Kinetics and Mechanism of the Formation of Palladium Bis(benzylamine) Complexes from Reaction of Benzylamine with Palladium Tri-o-tolylphosphine Mono(amine) Complexes
The kinetics of the conversion of the palladium mono(benzylamine) complex Pd[P(o-tol)3](p-C6H4CMe3)[H 2-NBn]Br (2) to the bis(benzylamine) complex Pd(p-C6H4CMe3[H2NBn]2Br (3) established the second-order rate law: Rate = k1[H2NBn], where ΔH‡ = 13.8 ± 0.3 kcal mol-1 and ΔS‡ = -29.7 ± 0.8 eu. Kinetics were consistent with a mechanism initiated by direct attack of benzylamine on 2 via an associative or interchange mechanism. Benzylamine exchange with both 2 and 3 was > 1.5 × 103 times faster than conversion of 2 to 3 under comparable conditions. Complex 2 underwent phosphine exchange in the presence of P(1-naphthyl)3 to form Pd[P(1-naphthyl)3](p-C6H4CMe 3)[H2NBn]Br (9). Kinetics of the conversion of 9 to 2 were consistent with associative solvolysis of 9 to form Pd[P(1-naphthyL)3](p-C6H4CMe 3)[solvent]Br (V) followed by attack of P(o-tolyl)3 to form the mixed bis(phosphine) intermediate Pd[P(o-tol)3][P(1-naphthyl)3](p-C6H 4CMe3)Br (VI). Solvolytic displacement of P(o-tolyl)3 from VI followed by reaction with amine would then form 2.