Anionic derivatives of perfluorinated trimethylgold: synthesis and decomposition

Abstract

The study of fundamental processes involving organogold complexes is a topic of much current interest. In this context, the properties of trimethylgold, (CH3)3Au, and its derivatives have been widely studied as the most basic representatives of triorganogold compounds —with especial attention being focused on their decomposition mechanisms. Little is known, however, on the chemistry of the perfluorinated homologue (CF3)3Au, which is probably due to the lack of suitable experimental procedures to arrive at this kind of compounds. Given the sharply different properties of the CH3 and CF3 groups, we undertook a theoretical study of the perfluorinated (CF3)3Au fragment in order to establish its analogies and especially its differences with the well-known (CH3)3Au moiety. At the experimental level, convenient synthetic methods have been devised to prepare the series of anionic [PPh4][(CF3)3AuX] derivatives with all non-radioactive halide ligands: X = F, Cl, Br, I. Additionally, the cyano complex [PPh4][(CF3)3AuCN] was also synthesized. All these anionic compounds exhibit remarkable thermal stability -the latter decomposing at 351°C. The decomposition of these anionic compounds has been studied both in the gas phase and in the solid state. In the gas phase, where only unimolecular processes occur, the primary decomposition pathways given in the Scheme are operative. Aside from the organogold fluoride derivative [(CF3)3AuF]− for which CF2 extrusion is preferred, CF3–CF3 elimination is the most favored path in all cases. Interestingly, this high-energy decomposition pathway is completely absent in the condensed phase, where lower-energy intermolecular avenues are open. Transfer of CF3 groups between gold centers as well as trifluoromethylation of the phenyl rings in the cation are observed. [Scheme]: Primary intramolecular decomposition pathways observed by tandem mass spectrometry on the anionic species [(CF3)3AuX]− (X = F, Cl, Br, I, CN).