Abstract

The traditional Ullman reaction is the homocoupling of aromatic halides mediated by copper at elevated temperatures. Ullman first reported this reaction in 1901. Although the coupling conditions first reported are still widely used, a host of modifications have been made to these reactions. Some of these modifications include the use of activated and alternative metals, often resulting in much lower coupling temperatures. Nickel and palladium are the most utilized source of alternative metals, Periodic reviews have been published. This chapter covers the literature on copper, nickel, and palladium mediated homocoupling reactions in biaryl synthesis from 1901 to 2000. The focus of this chapter is the scope and limitation of these processes, preparation of the activated metal, and mechanism of the homocoupling process