Chemistry of Monomeric and Dinuclear Non-Oxido Vanadium(IV) and Oxidovanadium(V) Aroylazine Complexes: Exploring Solution Behavior

Abstract

A series of mononuclear non-oxido vanadium(IV) [V(IV)(L(1-4))2] (1-4), oxidoethoxido vanadium(V) [V(V)O(L(1-4))(OEt)] (5-8), and dinuclear μ-oxidodioxidodivanadium(V) [V(V)2O3(L(1))2] (9) complexes with tridentate aroylazine ligands are reported [H2L(1) = 2-furoylazine of 2-hydroxy-1-acetonaphthone, H2L(2) = 2-thiophenoylazine of 2-hydroxy-1-acetonaphthone, H2L(3) = 1-naphthoylazine of 2-hydroxy-1-acetonaphthone, H2L(4) = 3-hydroxy-2-naphthoylazine of 2-hydroxy-1-acetonaphthone]. The complexes are characterized by elemental analysis, by various spectroscopic techniques, and by single-crystal X-ray diffraction (for 2, 3, 5, 6, 8, and 9). The non-oxido V(IV) complexes (1-4) are quite stable in open air as well as in solution, and DFT calculations allow predicting EPR and UV-vis spectra and the electronic structure. The solution behavior of the [V(V)O(L(1-4))(OEt)] compounds (5-8) is studied confirming the formation of at least two different types of V(V) species in solution, monomeric corresponding to 5-8, and μ-oxidodioxidodivanadium [V(V)2O3(L(1-4))2] compounds. The μ-oxidodioxidodivanadium compound [V(V)2O3(L(1))2] (9), generated from the corresponding mononuclear complex [V(V)O(L(1))(OEt)] (5), is characterized in solution and in the solid state. The single-crystal X-ray diffraction analyses of the non-oxido vanadium(IV) compounds (2 and 3) show a N2O4 binding set and a trigonal prismatic geometry, and those of the V(V)O complexes 5, 6, and 8 and the μ-oxidodioxidodivanadium(V) (9) reveal that the metal center is in a distorted square pyramidal geometry with O4N binding sets. For the μ-oxidodioxidodivanadium species in equilibrium with 5-8 in CH2Cl2, no mixed-valence complexes are detected by chronocoulometric and EPR studies. However, upon progressive transfer of two electrons, two distinct monomeric V(IV)O species are detected and characterized by EPR spectroscopy and DFT calculations.

Versatile Reactivity and Theoretical Evaluation of Mono- and Dinuclear Oxidovanadium(V) Compounds of Aroylazines: Electrogeneration of Mixed-Valence Divanadium(IV,V) Complexes

“…The lower-energy absorptions in the range 435− 420 nm are ascribed to the ligand-to-metal charge-transfer transitions, while the higher-energy absorptions in the range 340−235 nm are likely to be due to ligand-centered transitions. 12b, 30 The electronic spectra depict similar features but do not allow clear conclusions regarding the possibility of the existence of mononuclear− dinuclear equilibria.…”

“…This indicates that, along with monomeric species, the complexes may exist as an isolated dinuclear μ-oxido (second species) in solution, as reported in other recent publications. 12f, 30 On the basis of the above results, the mentioned solution behavior of 1−4 should be ascribed to the equilibria in Scheme 3 existing in chloroform/DMSO/MeCN−DMSO containing a small amount of water, which also explains the simultaneous presence of the two species M V (monomer, isolated in the solid state and characterized by single-crystal XRD) and M V -M V (second species, proposed as a dinuclear μ-oxido complex) in solution.…”

Vanadium Complexes Derived from Acetyl Pyrazolone and Hydrazides: Structure, Reactivity, Peroxidase Mimicry and Efficient Catalytic Activity for the Oxidation of 1‐Phenylethanol

“…A quasi‐reversible peak at ca. 1.33 V, as well as the associated coupled peak at 1.16 V, are due to a V IV → V V conversion . No reduction process assignable to V III → V II was observed in any voltammogram.…”

Reactivity and Catalytic Activity of Homobimetallic Vanadium(V) Complex Derived from Bis(5‐chlorosalicylaldehyde)oxaloyldihydrazone Ligand

“…The absorption band of the complex at 423 nm shows a decrease in the intensity, but other ligand bands suffer blue or red shift on titration with H 2 O 2. When further amount of H 2 O 2 is added to the complex solution in methanol, an increase in the intensity of the band at 305 nm with a blue shift to 303 nm, and the band at 335 nm with a red shift to 341 nm, respectively. The continuous addition of 30% H 2 O 2 also show the presence of one isosbestic point at 372 nm in the complex.…”