Rates of the Oxidative Addition of Benzyl Halides to a Metallacyclic Palladium(II) Complex and of the Reductive Elimination from a Benzyl-Palladium(IV) Complex

Pd(II) metallacyclic complexes are key intermediates in sequential reactions in which three new C−C bonds are formed in an aromatic ring. The Pd(II) metallacyclic complex 10 with phenanthroline as ligand undergoes oxidative addition to benzyl bromide or chloride in DMF to generate benzyl-Pd(IV) complexes. The rate constant of the oxidative addition is determined by means of electrochemical techniques, with the expected reactivity order PhCH 2 Br ( k 1Br = 3.6 M −1 s −1 ) > PhCH 2 Cl ( k 1Cl = 6 × 10 −3 M −1 s −1 ) at 29 °C. When the benzyl-Pd(IV) complex is generated from PhCH 2 Br, the oxidative addition is followed by a slow C−C reductive elimination, which gives a Pd(II) complex. The rate constant of the reductive elimination has been determined in DMF ( k 2Br = 6 × 10 −4 s −1 ) at 29 °C.