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

Abstract 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 k obs = k 1 [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: V 0 =k m Pd ( II ) t /[ baH ] . 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).