Chelation sulfur types

A number of metal ions in biological situations are bound essentially by sulfur donor groups (50), and thus chelates of type l,3-bis-(o-methylthiophenylthio)propane (S4) (31) have added interest. Apparently this ligand does not form monomeric complexes the only species isolated thus far are the dimeric [Pd2(s4)X4] (X = Cl, Br, I) and [Pt2(s4)X4] (X = Cl, I), and the trimeric Rhg(s4)2Cl9. 

Sulfur-bound L-Met, as opposed to S,N-chelated L-Met, is more reactive as a ligand on Pt(II) and can be slowly replaced by N7 of G (95, 96). Transfer of Pt onto DNA via Met-containing peptides or proteins may therefore be possible. Monofunctional adducts of the type [Pt(en)(G)(L-Met-S)] appear to be very stable (97) and so methionine may play a role in trapping these adducts. Also, the high trans influence of S as a Pt(II) ligand can lead to the facile labilization of trans-am(m)ine ligands and this allows cisplatin to react with GMP faster in the presence of L-Met then in its absence (98), which introduces another route to DNA platination. 

Additional types of k C-k E chelating ylide complexes merit mentioning here, in addition to the species already presented, and some of them are shown in Scheme 24. The first is formed by ylides containing a pyridine functionality as substituent of the ylidic carbon. This type of ligand has allowed the S3mthesis of many loose clusters (82) of Cu, Ag, and Au which show weak metal( / °)-metal( / °) interactions. These facts have prompted the definition of a new phenomenon numismophilicity) to account for these weak interactions, uniquely shared by the three coinage metals [164]. Nitrogen and sulfur keto-stabilized ylides have been reacted with Pt and... 

---