Mechanistic Insight into the Rh(III)-Catalyzed C-H Activation of 2-Acetyl-1-Arythydrazines in Water.

A mechanistic study of the Cp*RhIII-catalyzed C-H functionalization of 2-acetyl-1-arythydrazines with diazo compounds in water was carried out by using density functional theory calculations. The results reveal that the acetyl-bonded N-H deprotonation is prior to the phenyl C-H activation. The mechanisms from protonation by acetic acid disagree with the proposal by the Wang group. Different from the Rh(III)-catalyzed C-H activation reported by experimental literature, the rate-determining step of the whole catalytic cycle with an overall barrier of 31.7 kcal mol-1 (IV → TS12-P') is the protonation process of hydroxy O rather than the C-H bond cleavage step. The present theoretical study rationalizes the experimental observation at the molecular level.