Synthesis and Characterization of Potassium Complexes Containing Terminal η2‐Pyrazolato Ligands

Abstract

AbstractThe potassium complexes [K(η2‐3,5‐R2pz)(η6‐18‐crown‐6)] (R = Ph, tBu; pz = pyrazolato) were prepared by treatment of 3,5‐diphenylpyrazole or 3,5‐di‐tert‐butylpyrazole with potassium hydride in the presence of 18‐crown‐6. These complexes contain η6‐18‐crown‐6 and terminal η2‐pyrazolato ligands, and constitute the first examples of group 1 metal complexes with this pyrazolato ligand coordination mode. In contrast to [K(η2‐3,5‐Ph2pz)(η6‐18‐crown‐6)] and [K(η2‐3,5‐tBu2pz)(η6‐18‐crown‐6)], the aqua complex [K(η2‐3,5‐Me2pz)(H2O)(η6‐18‐crown‐6)] was obtained when 3,5‐dimethylpyrazole was treated with potassium hydride and 18‐crown‐6 in the presence of a small amount of water. [K(η2‐3,5‐Me2pz)(H2O)(η6‐18‐crown‐6)] contains an η2‐pyrazolato ligand that is bent towards being co‐facial with the best plane of the 18‐crown‐6 ligand, to allow hydrogen bonding between the pyrazolato ligand nitrogen atoms and the coordinated aqua ligand. The hydrogen bonding thus confers a novel terminal π‐facial η2‐bonding mode to the pyrazolato ligand. All compounds were characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)