C–H Activation of π‑Arene Ruthenium Complexes

We present a C–H activation protocol for aromatic compounds that overcomes the current limitations of the need for a directing group or covalently bound activating groups, by exploiting the increase in C–H acidity of aromatic compounds on π-coordination to a Ru­(II) center. The increased acidity facilitates catalytic concerted metalation–deprotonation and subsequent arylation reactions. We present the development and optimization of the C–H activation protocol and show the applicability of the reaction to a range of aromatic substrates, including the simplest of substrates (benzene). Furthermore, we demonstrate the recyclability of the activating Ru­(II) fragment using photolysis and give a mechanistic study, which provides strong evidence that this reaction occurs via a silver-mediated C–H bond activation. This is the first time Ru complexes have been shown to allow C–H activation of arenes by a π-coordination mechanism.