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 (k(1Br) = 3.6 M-1 s(-1)) > PhCH2Cl (k(1Cl) = 6 x 10(-3) M-1 s(-1)) at 29 degrees 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 (k(2Br) = 6 x 10(-4) s(-1)) at 29 degrees C.