Stille Cross-Coupling Reactions

The Still cross-coupling reaction is a catalytic cycle. The first step is the reduction of the palladium (Pd) catalyst resulting in the active Pd(0) species was a result of dissociation of ligands. Then, the oxidative addition of the organohalide (an organic molecule with a halide) gives a cis intermediate. This intermediate is very unstable so it rapidly isomerizes to form the trans intermediate. Transmetalation (or ligand-exchange) has the general form M1-R + M2-X → M1-X + M2-R, where R and R' can be, but are not limited to, an alkyl, aryl, alkynyl, allyl, halogen, or pseudo-halogen groups. The ligand is transferred via an intermolecular mechanism and one metal is oxidized where as the other is reduced. Transmetalation with the organostannane (a compound based on tin (Sn) with hydrocarbon substituents) forms an intermediate. After reductive elimination, this produces the desired product and the active Pd(0) species once again. In this reaction, the oxidative addition and reductive elimination retain the stereochemical configuration of the respective reactants.