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 (K-b) for the coordination of amines to the palladium fragment Pd[P(o-tol)(3)](p-C(6)H(4)Me)Cl were determined by H-1 NMR spectroscopy and decrease in the order hexylamine > benzylamine approximate to cyclohexylamine approximate to piperidine > dibutylamine approximate to diethylamine approximate to N-benzylmethylamine > morpholine > diisobutylamine > dibenzylamine approximate to ert-octylamine >> diisopropylamine > N-methylaniline. The palladium halide dimers {Pd[P(o-tol)(3)](p-C(6)H(4)Me)(mu-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-C(6)H(4)Me)(HNBn(2))X (X = Cl (12), K = 6 +/- 1 x 10(3) M(-1); X = Br (18), K = 3.5 +/- 0.5 x 10(3) 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-C(6)H(4)OMe)(mu-I)}(2) (21) to form Pd[P(o-tol)(3)](p-C(6)H(4)OMe)(HNBn(2))I (24) provided the thermodynamic parameters Delta G(298 K) = -3.1 +/- 0.1 kcal mol(-1), Delta H-298 K = -11.9 +/- 0.1 kcal mol(-1), and Delta S-298 K = 30 +/- 4 eu. Dimers 1-3 also react reversibly with diisopropylamine at 25 degrees C to form the amine adducts Pd[P(o-tol)(3)](p-C(6)H(4)Me)[HN(i-Pr-2)]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 x 10(-3) M(-1)), respectively.