1.4- Dithiins metallation

Reactions of cyclopentadienyl- and (pentmethylcyclopentadienyl)iron dicarbonyl 2-alkynyl complexes as well as cyclopentadienylmolybdenum tricarbonyl 2-alkynyl complexes with 4,5-diphenyl-3,6-dihydro-l,2-dithiin 1-oxide 111 were shown to yield transition metal-substituted five-membered ring thiosulfinate esters 112 in moderate to excellent yields (Scheme 27) <19910M2936, 1989JA8268>. These reactions are formal [3-1-2] cycloadditions. When... 

Dithiin, 1,4-benzodioxin, and its 2-substituted derivatives can be readly deprotonated and trapped with electrophiles although the reaction is more problematic with 1,4-dioxin. Oxanthrene and phenoxathiin are cleaved with lithium <1996CHEC-II(6)447>. A more recent example deals with the metallation at C-3 of the 1,4-benzodioxane 60 bearing a carboxylic acid function at C-2, with lithium diisopropylamide (EDA) and subsequent quench with iodomethane. The corresponding 3-methylated benzodioxane 61 was isolated in 70% yield (Equation 6) <2000EJM663>. 

Dithiin is readily metallated at the 2-position by n-butyllithium at — 110°C, and (448) can be trapped at this temperature. At — 60°C ring opening occurs to give (449). 

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. 

Dithiin derivatives (dithiabenzenes) have long been known to react with metal carbonyls to give dithiolenes (285). A recent illustration is provided by the finding that treatment CpCo(CO)2 with 2-nitro-3,5-diphenyl-l,4-dithiin affords CpCoS2C2(Ph)H (286). 

A close structural relationship with I IF derivatives, especially BEDT-TTF, is exhibited by dddt metal complexes [dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate (63)]. The most interesting feature of this dithiolene ligand is the ability of its metal complexes to form not only anionic salts like dmit, but also cationic salts like TTF derivatives [89], to afford non-stoichiometric IR salts of type [M(dddt)2]mX . Thus the cyclic voltam-mogram of [Bu4N][Ni(dddt)2], after its initial oxidation, exhibits the reduction of neutral [Ni(ddt)2]° to anion [Ni(ddt)2]" at 0 V, and its further reduction to the dianion [Ni(dddt)2]2 , as well as the oxidation of [Ni(dddt)2]° to the cation [Ni(dddt)2] + at 0.8 V (MeCN versus Ag/Ag/Cl). The feasible synthesis of conducting donor-acceptor complexes involving dddt metal derivatives as donors and dmit metal derivatives as acceptors has also been demonstrated [90]. 

Dimercapto-l,3-dithiole-2-thione (dmit, 46) and 4,5-dihydro-l,4-dithiin-2,3-dithiolate (dddt, 47) ligands can be reacted with transition metal ions to give M(dmit)2 and M(dddt)2 complexes (M = Pt, Pd, Ni, and Au) [91]. The M(dmit)2 and M(dddt)2 anions, like BEDT-TTF, have numerous peripheral sulfur atoms and are planar. Additionally, they have variable redox potentials that can be adjusted through the metal that is selected. 

The expansion of the ir-conjugating system with outer heterorings, the idea presented by the ET molecule, can be applied to 1,2-dithiolene metal complexes with the donor character. For example, the M(dddt)2 (dddt=5,6-dihydro-l,4-dithiin-2,3-dithiol M = Ni, Pd, Pt, Au) molecule, where the central C = C double bond in ET is replaced by the transition metal, exhibits various molecular arrangements, some of which are similar to those found in the ET salts [29]. In the frontier molecular orbital of the 1,2-dithiolene complexes, the 3p orbitals of S atoms in the ligand show a significant contribution. In this sense, the molecular design for the 1,2-dithiolene complexes can be discussed in common with that for the organic ir molecules. 

In contrast to anionic [M(dmit)2] acceptor molecules, the metal complexes with dddt ligands, [M(dddt)2] (dddt = 5,6-dihydro-l,4-dithiin-... 

Compared to l,2-bis(methylthio)ethene, the structural and electronic conditions for metallation of 1,4-dithiin are even more favourable. The additional double bond is likely to exert an electron-withdrawing influence, while the greater rigidity... 

Diels—Alder Reaction and the Formation of Adducts with Olefins. The d -metal bisdithienes react with alkynes to form 1,4-dithiins (24) according to Equation 7 (17) ... 

Syn- and A-bis-benzothienyl-l,4-diselenins 193 and 194 have been prepared by metallation sequences (Equations 50, 51). The crystal structures of 193 and 194 were determined and compared with the corresponding dithiins <2006CL422>. These fused diselenins exhibit unusual redox properties, being less stable in the oxidized form than the corresponding dithiins. 

Dibenzylthiobutadienes 59 undergo reductive debenzylation under the action of sodium metal in liquid ammonia at — 70°C with the formation of sodium dithiolate (60) which is instantly oxidized either with air oxygen or with special oxidants (iodine, iron chloride) to 1,2-dithiines 55. l,4-Di(/-butylthio)buta-1,3-dienes (61) afford 1,2-dithiins 55 by treatment with (o-nitrophenyl)sulfenylchloride via disulfide 62. 1,2-Dithiins 55 can be transformed to the corresponding thiophenes 63 [see also (92MI1)]. The formation of 63 is also observed upon the fragmentation of compounds 55 in the mass spectra (principal peak) (96T12677). 

K. Kudoh, T. Okamoto and S. Yamaguchi, Reactions of fused polycyclic 1,2-dithiins with transition metals synthesis of heteroacenes via desulfurization, Organometallics, 25, 2374-2377 (2006). 

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