1,1-Dithiolato metal complexes ligands

The literature concerning the chemistry of transition-metal complexes containing 1,1-dithiolato ligands was extensively reviewed, up to 1968, by Coucouvanis (1). We attempt here to update that excellent account. 

Monodentate (monometallic monoconnective) phosphor-1,1-dithiolato ligands are rare. Bidentate (monometallic biconnective) form chelate rings and three sub-types can be distinguished according to the degree of asymmetry (Scheme 2). The most asymmetric type (anisobidentate) occurs when a covalent bond is associated with a secondary bond this takes place mostly in main-group metal complexes. The second type is rare and is the result of the association between a covalent and a dative coordinate bond. The symmetric bidentate bonding (isobidentate) is found mainly in transition metal complexes. 

Abstract Metal complexes including the dmit2- (1,3-dithio-2-thione-4,5-dithiolato) ligand are the only class of metal bis-dithiolenes to give rise to superconductive molecular materials. This chapter first focuses on the description of these superconductive phases. Further sections describe the association of M(dmit)2 moieties with three types of magnetic molecules, i.e., metalloceniums, radical cations, and spin crossover complexes. 

A number of dithiolato-metal-dye complexes were synthesized117 by adding thionine (TH), tolusafranine (SAF) or methylene blue (MB) to a mixture of a metal salt and Na2(mnt) or H2(tdt). The composition of the products was determined from elemental analyses and valence state considerations. Peculiar stoichiometries were found, e.g. Mn2(mnt)5(SAF)6(OH)2 11H20, necessitating the assumption that equally unusual structures existed. Nonetheless, the molar absorption coefficients of the maximum absorption were larger for the complexes than the free dyes. In hexa-methylphosphoramide, the metal dithiolene accelerated the rate of photochemical reduction versus the free ligand with TH but retarded the rate for the SAF and MB complexes. 

Despite the ambiguity regarding the assignment of formal oxidation states to metal and ligand in many dithiolate complexes, the structure and properties of the benzyltriphenylphosphonium salt of tris(l,l-dicarboethoxyethylene-2,2-dithiolato)ferrate [BzPh3P]2[Fe(DED)3] (DED = structure 139) are considered486 to be best described in terms of an Fe,v complex. The structure is close in important details to that of the dithiocarbamate complex described above.485... 

Relatively few complexes of the early transition metals with 1,1-dithiolato ligands have been prepared and characterized. This is consistent with their classification as "hard or "class a acceptors. Thus,... 

In complexes of the dithiolene type ligands the oxidation number of the metal cannot unambiguously be determined, due to the uncertainty of the charge on the ligand. R2C2S2 can be considered either as a dinegative dithiolato anion or as a neutral dithio-keto ligand. 

---