Metal Tamao-Kumada-Corriu

Scheme 5.1 A general mechanism for metal-catalyzed Kumada-Corriu-Tamao coupling reactions.

The Zr-Co complex [(NjlCof PtjPNMesljZrfthf)] (20) has been found to catalyze the hydrosi-lylation of ketones. Since the direct interaction of the complex with benzophenone gave rise to a metal-bonded ketyl radic2il, a reaction mechanism involving such a radical species has been postulated by Thomas and coworkers [35]. The same complex was also found to be a precatalyst for Kumada-Corriu-Tamao coupling reactions [36]. 

The reaction of aryl electrophiles with organomagnesium compounds is known as Kumada or Kumada-Tamao-Corriu reaction. The most common leaving groups in the electrophile are halogen atoms and, among them, chlorine is the most wanted due to the good availability and the low price of aryl or heteroaryl chlorides. Unfortunately, the oxidative addition of a metal center to an aryl chloride is a difficult reaction and many efforts have been made to overcome existing limitations. 

Silicon, an element widely used in many facets of organic chemistry [7], was not effectively employed in cross-coupling reactions until 16 years after the first reported transition-metal-catalyzed coupling reactions by Corriu, Kumada, and Tamao [8], Most early developments in this field were achieved by the use of organoboron (1979) [9], organozinc (1977) [10], and organotin (1977) [11] coupling partners (Scheme 7.1). 

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