Homoleptic complexes of vanadium and N-heterocycles made via oxidation of vanadium nanoparticles

The four homoleptic coordination compounds [NaV(cbz)₄] (1), [V(bipy)₃] (2), [V(phen)₃] (3), and [V(Hai)₃(ai)₂]·0.5 tol (4) are prepared by the reaction of vanadium metal (V(0)) nanoparticles (mean size: 1.6 ± 0.3 nm) with the sterically demanding N-H-acidic/non-N-H-acidic, chelating/non-chelating aromatic N-heterocycles carbazole (Hcbz), 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), and 7-azaindole (Hai). The V(0) nanoparticles are used as a reactive starting material to perform redox reactions with the N-heterocycles in toluene (tol) at 80-120 °C. The V(0) nanoparticles and the compounds 1-4 are characterized by X-ray diffraction (single crystals and powders), electron microscopy (TEM and STEM), spectroscopic methods (FT-IR and UV-Vis), and thermal analysis (TG). Besides the first use of V(0) nanoparticles in reactions with N-heterocycles, the underlying redox reactions result in new homoleptic V(II)/V(III) coordination compounds with the respective N-heterocycles as sole ligands. All coordinated N-heterocycles serve as monovalent anions with the N-H-acidic Hcbz and Hai being deprotonated leading to the formation of hydrogen, whereas the non-N-H-acidic bipy and phen are directly reduced with the oxidation of vanadium. Most interesting is compound 4 with three different coordination scenarios of the Hai/ai^- ligand, resulting in a composition [V(η¹-Hai)₃(η²-ai)(η¹-ai)]·0.5tol, which is observed here for the first time.