Thioethers multidentate

Multidentate thioethers are readily introduced into the coordination sphere of low-valent cobalt. As an example, the tridentate thioethers 1,3,5-trithiacyclohexane and tris(methylthio)methane both replace three facially arranged carbonyl ligands in Co3(CO)9(/i-CPh), leaving the cluster otherwise intact.169... 

Table 93 Structures Multidentate Thioether-CobaJt(Ill) Complexes...

Thioether ligand complexes are not very common, however, studies since the mid 1990s have dramatically increased the number of structurally characterized examples. Almost all of these compounds are with chelate or macrocyclic ligands that will stabilize thioether coordination. Mixed donor multidentate ligands containing thioether donors will be discussed in Section 6.8.11. 

Multidentate and macrocyclic ligands with thioether functions in combination with N- and/or O-donor groups are of interest in the development of new series of selective metal extractants e.g. for Ag(I).167... 

Dockal etal. [57] used slow-scan CV to determine the 21 values for 17 Cu(II/I) complexes in 80% methanol —20% water (w/w) - including nine complexes with macrocyclic terdentate, quadridentate, quinquedentate, and sexaden-tate thioethers and eight complexes with acyclic quadridentate ligands containing thioether sulfur and/or amine nitrogen donor atoms. (In naming the denticity of multidentate ligands, Dwyer, Lions, and coworkers have pointed out that dentate is a Latin root and proper nomenclature requires that Latin prefixes be used. 

There is a small literature on multidentate O—S ligands possessing thioether sulfur atoms and carboxylic acid or hydroxy groups. Table 42 lists some of these compounds, together with their proposed stereochemistries and structures. In all compounds listed, binding of both all the sulfur atoms and all the carboxylic acid or hydroxy groups is proposed. 

Thioether complexes are mostly of the bidentate (301) or multidentate (302) type. Monodentate systems (303) are rare but are known (equation 167a),1078 and in such cases they provide useful starting materials since the thioether ligand is easily displaced. 

The many synthetic methods available for preparing NHCs have allowed for their ready incorporation into an increasingly diverse set of multidentate ligands. The topic of chelating ligands containing NHCs has been covered in several reviews.Heteroleptic variations have included phosphines, amines, imines, pyridines, oxazolines, amides, alkoxides, aryloxides, thioethers, and other donors. 

Sharrad CA, LUthi SR, Gahan LR (2003) Embracing ligands. A synthetic strategy towards new nitrogen-thioether multidentate ligands and characterization of the cobalt(lll) complexes. Dalton Trans 3693-3703... 

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