyl-substituted pyridinium, pyrylium, thiopyrylium, and tropylium salts, and particularly... 

The synthesis, electrochemical and electronic absorption properties, crystal structure, and molecular orbital calculations of catechol-appended TTF derivative 67 (13TL4015) and a review into chalcogen-rich compounds as electron donors (B-13MI99) have been published. The synthesis, structure, and electronic properties ofthe bromophenyl-substituted dithiafulvenes 68-70, tetrathiafulvalene vinylogues (TTFVs) 71-73, and the unusual spiro-compound 74 produced from 70 have been reported... 

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