Novel Oxidovanadium Complexes with Redox-Active R-Mian and R-Bian Ligands: Synthesis, Structure, Redox and Catalytic Properties

Abstract

A new monoiminoacenaphthenone 3,5-(CF3)2C6H3-mian (complex 2) was synthesized and further exploited, along with the already known monoiminoacenaphthenone dpp-mian, to obtain oxidovanadium(IV) complexes [VOCl2(dpp-mian)(CH3CN)] (3) and [VOCl(3,5-(CF3)2C6H3-bian)(H2O)][VOCl3(3,5-(CF3)2C6H3-bian)]·2.85DME (4) from [VOCl2(CH3CN)2(H2O)] (1) or [VCl3(THF)3]. The structure of all compounds was determined using X-ray structural analysis. The vanadium atom in these structures has an octahedral coordination environment. Complex 4 has an unexpected structure. Firstly, it contains 3,5-(CF3)2C6H3-bian instead of 3,5-(CF3)2C6H3-mian. Secondly, it has a binuclear structure, in contrast to 3, in which two oxovanadium parts are linked to each other through V=O···V interaction. This interaction is non-covalent in origin, according to DFT calculations. In structures 2 and 3, non-covalent π-π staking interactions between acenaphthene moieties of the neighboring molecules (distances are 3.36–3.40 Å) with an estimated energy of 3 kcal/mol were also found. The redox properties of the obtained compounds were studied using cyclic voltammetry in solution. In all cases, the reduction processes initiated by the redox-active nature of the mian or bian ligand were identified. The paramagnetic nature of complexes 3 and 4 has been proven by EPR spectroscopy. Complexes 3 and 4 exhibited high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The yields of products of cyclohexane oxidation were 43% (complex 3) and 27% (complex 4). Based on the data regarding the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play the most crucial role in the reaction. The initial products in the reactions with alkanes are alkyl hydroperoxides, which are easily reduced to their corresponding alcohols by the action of triphenylphosphine (PPh3). According to the DFT calculations, the difference in the catalytic activity of 3 and 4 is most likely associated with a different mechanism for the generation of ·OH radicals. For complex 4 with electron-withdrawing CF3 substituents at the diimine ligand, an alternative mechanism, different from Fenton’s and involving a redox-active ligand, is assumed.

Noncovalent Dualism in Perylene-Diimide-Based Keggin Anion Complexes: Theoretical and Experimental studies

“…The electron density values at these bond critical points are from 0.003 to 0.011 atomic units, with positive values of the Laplacian of electron density (0.011–0.046 atomic units) and energy density close to zero (0.001–0.002 au). These characteristics, along with the estimated strength of the short contacts, ranging from 0.3 to 2.2 kcal/mol per contact, are typical for stacking interactions in similar chemical systems. ,− The balance between the Lagrangian kinetic energy G ( r ) and potential energy density V ( r ) at the bond critical points (3, −1) (with a ratio – G ( r )/ V ( r ) > 1) reveals the absence of a significant covalent contribution in the intermolecular interactions O···C and C···C within the X-ray structures 2085758 , 2085793 , complex 2 , per_Et2 , and per_Me2 . (Table S6).…”

Gold(i) complexes with redox active BIAN and MIAN ligands: synthesis, structure and electrochemistry

“…This is consistent with monoimine (MIAN) being a stronger oxidizing agent than diimine (BIAN). [50][51][52] Crystal structure…”

Mono(arylhydrazino)acenaphthenones as a platform for the design of NIR chromophores based on Pd(ii)-BIAN complexes

“…Their key feature is the ability to accept up to four electrons and reversibly exchange them with the coordinating metal, which makes it possible to trigger various redox transformations. [16][17][18][19][20][21][22][23][24] Square-planar transition metal complexes containing both p-donor and p-acceptor ligands belong to the so-called pushpull systems. To date, push-pull metal complexes have been significant objects of research for many scientific groups of chemists and materials scientists.…”

“…Their key feature is the ability to accept up to four electrons and reversibly exchange them with the coordinating metal, which makes it possible to trigger various redox transformations. 16–24…”