Abstract
Evidence is presented to show that the reaction of all M(S–S)2 compounds [M = Pt, Pd; (S–S)=S2CNR2(R = Me, Et), S2COR (R = Et, PhCH2), S2P(OEt)2, and S2PR2(R = Me, Et, Ph)] with tertiary phosphines occurs by stepwise cleavage of metal–sulphur bonds to generate four-co-ordinate compounds of formulae [M(S–S)2PR′3] and [M(S–S)(PR′3)2](S–S) with unidentate/bidentate (III) and ionic/bidentate (IV) co-ordination respectively. All the ionic compounds readily revert to the [M(S–S)2PR′3] complexes in the presence of non-polar solvents via nucleophilic attack by (S–S) on the metal. In addition, for (S–S)=S2COR, S2P(OEt)2, nucleophilic attack can also occur on a co-ordinated alkoxy group to give the novel compounds [(R′3P)2MS2CO](I) and [(R′3P)2MS2P(O)OEt](II) respectively. For [M(S–S)(PR′3)2](S–S) compounds containing S2CNR2, the presence of excess PR′3 catalyses the reaction between dithiocarbamate ion and dichloromethane, giving CH2(S2CNR2)2 and [M(S2CNR2)(PR′3)2]Cl, H2O. These conclusions are based on extensive physico-chemical studies and, in particular, the use of variable temperature 1H n.m.r. spectroscopy.

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