Halide and Amine Influence in the Equilibrium Formation of Palladium Tris(o-tolyl)phosphine Mono(amine) Complexes from Palladium Aryl Halide Dimers

The relative binding constants (Kb) for the coordination of amines to the palladium fragment Pd[P(o-tol)3](p-C6H4Me)Cl were determined by 1H NMR spectroscopy and decrease in the order hexylamine > benzylamine ≈ cyclohexylamine ≈ piperidine > dibutylamine ≈ diethylamine ≈ N-benzylmethylamine > morpholine > diisobutylamine > dibenzylamine ≈ tert-octylamine >> diisopropylamine > N-methylaniline. The palladium halide dimers {Pd[P(o-tol)3](p-C6H4Me)(μ-X)}2 (X = Cl (1), Br (2), I (3)) react reversibly with dibenzylamine to generate the corresponding 1:1 palladium amine adducts Pd[P(o-tol)3](p-C6H4Me)(HNBn2)X (X = Cl (12), K = 6 ± 1 × 103 M-1; X = Br (18), K= 3.5 ± 0.5 × 103 M-1; X = I (22), K = 90 ± 20 M-1), respectively. The related reaction of dibenzylamine with the iodide dimer {Pd[P(o-tol)3](p-C6H4OMe)(μ-I)}2 (21) to form Pd[P(o-tol)3](p-C6H4OMe)(HNBn2)I (24) provided the thermodynamic parameters ΔG298 K = −3.1 ± 0.1 kcal mol-1, ΔH298 K = −11.9 ± 0.1 kcal mol-1, and ΔS298 K = −30 ± 4 eu. Dimers 1−3 also rea...