An Anionic Rhodium η⁴-Quinonoid Complex as a Multifunctional Catalyst for the Arylation of Aldehydes with Arylboronic Acids

The π-bonded rhodium quinonoid complex, K⁺[(1,4-benzoquinone)Rh(COD)]^-, functions as a good catalyst for the coupling of arylboronic acid and aldehydes to afford diaryl alcohols. The catalysis is heterobimetallic in that both the transition metal and concomitant alkali metal counterion play an integral part in the reaction. In addition, the anionic quinonoid catalyst itself plays a bifunctional role by acting as a ligand to the boronic acid and as a Lewis acid receptor site for the transferring aryl group.