Investigation of Gold a-Oxo Carbene/Carbenoid Complexes as Key Intermediates in Gold(I) Catalysis

Cationic gold(I) complexes have recently contributed to significant developments in homogenous catalysis. Such complexes have been praised as highly effective catalysts for the functionalization of C-C multiple bonds, leading to research on cationic gold-catalysts developing at an aggressive pace. Despite the progress being made surrounding gold(I)-catalysis, there are still many gaps in our fundamental understanding of the key intermediate complexes and their reactivity in these transformations, exemplified by the often evoked gold alpha-oxo carbene species. While there are existing computational studies suggesting the instability of gold alpha-oxo carbene species, there lacks any experimental evidence to support the stability and reactivity of alternate key intermediate species, such as gold alpha-oxo carbenoid species and gold N-alkenoxypyridinium/sulfonium complexes. Herein, we address the issues surrounding the formation of gold alpha-oxo carbene species in reported literature. We report the synthesis and reactivity of gold pyridinium alpha-oxo carbenoid complexes, gold sulfonium alpha-oxo carbenoid complexes, and gold alpha,alpha-dioxo carbenoid complexes. We then report the direct observation of a gold N-alkenoxysulfonium complex in a gold-catalyzed alkynyl sulfoxide rearrangement reaction and the synthesis of a series of gold-oxide compounds. Together, this research addresses the gaps in knowledge surrounding key intermediate species in gold(I)-catalyzed transformations.