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

Reaction of [Si(3,5‐Me 2 pz) 4 ] ( 1 ) with [Cu(MeCN) 4 ][BF 4 ] ( 2 ) gave the mono‐ and dinuclear copper complexes [Cu 2 ( F Tp*) 2 ] ( 3 ) and [Cu( F Tp*) 2 ] ( 4 ). Both complexes contain the so‐far unprecedented boron‐fluorinated F Tp* ligand ([FB(3,5‐Me 2 pz) 3 ] − with pz=pyrazolyl) originating from 1 , acting as a pyrazolyl transfer reagent, and the [BF 4 ] − 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( F Tp*)(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 E pa =−0.23 V ( E 0 1/2 =−0.27 V) (vs. Fc/Fc + ). Oxidation reactions on a preparative scale with one equivalent of the ferrocenium salt [Fc][BF 4 ] (very slow reaction) or air (fast reaction) furnished blue crystals of the mononuclear copper(II) complex [Cu( F Tp*) 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.