Palladium round trip in the Negishi coupling of trans-[PdMeCl(PMePh2)2] with ZnMeCl: An experimental and DFT study of the transmetalation step

The large rate difference of the slow reductive elimination and the fast transmetalation-retrotransmetalation steps allows Pd to visit complexes 3, 2, and 1 many times before coupling from 2 takes place. This fast recurrence of transformations offers many opportunities for the formation of undesired homocoupling products in Negishi reactions by statistically accessible “mistaken” retrotransmetalation events in the multitude of processes preceding the slower irreversible reductive elimination of the coupling product.