Computational and experimental evidence for Sb(<scp>v</scp>) metal mediated C–H activation and oxidative functionalization of arenes

Inorganic Sb^V complexes are one of the most well-known Lewis acids that typically indirectly activate nonpolar hydrocarbon bonds by acting as Brønsted superacids. Here we have used a combination of quantum-chemical calculations and experiments to demonstrate that inorganic Sb^V complexes can directly activate aromatic sp² C-H bonds and induce oxidative functionalization to form aryl esters. C-H activation was first demonstrated by reaction of Sb^V(TFA)₅ (TFA = trifluoroacetate) with toluene at moderate temperatures that resulted in Sb^V-C bond intermediates (TFA)₄Sb^V(<i>para</i>-tolyl) and (TFA)₃Sb^V(<i>para</i>-tolyl)₂. Calculations predicted and then experiments confirmed that at a higher temperature reductive functionalization occurs to generate oxidized aryl ester products. Theory and experiment indicate that due to a Curtin-Hammet type equilibrium the initial <i>para</i> C-H activation regioselectivity changes to mainly <i>ortho</i> and <i>meta</i> selectivity for reductive oxy-functionalization.