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 degreesC 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 degreesC. The initial rate of this step is inversely proportional to the concentration of baH and the following rate law holds: V, = 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). (C) 2002 Elsevier Science B.V. All rights reserved.