Abstract
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 sp(2) 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)(4)Sb(V)(para-tolyl) and (TFA)(3)Sb(V)(para-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 para C-H activation regioselectivity changes to mainly ortho and meta selectivity for reductive oxy-functionalization.