The double protonation of dihapto-coordinated benzene complexes enables dearomatization using aromatic nucleophiles

Abstract

Friedel-Crafts Arylation (the Scholl reaction) is the coupling of two aromatic rings with the aid of a strong Lewis or Brønsted acid. This historically significant C–C bond forming reaction normally leads to aromatic products, often as oligomeric mixtures, dictated by the large stabilization gained upon their rearomatization. The coordination of benzene by a tungsten complex disrupts the natural course of this reaction sequence, allowing for Friedel-Crafts Arylation without rearomatization or oligomerization. Subsequent addition of a nucleophile to the coupled intermediate leads to functionalized cyclohexenes. In this work, we show that by coordinating benzene to tungsten through two carbons (dihapto-coordinate), a rarely observed double protonation of the bound benzene is enabled, allowing its subsequent coupling to a second arene without the need of a precious metal or Lewis acid catalyst.