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 react reversibly with diisopropylamine at 25 °C to form the amine adducts Pd[P(o-tol)3](p-C6H4Me)[HN(i-Pr2)]X (X = Cl (17), K = 14 ± 3 M-1; X = Br (19), K = 2.8 ± 0.5 M-1; X = I (26), K = 6 ± 2 × 10-3 M-1), respectively.

Duke Scholars

Author Ross A. Widenhoefer Chemistry