Chemistry
The Chemistry of Diaryliodonium Salts as Electrophilic Arylating Agents
Quick fact
Diaryliodonium salts can transfer an aryl group to nucleophiles such as amines, alcohols, and even carbon nucleophiles without the need for a transition-metal catalyst, often at room temperature. They owe this remarkable reactivity to the excellent leaving group ability of the iodobenzene moiety.
Why this is interesting
You've probably seen reactions that need a metal catalyst and a precious ligand to put an aryl group onto a molecule. But what if you could do it with just a simple salt, no metal required?
Read the full explanation
Understanding The Chemistry of Diaryliodonium Salts as Electrophilic Arylating Agents
Imagine a molecule that carries a positive charge on an iodine atom that is also bonded to two aryl rings. This is a diaryliodonium salt, a type of hypervalent iodine compound. The positive charge makes the iodine very electron-poor, and the aryl rings are attached to it. A nucleophile, such as an amine, can attack one of the aryl carbons directly. The iodine then leaves with the other aryl group as a neutral molecule (iodobenzene). This is why chemists call them 'electrophilic arylating agents': they can donate an aryl group to a variety of partners. The key to their reactivity is the exceptional ability of the iodine moiety to act as a leaving group, which is due to the stability of the departing neutral iodobenzene and the high energy of the starting salt.
A deeper explanation
The mechanism begins with the nucleophile attacking the electron-deficient carbon of one of the aryl rings, forming a short-lived intermediate. This is favored because the iodine is so electronegative that it can accept the electron density, and the leaving group (iodobenzene) is extremely stable. The departing group takes the bonding electrons with it, and the other aryl group departs as a neutral molecule, leaving the new aryl–nucleophile bond formed. This process is called a ligand coupling reaction, and it occurs without the need for a metal catalyst. The driving force is the release of strain and the formation of a very weak bond, making the reaction thermodynamically favorable. Because the reaction proceeds through a direct attack on the aryl group, it can be used to arylate a wide range of nucleophiles—nitrogen, oxygen, sulfur, carbon—even in complex molecules, and it often shows high functional group tolerance.