Various pyrazole‐based P,N (2a–c) and N,N (3a–b) ligands have been synthesized. Using representative ligands, NiII, CoII, CuII, and CuI complexes have been prepared and structurally characterized by crystallography. During complexation of CoII and CuII salts, the phosphane part of the P,N ligand oxidized to phosphane oxide. For N,N donor ligands, a dimeric chloro‐bridged NiII complex was obtained. NiII complex 4 is an active catalyst for ethylene oligomerization. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)