Evidence for BINAP-Stabilized Gold(II) Species in a Catalytic Bromination Reaction of Terminal Alkynes.

Despite significant advances in gold chemistry, the EPR spectroscopic identification of a transient Au(II) species remains highly challenging. Herein, in the study of a bromination reaction of terminal alkynes enabled by a structurally rigid [Au(BINAP)(TFA)]2 complex as a precatalyst, a novel BINAP-stabilized gold(II) intermediate has been generated in situ and identified by EPR spectroscopy in the case of an oxidation reaction of a binuclear [Au(BINAP)(TFA)]2 with N-bromosuccinimide (NBS). Structurally rigid [Au(BINAP)(TFA)]2 complex is the essential factor to form Au(II) species with triplet spin state and subsequent further dissociation to mononuclear gold species.