Platinum, thiolate complexes

The aim of this chapter is to review the chemistry of chalcogenolates in the last 10 years. The more recent reviews in this field included chalcogenolates of the s-block elements,13,14 early transition metal thiolates,15 metal complexes with selenolate and tellurolate ligands,16 copper(I), lithium and magnesium thiolates,17 functionalized thiolate complexes,18 19 pentafluorobenzenethiolate platinum group compounds,20 tellurium derivatives,21 luminescent gold compounds,22 and complexes with lanthanide or actinide.23... 

Sulfur, thiolates and sulfide ligands form very stable complexes with platinum. Many complexes have platinum in the divalent state, but complexes with a Pt—S bond are formed with platinum in the zerovalent or tetravalent state. Several recent reviews have been written on various aspects of the platinum coordination chemistry of sulfur heteroatom ligands, and these are listed in Table 9. 

An alternative synthetic route to platinum(II) thiolates is by the oxidative addition of the S—S bond to platinum(O). When the sulfur atom has phenyl or electron-withdrawing substituents such as CF3, this reaction is a useful one to synthesize the thiolato platinum(II) complexes (equation 503).1703-1705 Simple alkyl disulfides such as Me2S2 and Et2S2 do not form stable dithiolato complexes of platinum(II) by S—S addition to Pt(PPh3)3, but if chelation can occur, chelate-assisted oxidative addition can induce S—S cleavage (equation 504).30 An unusual cyclic thiolato complex is obtained by the decarbonylative cleavage of a C—S bond (equation 505).1707... 

Platinum(lV) thiolate complexes are uncommon, primarily because the thiolate ligand, and thiols in general, are unstable to oxidizing conditions. The reaction between thiophenol and PtMe2L2 may proceed via platinum(IV) thiolates as intermediates, but only the platinum(II) derivatives have been isolated (equation 508).1711... 

Other means of improving sulfide yields in the reaction of halides with thiolates are (1) the use of thiols and platinum(II) complex catalysts287, (2) the generation of thiolate anions by electrochemical means288 and (3) the use of phase-transfer conditions237. The first method has been used for the synthesis of thioketals from geminal diiodides and the third has been used for the conversion of gem-dichlorocyclopropanes into cyclopropane thioketals, which are effectively masked cyclopropane moieties. 

A few final comments should be made on the insertions of substrates containing C-C multiple bonds into the bonds between a transition metal and an electronegative heteroatom. First, insertions of olefins into related thiolate and phosphide complexes are as rare as insertions into alkoxo and amido complexes. Reactions of acrylonitrile into the metal-phosphorus bonds of palladium- and platinum-phosphido complexes to give products from formal insertions have been observed, and one example is showm in Equation 9.90. However, these reactions are more likely to occur by direct attack of the phosphorus on the electrophilic carbon of acrylonitrile than by migratory insertion. Second, the insertions of alkynes into metal-oxygen or metal-nitrogen covalent bonds are rare, even though the C-C ir-bond in an alkyne is weaker than the ir-bond in an alkene. 

Weinstein JA, Zheligovskaya NN, Mel nikov MY et al (1998) Spectroscopic (UVAHS, resonance Raman) and spectroelectrochemical study of platinum(D) complexes with 2,2 bipyridine and aromatic thiolate ligands. J Chem Soc Dalton Trans 2459-2466... 

Platinum(O) complexes such as Pt(PPh3)4 also catalyze carbonylative thiolation of allenes, affording a,p- and p,y-unsaturated thioesters in good yields [116]. When 2-iodobenzenethiols are employed for the palladium-catalyzed carbonylation with... 

Platinum(II) thiolates can be decomposed in strong acid because of protonation at sulfur (equation 509). This reaction is similar to electrophilic alkylation at the coordinated thiolate, although in this case the thioether complex may be isolable (equation 510). Thiolato ligands are unreactive to nucleophiles, and only under the most forcing conditions does ligand replacement occur. 

The formation of complexes of l,2,3,4-thiatriazole-5-thiol has been well described in CHEC-II(1996) 1,2,3,4-thiatriazole-5-thiol can form complexes with various metals such as palladium, nickel, platinum, cobalt, zinc, etc. <1996CHEC-II(4)691>. These complexes can be prepared either by cycloaddition reactions of carbon disulfide with metal complexes of azide anion (Equation 20) or directly from the sodium salt of l,2,3,4-thiatriazole-5-thiol with metal salts. For instance, the palladium-thiatriazole complex 179 can be obtained as shown in Equation (20) or it may be formed from palladium(ll) nitrate, triphenylphosphine, and sodium thiatriazolate-5-thiolate. It should be noted that complexes of azide ion react with carbon disulfide much faster than sodium azide itself. 

From the studies reviewed above it has become evident that competion studies between thiols/thioethers and intact double-helical DNA are required, to find out whether or not the formation of the Pt-GG chelate is a driving force that can overcome the Pt-S interactions. Even then, one should realize that we are only dealing with a model, as in the cell other metals might also play a role in the disruption of Pt-S bonds. In this respect it should be mentioned that it was recently reported that addition of transition metals such as Zn11 or Cu11 can cleave even the Pt-S bond in thiolated terpyridine-platinum complexes at neutral pH [87],... 

The coordination chemistry of palladium and platinum with large aromatic thiolates has been restricted to some studies with PFTPH, although there is an extensive reported chemistry of oligomeric complexes with smaller thiols. Halide complexes of Pd and Pt were shown to react with Tl(PFTP) to give the presumably monomeric, square planar anionic M(II) complexes [M(PFTP)4] (83). 

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