The Evolution of [{Ph2P(CH2)nPPh2}Pt(μ‐S)2Pt{Ph2P(CH2)nPPh2}] (n=2, 3) Metalloligands in Protic Acids: A Cascade of Sequential Reactions

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Abstract
Given the nucleophilicity of the {Pt2S2} ring, the evolution of [Pt2(μ‐S)2(P∩P)2] (P∩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 {Pt2S2} core to be established. The titration of [Pt2(μ‐S)2(P∩P)2] with HCl or HClO4 was monitored mainly by 31P{1H} NMR and mass techniques. Characterization of all the species involved was completed with the determination of the crystal structure of [Pt(SH)2(P∩P)], for dppe and dppp, and [Pt3(μ3‐S)2(dppp)3](PF6)2. The first protonation step of the {Pt2S2} core leads to the stable [Pt2(μ‐S)(μ‐SH)(P∩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 [Pt2(μ‐S)(μ‐SH)(P∩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 ClO4− determines the nature of the final products, [PtCl2(P∩P)], [Pt3(μ3‐S)2(P∩P)3]Cl2 or [Pt3(μ3‐S)2(P∩P)3](ClO4)2. DFT calculations have corroborated the thermodynamic feasibility of the reactions proposed on the basis of experimental data.

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