Formation of palladium bis (amine) complexes from reaction of amine with palladium tris(o-tolyl)phosphine mono(amine) complexes

Palladium mono(benzylamine) complexes Pd[P(o-tolyl)3](p-C6H4CMe3)[H 2NBn]X (X = Cl (7), Br (8), I (14)) react reversibly with benzylamine in CDCl3 at 25 °C via P(o-tolyl)3 displacement to generate the corresponding bis(amine) derivatives trans-Pd(p-C6H4CMe3)[H2-NBn]2X (X = Cl (17), Keq = 0.18 ± 0.02; Br (16), Keq = 0.14 ± 0.01;I (18), Keq = 0.10 ± 0.01). Complexes 16-18 were isolated from reaction of the palladium aryl halide dimers {Pd[P(o-tolyl)3](p-C6H4CMe 3)(μ-X)}2 (X = Cl (4), Br (5), I (6)) and excess benzylamine as the corresponding mono(benzylamine) solvate Pd(p-C6H4CMe3)[H2NBn] 2X·H2NBn (X = Br (16·H2NBn), Cl (17·H2NBn), I (18·H2NBn)). IR and 1H NMR spectroscopy of 16·H2NBn indicated the presence of N-H⋯X (X = N, Br, Pd) hydrogen bonds in both the solid state and solution. The equilibrium constant for the formation of 16 and P(o-tolyl)3 from 8 and benzylamine ranged from 0.066 ± 0.005 in CD2Cl2 to 3.6 ± 0.3 in THF-d8 and in C6D6 ranged from 0.90 ± 0.07 at 25 °C to 0.44 ± 0.04 at 77 °C (ΔG°298K = 0.06 ± 0.01 kcal mol-1; ΔH°298K=-2.8 ± 0.1 kcal mol 1; ΔS°298K = -9 ± 1 eu). The equilibrium constants for the formation of the bis(amine) complexes Pd(p-C6H4CMe3)[amine]2Br from the reaction of Pd[P(o-tolyl)3]-(p-C6H4Me 3)[amine]2Br and amine decreased in the order phenethylamine ≈ cyclohexylamine ≈ benzylamine ≈ (4-methylbenzyl)amine ≫ piperidine ≫ N-methylbenzylamine.

Duke Scholars

Author Ross A. Widenhoefer Chemistry