Carbopalladation carbon-palladium single bonds

C.i.a. Four-Centered Processes. The carbopalladation of a C,C multiple bond with a carbon-palladium single bonds is the key step in the catalytic cycle of the standard Heck reaction, the intermolecular version of which has been used extensively since its discovery for the functionalization and derivatization of aryl and alkenyl halides, as well as alkenyl triflates or the more reactive nonafiates, which are readily available from the corresponding ketones (Scheme 2) (Sect. IV.2.1.2). 

Palladium-catalyzed vinylations of aryl halides are generally referred to as the Heck reaction (for reviews on the Heck reaction see [34-40]), a versatile process that can be performed inter- and intramolecularly [41]. In the Heck reaction the carbon-carbon single bond forming step is an insertion of an al-kene into the aryl-Pd bond, i.e., a carbopalladation, giving rise to an alkyl-Pd species. If this insertion is terminated by /1-hydride elimination the expected vinylation product is the outcome of the classical Heck reaction. Likewise, reversible insertion of a highly strained olefin where the /1-hydride elimination is suppressed leads to an entry to multiple Pd-catalyzed bond forming processes. 

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