Investigation of the Ligand Exchange Behavior of Square‐Planar Nickel(II) Complexes by X‐ray Absorption Spectroscopy and X‐ray Diffraction

The local structure of nickel and bromine in three square‐planar nickel( II ) complexes [(2,2′‐bipyridyl)(bromo)(mesityl)nickel( II )] ( 1 ), [(bromo)( N , N ‐diisopropyl‐1,2‐ethanediimine)(mesityl)nickel( II )] ( 2 ), [(bromo)(mesityl)bis(triphenylphosphane)nickel( II ) ( 3 )] and their ligand exchange behavior towards several solvents has been determined by means of X‐ray Absorption Near Edge Spectroscopy (XANES), Extended X‐ray Absorption Fine Structure Spectroscopy (EXAFS), X‐ray Diffraction (XRD), multinuclear NMR and UV/Vis spectroscopy. Several square‐planar and octahedral nickel( II ) complexes were prepared and spectroscopically characterized as reference compounds. The exchange behavior strongly depends on the nature of the incoming donor ligand (solvent molecule). In some cases the substitution of one or more ligands was accompanied by conservation of the square‐planar geometry. In other solvents the geometry changed from square‐planar to octahedral. The structural information obtained is important to the further development of such nickel( II ) complexes as catalysts for various applications. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)