Addition of Electrophilic Alkynes to Metal Sulfides

Metal per- and polysulfido complexes react with electrophilic alkynes to give dithiolenes. The readily available diester DM AD is most commonly employed 

The prototype reaction of DMAD with sulfur-rich metal complexes involves treatment of Cp2TiS5 with DMAD to give Cp2TiS2C2(C02Me)2 (Eq. 19) (188). 

DMAD is a highly reactive electrophile, so caution should be exercised in using this reagent. Illustrative of the complications that one can encounter, the reaction of Mo(S2)(S2CNEt2)3 with DMAD gives melded dithiolene complexes wherein the Et2NC fragment has inserted into the dithiolene M—S bond (230). 

Subsequent to the development of the titanocene dithiolenes, related results were obtained starting with ZnS,(tmeda), where tmeda = tetrameth-ylethylenediamine and ZnS4(pmdta) (189), where pmdta = pentamethyldieth-ylenetriamine (ligand). These species react with DMAD and HC2C02Me to give dithiolene complexes, and the dithiolene can also be readily removed from the zinc center. The zinc complexes are more potent dithiolene-transfer agents than the titanocene complexes. The pentacoordinate complex ZnS4(pmdta) reacts more rapidly with alkynes than the tmeda derivative (Fig. 17). 

The reaction of phenylethynylquinoxaline and [Mo(S)(S4)2]2 gives Mo-[S2C2(Ph)(CgH5N2)]3 2 (227), which probably exists as a mixture of rapidly 

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