Lewis acid activation of Weiss’ Reagents ([PhI(Pyr)2]2+) with boranes and isolation of [PhI(4-DMAP)]2+

Abstract

Abstraction of a pyridine ligand from Weiss’ reagent ([PhI(Pyr)2]2+) using BF3-Et2O was found to activate Weiss’ reagent towards electrophilic aromatic substitution reactions. The activated species can be isolated when 4-DMAP is used as the pyridine ligand and was determined to be a [PhI(4-DMAP)]2+ in solution, and is associated with a triflate counterion in the solid state. The isolated cation was reactive in electrophilic aromatic substitution reactions towards mesitylene, xylene and toluene that Weiss’ reagent itself does not react with. If pyridine is used as the ligand the intermediate that results from abstraction cannot be isolated but is even more active, being observed to react with benzene.