Selective Arene Cleavage by Direct Insertion of Iridium into the Aromatic Ring

Abstract

We report an unprecedented selective cleavage of aromatic C-C bonds through the insertion of well-defined iridium complexes into the aromatic ring of simple alkylarenes. The insertion occurs at 50-100 °C without the activation of weaker C-H and C-C bonds and gives unique metallacycles in high yields. Key to the success of this approach is metal-induced deformation of the arene ring, which creates temporary ring strain and promotes direct and selective insertion of the metal into the otherwise inert arene ring C-C bonds.

Transition‐Metal‐Mediated Cleavage of C−C Bonds in Aromatic Rings

“…A different approach for activation of aromatic C−C bonds was proposed by our group . To facilitate metal insertion into aromatic ring C−C bonds, we used simple Cp*Ir complexes 4 with η 4 ‐coordinated arene rings (Scheme ).…”

“…Ad ifferent approach for activation of aromatic CÀCb onds was proposed by our group. [21] To facilitatem etal insertion into aromatic ring CÀCb onds, we used simple Cp*Ir complexes 4 with h 4 -coordinated arene rings (Scheme 5). In these complexes the aromatic ring is bondedt ot he metal center through four carbon atoms and the remaining two carbon atoms make up an uncoordinated CÀCd ouble bond.…”

Selective cleavage of unactivated arene ring C–C bonds by iridium: key roles of benzylic C–H activation and metal–metal cooperativity

“…9,10 As a result, insertion of metal complexes into aromatic C-H bonds is overwhelmingly more common that insertion into aromatic C-C bonds. Of the seven examples of arene ring scission by a well-defined metal complexes reported to date, 11,12 only cleavage of C 6 (CF 3 ) 6 by a Pt complex, 13 and benzene and biphenylene by Al complexes 14,15 proceed selectively. In all other cases, [16][17][18][19] including reactions of Al complexes with alkylarenes, 19 C-H scission competes with or even dominates the reaction.…”

“…This C-C activation yields diiridium metallacycles with excellent yields and high regioselectivity without observable C-H activation products. 11,12 Consequently, these Cp*Ir complexes provide the best starting point found so far both for developing practical strategies of arene functionalisations and for understanding the mechanism of C-C vs. C-H selectivity and the role of the substituents in enabling selective arene cleavage. Here we describe the first mechanism of cleavage of arene ring C-C bonds in unactivated arenes of industrial importance that is consistent with both experimental (kinetic, isotope labelling, intermediate interception) and quantum-chemical data.…”

“…We previously observed that C-C bond activation in all Cp*Ir( 4methylarene) complexes reported to date has a similar kinetics, which suggests a common mechanism. 11,12 Among all these complexes, as a starting point for our experimental studies we chose Cp*Ir( 4 -mesitylene) as a model substrate because this complex and the metallacycle product, 2, each exists as a single isomer (Fig. 1C).…”