A Boron‐Fluorinated Tris(pyrazolyl)borate Ligand (FTp*) and Its Mono‐ and Dinuclear Copper Complexes [Cu(FTp*)2] and [Cu2(FTp*)2]: Synthesis, Structures, and DFT Calculations

AbstractReaction of [Si(3,5‐Me2pz)4] (1) with [Cu(MeCN)4][BF4] (2) gave the mono‐ and dinuclear copper complexes [Cu2(FTp*)2] (3) and [Cu(FTp*)2] (4). Both complexes contain the so‐far unprecedented boron‐fluorinated FTp* ligand ([FB(3,5‐Me2pz)3]− with pz=pyrazolyl) originating from 1, acting as a pyrazolyl transfer reagent, and the [BF4]− counter anion of 2, serving as the source of the {BF} entity. The solid‐state structures as well as the NMR and EPR spectroscopic characteristics of the complexes were elaborated. Pulsed gradient spin echo (PGSE) experiments revealed that 3 retains (almost entirely) its dimeric structure in benzene, whereas dimer cleavage and formation of acetonitrile adducts, presumably [Cu(FTp*)(MeCN)], is observed in acetonitrile. The short Cu⋅⋅⋅Cu distance of 269.16 pm in the solid‐state is predicted by DFT calculations to be dictated by dispersion interactions between all atoms in the complex (the Cu−Cu dispersion contribution itself is only very small). As revealed by cyclic voltammetry studies, 3 shows an irreversible (almost quasi‐reversible at higher scan rates) oxidation process centred at Epa=−0.23 V (E01/2=−0.27 V) (vs. Fc/Fc+). Oxidation reactions on a preparative scale with one equivalent of the ferrocenium salt [Fc][BF4] (very slow reaction) or air (fast reaction) furnished blue crystals of the mononuclear copper(II) complex [Cu(FTp*)2] (4). As expected for a Jahn–Teller‐active system, the coordination sphere around copper(II) is strongly distorted towards a stretched octahedron, in accordance with EPR spectroscopic findings.