8 - Diaryl Iodonium Salts

Abstract

This chapter discusses diaryl iodonium salts, and some related heteroaromatic and heterocyclic analogues. Arylation is the dominating reaction of diaryl iodonium salts. From the application point of view, they are useful in photopolymerizations and for chemical amplification in imaging systems. A large number of methods are available for the preparation of diaryl iodonium salts. These salts are usually obtained directly from arenes or organometallics and an inorganic compound of iodine (III) or (V). Once formed, iodonium salts can exchange their anion with almost any other anion; exceptions are hydrosulfide, sulfide and cyanide. For large-scale preparations one of the early methods is always useful and can be applied to arenes of various kinds, including those bearing electron-withdrawing substituents. Most known iodonium salts of this category have one phenyl and one aryl group. Various hypervalent iodine precursors can be used as effective electrophiles, notably the combination of (diacetoxyiodo)benzene with triflic acid. The reagent is formed in situ and is suitable for a range of activated to weakly deactivated arenes. Most iodonium salts are exceptionally stable and unreactive towards electrophiles and weak nucleophiles.