Homobimetallic rhodium catalyst

Scheme 9.34 Rhodium-catalyzed directarylation reaction of benzene (87) with the homobimetallic rhodium catalyst 108.

A homobimetallic rhodium catalyst derived from a P,N-ligand was found to allow for intermolecular direct arylations of unfunctionalized arenes [24]. Interestingly, aryl iodides, bromides-and even chlorides-could be employed as electrophiles, and a variety of valuable functional groups was tolerated by the catalytic system (Scheme 9.12). The C—H bond functionalization of toluene yielded ortho-, meta- and para-substituted regioisomers in a ratio of 71 19 10. Based on this observation and a Hammett correlation, a mechanism proceeding through radical intermediates was suggested. 

NHC ligands have been used to bridge different metals resulting in homo-bimetallic systems. Examples exist for palladium(II), rhodium(I), as well as chromium(O). " Homobimetallic ruthenium(II) systems have been shown to be superior catalysts in cyclopropanation reactions compared to their monometallic... 

---