Question

A Suzuki reaction requires palladium (0) to begin the catalytic cycle, yet this reaction uses palladium (II). Explain how palladium (II) is reduced to palladium (0) to start the reaction.

Answer 1

The Suzuki reaction uses Pd(0). However, the reaction starts with a Pd(II) species like Pd(PPh₃)₄ or Pd(PPh₃)₂Cl₂. The said Pd(II) species are known as catalyst precursors. The catalyst precursor is added to the reagent in presence of a base (like K₂CO₃ or trimethylamine, NEt₃). Triethyl amine also acts as the solvent in the reaction.

The solvent reduces Pd(II) to Pd(0) in situ. Pd(0) species are highly reactive and hence, must be generated in solution. The mechanism of reduction of Pd(II) to Pd(0) involves the addition of NEt₃ to Pd(II) to form a complex which undergoes dehydropalladation (loss of Pd(II)XH). The Pd(II)XH species undergoes reductive elimination with NEt₃ to form Pd (0).