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

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 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(para-tolyl) and (TFA)₃Sb^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.