Stability of Ag^III towards Halides in Organosilver(III) Complexes

The involvement of silver in two-electron Ag^I /Ag^III processes is currently emerging. However, the range of stability of the required and uncommon Ag^III species is virtually unknown. Here, the stability of Ag^III towards the whole set of halide ligands in the organosilver(III) complex frame [(CF₃ )₃ AgX]^- (X=F, Cl, Br, I, At) is theoretically analyzed. The results obtained depend on a single factor: the nature of X. Even the softest and least electronegative halides (I and At) are found to form reasonably stable Ag^III -X bonds. Our estimates were confirmed by experiment. The whole series of nonradiative halide complexes [PPh₄ ][(CF₃ )₃ AgX] (X=F, Cl, Br, I) has been experimentally prepared and all its constituents have been isolated in pure form. The pseudohalides [PPh₄ ][(CF₃ )₃ AgCN] and [PPh₄ ][(CF₃ )₃ Ag(N₃ )] have also been isolated, the latter being the first silver(III) azido complex. Except for the iodo compound, all the crystal and molecular structures have been established by single-crystal X-ray diffraction methods. The decomposition paths of the [(CF₃ )₃ AgX]^- entities at the unimolecular level have been examined in the gas phase by multistage mass spectrometry (MSⁿ ). The experimental detection of the two series of mixed complexes [CF₃ AgX]^- and [FAgX]^- arising from the corresponding parent species [(CF₃ )₃ AgX]^- demonstrate that the Ag-X bond is particularly robust. Our experimental observations are rationalized with the aid of theoretical methods. Smooth variation with the electronegativity of X is also observed in the thermolyses of bulk samples. The thermal stability in the solid state gradually decreases from X=F (145 °C, dec.) to X=I (78 °C, dec.) The experimentally established compatibility of Ag^III with the heaviest halides is of particular relevance to silver-mediated or silver-catalyzed processes.