Conformational Switching through the One-Electron Reduction of an Acridinium-based, γ-Cationic Phosphine Gold Complex

Our efforts in the chemistry of gold complexes featuring ambiphilic phosphine-carbenium L/Z-type ligand have led us to consider the reduction of the carbenium moiety as a means to modulate the gold-carbenium interaction present in these complexes. Here, it was shown that the one-electron reduction of [(o-Ph2P(C6H4)Acr)AuCl](+) (Acr=9-N-methylacridinium) produces a neutral stable radical, the structure of which showed a marked increase in the Au-Acr distance. Related structural changes were observed for the phosphine oxide analogue [(o-Ph2P(O)(C6H4)Acr](+), the reduction of which interfered with the P=O -> carbenium interaction. These structural effects, driven by a reduction-induced change in the electronic and electrostatic characteristics of the compounds, showed that the charge and accepting properties of the carbenium unit can be modulated. These results highlight the redox-noninnocence of carbenium Z-type ligand, a feature that can be exploited to induce specific conformational changes.