Second- and inverse order pathways in the mechanism of orthopalladation of primary amines

The orthopalladation of benzylamine (baH) by Pd(II) acetate in acetonitrile occurs in two time-resolved steps. A first faster step taking place at 25 °C results in the formation of the N-bound complex [Pd(OAc)2(baH)2] and follows a second-order kinetics in the incoming amine according to the rate law kobs=k1[baH]2. The second order in baH arises from the successive substitution of the solvent in [Pd(OAc)2(MeCN)2]. The latter complex transforms slowly into the orthometalated derivative [Pd(ba)(OAc)]2 at 60 °C. The initial rate of this step is inversely proportional to the concentration of baH and the following rate law holds: . This is accounted for in terms of the mechanism involving a reversible dissociation of one baH ligand from [Pd(OAc)2(baH)2] followed by the electrophilic CH bond cleavage of N-bound baH by Pd(II).