Vanadate complexes bearing an imidazolidine-bridged bis(aryloxido) ligand: synthesis and solid state and solution structure

Abstract

A new imidazolidine-bridged bis(aryloxido) ligand precursor (H₂2L) [H₂2L = 2,2′-(imidazolidine-1,3-diylbis(methylene))bis(4-(1,1,3,3-tetramethylbutyl-2-yl)phenol)] was prepared in a relatively high yield (∼60%) via a single-step Mannich condensation of 4-(1,1,3,3-tetramethylbutyl)phenol, ethylenediamine and paraformaldehyde at 2 : 1 : 3 molar ratio and characterized by chemical and physical techniques including X-ray crystallography. Reactions of H₂2L with [VO(OEt)₃] at 1 : 1 and 1 : 2 molar ratios in toluene afforded [V(L-κ³O,N,N,O)(O)(OEt)] (1) and [V₂(μ-L-κ⁴O,N,N,O)(μ-OEt)₂(O)₂(OEt)₂] (2), respectively. Alcoholysis of 1 with EtOH enables elimination of one molecule of H₂2L and the formation of 2. Compounds 1 and 2 were characterized by IR and NMR spectroscopy as well as ES-MS experiments. The definitive molecular structure of 2 was provided by a single-crystal analysis and revealed its dinuclear nature, featuring two octahedral vanadium centres bridged by both OEt groups and the L ligand. The ⁵¹V, ¹H and ¹³C NMR spectra as well as ES-MS showed that 2 does not stay intact in solution and undergoes dissociation to give 1 and [VO(OEt)₃].