Thiolates monodentate

Thiolates (RS ) represent an extensive family of ligands, and include chelating forms. Thiolates are known to act as monodentate donors, but often act in a bridging role. There is a clear biological interest, through participation of thiolates (cysteine residues) as donors in many metalloproteins both as terminal S donors and bridging ligands in, for example, Fe S clusters. 

Regular pyrimidines are less effective ligands for Ni11 ions. They may use, inter alia, their C=0 donor to yield monodentate coordination.1835 Insertion of a sulfur atom into a pyrimidine moiety increases considerably its binding ability.1836 Thiolation of uridine at C(2) or C(4) results in formation of a quite effective S,N3 four-membered chelate in the complexes with Ni11. Thiolation of purine at C(6) increases the stability constant by 3.5 orders of magnitude. 

Monodentate or multidentate thiols as the ligand coordinate are anionic donors in form of thiolates. The metal core of their complexes is normally [M =0] 3 +. The charge requirements of this core are easily met by the ligands. In the case of pure thiolato coordination, anionic complexes result. In a few cases, neutral binuclear oxo complexes and oxo-free species also occur. 

A number of neutral mixed-ligand oxorhenium(V) complexes containing tridentate [SC2H4YC2Lt4S] (Y = S,0) (95) and monodentate, monoanionic thiolate ligands have been prepared from [ReOCU] and a mixture of the ligands (Scheme The intermediate... 

For complexes of type Pt(SR)2L2 with monodentate thiolate and ligands L the isolated product usually has trans stereochemistry. This is not necessarily the kinetic product, however, since exposure of the cis complexes to oxygen causes rearrangement to the trans isomer and other products.1708... 

In general, these reactions are better characterised with chelated thiolate ligands rather than with monodentate thiolates, although many reactions giving rise to monodentate coordinate thioethers are known. A typical example is shown in Fig. 5-77, in which an iron(n) thiolate is converted to a thioether complex. 

A great number of studies have addressed the photophysical properties of related Zn(diimine)(SR)2 complexes. Crosby and co-workers (136, 137) investigated many mixed-ligand complexes of Zn(II) and Cd(II) containing diimine ligands and monodentate aromatic thiolate ligands. They note that the rotational... 

More recently three other mononuclear [Fe(SR)4]- complexes containing monodentate thiolate have been structurally defined. In these SR = SPh-,219 SEt-219 and 2,3,5,6-tetramethylben-zenethiolate.220 Sterically hindered thiolate ligands appear to stabilize the [Fe(SR)4] coordination unit and thus provide a means for the preparation by ligand exchange of the previously elusive (non-hindered) monodentate tetrathiolato iron(III) complexes. 

Co6S(SEt)4(CO)M] respectively (Table 80). In the absence of solvent [Co2(CO)8] and EtSH form [Co5(SEt)5(CO)10]"7 for which a crystal structure is also available.998 In these cobalt-carbonyl-thiolate systems the S atoms doubly or triply bridge metal centres and there appears to be no examples where RS" functions as a monodentate ligand. 

Table 82 Preparations Monodentate and Bidentate Thiolate Chelates of Cobalt(IU) (Not Containing Mixed Ligand...

It has been shown that reaction of Mn30(02CPh)6(py)2(H20) with [NEt3H]2(biphenoxide) results in the formation of [Mn(III)(biphen)2-(biphenH)]2- (biphen = 2,2 -biphenoxide) (Fig. 5) (143). The complex is a rare example of five-coordinate Mn(III) without softer ligands such as thiolate or chloride. The monodentate biphen-Mn bond represents the first stable example of the Mn phenoxide couple. The monomer displays several intense absorption bands (Table VI). In DMSO (where the compound may be six coordinate), a band at 430 nm, very similar to that of the enzyme, is assigned to a phenoxide - Mn(III) charge transfer band. 

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