text: The mechanism of carboboration depends highly on the substrate and reagents utilized in the reaction. Shown below are examples of two types of Pd-catalyzed alkene 1,2 carboborations, Heck-type and the Wacker-type. However, the Cu- and Ni-catalyzed reactions can proceed through similar mechanisms. These two mechanisms mainly differ in the oxidation state of the active catalyst and how the carbon group is delivered to the substrate: whether the C–C bond is formed via migratory insertion from the catalyst (inner sphere) or attack by an external nucleophile (outer sphere). Wacker-type carboborations, catalyzed by Pd, are much rarer than Heck-type. The first example of a Wacker-type 1,2 carboboration was reported by the Engle group in 2019.
  Despite the common trend of utilizing transition metals, transition metal-free processes have also been developed, such as utilizing boronic acids or light-mediated radical initiation. These reactions usually lead to the boron substituent being at the terminus or less substituted side of the substrate, but anti-carborborations have also been developed which produce reverse regioselectivity. Much work has also been done to render 1,2 carboboration enantioselective using various ligands on transition metal catalysts.