Synthesis and Characterization of Stable Gold(III) PNP Pincer Complexes

The first mononuclear Au^III PNP pincer complexes [PNP = bis(2-diisopropylphosphinophenyl)amide] are reported. The chloro complex [(PNP)Au(Cl)][OAc^F] (OAc^F = OCOCF₃) was synthesized by microwave irradiation of a tetrachloroaurate salt and the neutral PNHP ligand. Dehalogenation with AgOAc^F afforded the trifluoroacetate-bound complex [(PNP)Au(OAc^F)][OAc^F]. Both complexes were characterized by NMR spectroscopy and X-ray crystallography. Electronic absorption spectroscopy and TD-DFT studies assigned the electronic transition that imbues the complexes with a deep royal blue color. The Au^III trifluoroacetate complex is surprisingly stable, and no alkene insertion was observed under ethylene (C₂H₄), even under high pressures and at high temperatures. DFT calculations suggest that the lack of reactivity is due to the high energy of the putative dicationic C₂H₄-bound intermediate invoked in a formal insertion reaction.