Controlled Interconversion of a Dinuclear Au Species Supported by a Redox-Active Bridging PNP Ligand Facilitates Ligand-to-Gold Electron Transfer.

Abstract

Redox non‐innocent ligands have recently emerged as interesting tools to obtain new reactivity with a wide variety of metals. However, gold has almost been neglected in this respect. Here, we report mechanistic investigations related to a rare example of ligand‐based redox chemistry in the coordination sphere of gold. The dinuclear metal‐centered mixed‐valent AuI–AuIII complex 1, supported by monoanionic diarylamido‐diphosphine ligand PNPPr and with three chlorido ligands overall, undergoes a complex series of reactions upon halide abstraction by silver salt or Lewis acids such as gallium trichloride. Formation of the ultimate AuI–AuI complex 2 requires the intermediacy of AuI–AuI dimers 5 and 7 as well as the unique AuIII–AuIII complex 6, both of which are interconverted in a feedback loop. Finally, unprecedented ortho‐selective C−H activation of the redox‐active PNP ligand results in the carbazolyldiphosphine derivative PN*PPr via ligand‐to‐metal two‐electron transfer. This work demonstrates that the redox‐chemistry of gold may be significantly expanded and modified when using a reactive ligand scaffold.