Synthesis, Crystal Structure and Solution Behaviour of Palladium(II) Complexes with Tetrazenido or Amido Ligands and Potentially Tridentate Ligands

Pd(DBA)2 reacts with the azide C6F5N3 in the presence of terpy* to form the tetrazenido palladium(II) complex [(η2-terpy*)Pd{η2-N4(C6F5)2}] 1, whereas with TsN3 the amido complex [(η3-terpy*)Pd(NHTs)]+ is obtained. Another synthetic route involving abstraction of chloride ions from [(L)PdCl]Cl and transmetallation with KNHTs yields the complexes [(η3-L)Pd(NHTs)](BF4) (4: L = terpy*; 5: L = triphos). Compounds 1, 4 and 5 have been characterized in the solid state by single-crystal X-ray analysis as mononuclear, square-planar complexes. 1H and 19F NMR spectroscopy reveal that 1 is a fluxional molecule. Rotation of both C6F5 rings is hindered, with energy barriers of 53.9 kJ·mol−1 (293 K) and 60.7 kJ·mol−1 (325 K). Additionally, the lateral pyridines and the C6F5 rings exchange through an oscillatory process where one terminal pyridine enters the coordination sphere while the other leaves it. The corresponding energy barrier (74.9 kJ·mol−1 at 298 K) has been determined from selective inversion NMR experiments.