Exploring the coordination chemistry of 1-benzoyl-4,5-dihydro-3,5-bis(trifluoromethyl)-1H-pyrazol-5-ol to copper

The coordination chemistry of the ligand 1-benzoyl-4,5-dihydro-3,5-bis(trifluoromethyl)-1H-pyrazol-5-ol (1a) has been recently investigated. In dependency of the metal (e.g., nickel, zinc, molybdenum) and the added co-ligand (phosphanes, pyridines, amines) different coordination modes were feasible (e.g., O,N,O′, O,N, O,O′). Herein we present the reaction of 1a with Cu(OAc)2 and triphenylphosphane as co-ligand to form the copper complex 2 [Cu(1a-H)(PPh3)2]. The complex was characterized and investigated by various techniques, pointing out a new bidentate coordination mode of the ligand. In more detail, X-ray crystallography determined a N,O-coordination in which the ligand is planar and the other coordination sites on the copper centre are occupied by two PPh3 creating a tetrahedral coordination geometry. Moreover, the complex has been applied as precatalyst in the copper-catalyzed amination of aliphatic C–H bonds.