Structural and photochemical properties of organosilver reactive intermediates MeAg2(+) and PhAg2(+)

Although there is growing interest in silver promoted carbon-carbon bond formation, a key challenge in developing robust and reliable organosilver reagents is that thermal and photochemical decomposition reactions can compete with the desired coupling reaction. These undesirable reactions have been poorly understood due to complications arising from factors such as solvent effects and aggregation. Here the unimolecular decomposition reactions of organosilver cations, RAg(2)(+), where R = methyl (Me) and phenyl (Ph), are examined in the gas phase using a combination of mass spectrometry based experiments and theoretical calculations to explore differences between thermal and photochemical decompositions. Under collision-induced dissociation conditions, which mimic thermal decomposition, both PhAg(2)(+) and MeAg(2)(+) fragment via formation of Ag(+). The new ionic products, RAg(+?) and Ag(2)(+?), which arise via bond homolysis, are observed when RAg(2)(+) is subject to photolysis using a UV-vis tunable laser OPO. Furthermore, comparisons between the theoretical and experimental UV-vis spectra allow us to unambiguously determine the most stable structures of PhAg(2)(+) and MeAg(2)(+) and to identify the central role of the silver part in the optical absorption of these species. The new photoproducts result from fragmentation in electronic excited states. In particular, potential energy surface calculations together with the fragment charges highlight the role of triplet states in these new fragmentation schemes.