One compound, two structures:: synthesis, structures and reactivity of a novel (tripyrrinato)palladium(II) trifluoracetate complex TrpyPdOAcf

The novel (2,15-dimethyl-3,4,13,14-tetraethyltripyrrinato)palladium(II) trifluoroacetate (TrpyPdOAc(f)) 7 was found to exhibit two different geometries in the solid state. While in one crystal the tripyrrin ligand is helically distorted to ensure a square-planar coordination of the central palladium(II) ion, the bonding geometry of the metal centre of the other geometrical isomer found in a different crystal showed a pronounced tetrahedral deviation from planarity, accompanied with an almost planar tripyrrolic ligand. In solution, non-planar structures of 7 can not be detected, as judged by the results of variable temperature proton NMR spectroscopy. The energy stored in the strained complexes 6 and 7, however, becomes "visible" in fast ligand exchange processes, which enable us to prepare a number of new TrpyPdX complexes with X = Cl, Br, I, N-3, NCO, SCN and OAc, of which the latter two decompose in solution. As the X-ray crystallographic analysis of TrpyPdBr 9 demonstrates, complexes with a tilted fourth ligand are predominant in the solid state with donor atoms larger than oxygen.