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 PhCH2Br (k1Br = 3.6 M−1 s−1) > PhCH2Cl (k1Cl = 6 × 10−3 M−1 s−1) at 29 °C. When the benzyl-Pd(IV) complex is generated from PhCH2Br, 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 (k2Br = 6 × 10−4 s−1) at 29 °C.