whereas low - valent late transition metal catalysis has become indispensible for chemical synthesis , homogeneous high - valent transition metal catalysis is underdeveloped , mainly due to the reactivity of high - valent transition metal complexes and the challenges associated with synthesizing them . in this manuscript , we report a mild carbon - carbon bond cleavage reaction by a au(i ) complex that generates a stable au(iii ) cationic complex . 
 complementary to the well - established soft and carbophilic au(i ) catalyst , this au(iii ) complex exhibits hard , oxophilic lewis acidity . 
 this is exemplified by catalytic activation of ,-unsaturated aldehydes towards selective conjugate additions as well as activation of an unsaturated aldehyde - allene for a [ 2 + 2 ] cycloaddition reaction . 
 the origin of the regioselectivity and catalytic activity was elucidated by x - ray crystallographic analysis of an isolated au(iii)-activated cinnamaldehyde intermediate . 
 the concepts revealed in this study provide a strategy for accessing high - valent transition metal catalysis from readily available precursors .