Homoleptic Complexes of Vanadium and N-Heterocycles Made via Oxidation of Vanadium Nanoparticles

Abstract

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 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 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, STEM), spectroscopic methods (FT-IR, UV-Vis), and thermal analysis (TG). Beside 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 with formation of hydrogen, whereas the non-N–H-acidic bipy and phen are directly reduced with 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)]·tol, which is here observed for the first time.