Wrackmeyer-type 1,1 carboboration is proposed to go through a zwitterionic intermediate, and this intermediate has been isolated and characterized in some cases. However, the mechanism can be highly substrate and reagent dependent.
In a borane, the compound typically adopts a trigonal planar molecular geometry, making the boron atom an electrophilic center. The substituents can affect the strength of the borane as a Lewis acid. Boranes which are stronger Lewis acids are better electrophiles and therefore better able to facilitate carboboration. Boranes can be optimized to work on less activated substrates. Tris(pentafluorophenyl)borane [B(CF)] is a strongly Lewis acidic borane which functions well in 1,1 carboborations with both activated and unactivated substrates, and it allows for the reaction to be facilitated with more mild conditions. An activated substrate such as an alkene or alkyne has an electron-withdrawing group directly attached to a carbon within the double or triple bond. Transition metal catalysts have been utilized to develop enantioselective 1,1 carboborations on unactivated alkenes. These reactions go through a catalytic cycle which may or may not go through a zwitterionic intermediate.