The evolution of [[Ph2P(CH2)nPPh2]Pt(mu-S)2Pt[Ph2P(CH2)nPPh2]] (n=2, 3) metalloligands in protic acids: a cascade of sequential reactions

Given the nucleophilicity of the Pt(2)S(2)] ring, the evolution of Pt(2)(mu-S)(2)(P intersection P)(2)] (P intersection P=1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp)) metalloligands in the presence of the simplest electrophilic species, the proton, has been studied. Combined use of experimental and theoretical data has allowed the whole set of reactions ensuing the protonation of the Pt(2)S(2)] core to be established. The titration of Pt(2)(mu-S)(2)(P intersection P)(2)] with HCl or HClO(4) was monitored mainly by (31)P(1)H] NMR and mass techniques. Characterization of all the species involved was completed with the determination of the crystal structure of Pt(SH)(2)(P intersection P)], for dppe and dppp, and Pt(3)(mu(3)-S)(2)(dppp)(3)](PF(6))(2). The first protonation step of the Pt(2)S(2)] core leads to the stable Pt(2)(mu-S)(mu-SH)(P intersection P)(2)](+) complex, but the second step implies disintegration of the ring, thus giving rise to various mononuclear species. The subsequent evolution of some of these species allows regeneration of Pt(2)(mu-S)(mu-SH)(P intersection P)(2)](+), evidencing the cyclic nature of this process. Whereas the reaction pathway is essentially common for both phosphine ligands, dppe and dppp, the different coordinating ability of Cl(-) or ClO(4) (-) determines the nature of the final products, PtCl(2)(P intersection P)], Pt(3)(mu(3)-S)(2)(P intersection P)(3)]Cl(2) or Pt(3)(mu(3)-S)(2)(P intersection P)(3)](ClO(4))(2). DFT calculations have corroborated the thermodynamic feasibility of the reactions proposed on the basis of experimental data.