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 1 H 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 -C 6 H 4 Me)(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 -C 6 H 4 Me)(HNBn 2 )X (X = Cl ( 12 ), K = 6 ± 1 × 10 3 M - 1; X = Br ( 18 ), K = 3.5 ± 0.5 × 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)(μ-I)} 2 ( 21 ) to form Pd[P( o -tol) 3 ]( p -C 6 H 4 OMe)(HNBn 2 )I ( 24 ) provided the thermodynamic parameters Δ G 298 K = −3.1 ± 0.1 kcal mol - 1, Δ H 298 K = −11.9 ± 0.1 kcal mol - 1, and Δ S 298 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 -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 × 10 - 3 M - 1 ), respectively.