Remote C-H activation via through-space palladium and rhodium migrations.

The catalytic activation of a C-H bond is a fundamentally important organic transformation. There are now numerous reports of palladium-mediated C-H activation by the through-space interaction of a palladium center with a neighboring C-H bond. This type of C-H activation can lead to a net "palladium migration" from the carbon atom where the palladium is first introduced to a remote carbon atom where C-H activation occurs. This process provides a novel method to introduce a palladium moiety into a position where direct palladium introduction may not be straightforward. This process is accompanied by concurrent migration of a hydrogen atom in the direction opposite to that of the palladium migration. Analogous rhodium migrations have also been reported. In this account, different types of palladium and rhodium migrations are reviewed and the reaction mechanism is discussed.