Mechanistic Investigation into RhIII-Catalyzed Intramolecular Redox-Neutral Annulation of Aryl Hydrazines with a Tethered Alkyne

A mechanistic study of the Cp*Rh-III-catalyzed (Cp*=(5)-pentamethylcyclopentadienyl) intramolecular redox-neutral annulation of tethered alkynes was carried out by density functional calculations using the M06 method. Our results show that the reductive elimination step of the catalytic cycle is rate determining, and the overall energy barrier of the entire process is 31.4kcalmol(-1) (L-IIL-TS8-9). This is in agreement with experimental results that reported the C-H bond cleavage not to be the rate-determining step. According to our calculations, the feasible mechanism for the (RhRhRhIII)-Rh-III-Rh-V process involves an acylamino migration and subsequent reductive elimination process, which is different from the pathway previously proposed by Li's group. The present calculations elucidate the experimental observations on the molecular level.