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 -C 6 H 4 CMe 3 )[H 2 NBn]X (X = Cl ( 7 ), Br ( 8 ), I ( 14 )) react reversibly with benzylamine in CDCl 3 at 25 °C via P( o -tolyl) 3 displacement to generate the corresponding bis(amine) derivatives trans -Pd( p -C 6 H 4 CMe 3 )[H 2 NBn] 2 X (X = Cl ( 17 ), K eq = 0.18 ± 0.02; Br ( 16 ), K eq = 0.14 ± 0.01; I ( 18 ), K eq = 0.10 ± 0.01). Complexes 16 − 18 were isolated from reaction of the palladium aryl halide dimers {Pd[P( o -tolyl) 3 ]( p -C 6 H 4 CMe 3 )(μ-X)} 2 (X = Cl ( 4 ), Br ( 5 ), I ( 6 )) and excess benzylamine as the corresponding mono(benzylamine) solvate Pd( p -C 6 H 4 CMe 3 )[H 2 NBn] 2 X·H 2 NBn (X = Br ( 16 ·H 2 NBn), Cl ( 17 ·H 2 NBn), I ( 18 ·H 2 NBn)). IR and 1 H NMR spectroscopy of 16 ·H 2 NBn 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 CD 2 Cl 2 to 3.6 ± 0.3 in THF- d 8 and in C 6 D 6 ranged from 0.90 ± 0.07 at 25 °C to 0.44 ± 0.04 at 77 °C (Δ G ° 298 K = 0.06 ± 0.01 kcal mol - 1; Δ H ° 298 K = −2.8 ± 0.1 kcal mol - 1; Δ S ° 298 K = −9 ± 1 eu). The equilibrium constants for the formation of the bis(amine) complexes Pd( p -C 6 H 4 CMe 3 )[amine] 2 Br from the reaction of Pd[P( o -tolyl) 3 ]( p -C 6 H 4 CMe 3 )[amine]Br and amine decreased in the order phenethylamine ≈ cyclohexylamine ≈ benzylamine ≈ (4-methylbenzyl)amine ≫ piperidine ≫ N -methylbenzylamine.