On the basis of these results we obtained and found in the
literature3,13 a plausible reaction mechanism that was proposed
and is shown in Scheme 2. First, Pd(OAc)2 reacted with
azobenzene by chelation-directed C−H bond activation to form
a five-membered cyclopalladated intermediate A,9,14 which has
been confirmed by previous research.7f Then the palladacycle A
reacted with the benzoyl radical,15 which was formed in situ
from the oxidation of toluene, and produced the dimeric
Pd(III)16 or reactive Pd(IV)17 species B. Finally, the
intermediate B underwent reductive elimination and provided
the acylazobenzene C. Meanwhile, the Pd(II) was regenerated
for the next catalytic cycle.