OBSERVATION OF A SLOW DISSOCIATIVE PROCESS IN PALLADIUM(II) COMPLEXES

The dynamic behavior of complexes [Pd(C6F5)X(SPPy(n)Ph(3-n))] (Py = py ridin-2-yl; X = Br, n = 1 (1), 3 (3); n = 2, X = Cl (2a), Br (2b), I ( 2c)) has been studied by NMR spectroscopy. Complex 1 has a S,N-chelati ng ligand and shows no isomers. Complexes 2 show two isomers, N,N- and N,S-bonded, the latter being dominant (>95%). Rotation of the C6F5 gr oup in the N,S-isomers in CDCl3 occurs slowly with Delta H double dagg er (kJ mol(-1)) = 60.0 (2a), 57.1 (2b), 50.2 (2c) and Delta S double d agger (J K-1 mol(-1)) = -35.8 (2a), -37.5 (2b), -51.1 (2c). Evidence s trongly supports that this rotation is severely hindered in a square-p lanar complex and occurs in a contact ion pair [Pd(C6F5)(SPPy(2)Ph-N,S )]. X formed by halide dissociation. Complex 3 shows also two isomers, and its N,N-isomer shows apparent C6F5 rotation corresponding in real ity to exchange of the Py group trans to the Pd-C bond and the uncoord inated Py group. The structure of [Pd(C6F5)Br(SPPy(2)Ph-N,S)] has been studied by X-ray diffraction: P2(1)/c, a = 8.273(2) Angstrom, b = 14. 240(2) Angstrom, c = 19.547(4) Angstrom, beta = 95.10(2)degrees, V = 2 293.6(7) Angstrom(3), Z = 4.