Exploring the effect of hydroxylic and non-hydroxylic solvents on the reaction of [V^IVO(β-diketonate)₂] with 2-aminobenzoylhydrazide in aerobic and anaerobic conditions

Abstract

Refluxing [VO(β-diketonate)], namely [VO(acetylacetonate)] and [VO(benzoylacetonate)], separately with an equivalent or excess amount of 2-aminobenzoylhydrazide (ah) in laboratory grade (LG) CHOH in aerobic conditions afforded non-oxidovanadium(iv) and oxidovanadium(v) complexes of the type [V(L)] (1), [VO(L)(OCH)] (3) and [V(L)] (2), and [VO(L)(OCH)] (4), respectively. (L) and (L) represent the dianionic forms of 2-aminobenzoylhydrazone of acetylacetone (HL) and benzoylacetone (HL), respectively, (general abbreviation, HL), which was formed by the in situ condensation of ah with the respective coordinated [β-diketonate] in medium-to-good yield. The yield of different resulting products was dependent upon the ratio of ah to [VO(β-diketonate)]. For example, the yield of 1 and 2 complexes increased significantly associated with a decrease in the amount of 3 and 4 with an increase in the molar ratio of ah. Upon replacing CHOH by a non-hydroxylic solvent, LG CHCl, the above reaction yielded only oxidovanadium(v) complexes of the type [VO(L)(OH)] (5), [VO(L)(OH)] (6) and [VO(L)] (7, 8) whereas, upon replacing CHCl by another non-hydroxylic solvent, namely LG CHCN, only the respective [VO(L)] (7, 8) complex was isolated in 72-78% yield. However, upon performing the above reactions in the absence of air using dry CHOH or dry CHCl, only the respective [V(L)] complex was obtained, suggesting that aerial oxygen was the oxidising agent and the type of pentavalent product formed was dependent upon the nature of solvent used. Complexes 3 and 4 were converted, respectively, to 7 and 8 on refluxing in LG CHClvia the respective unstable complex 5 and 6. The DFT calculated change in internal energy (ΔE) for the reactions 2[VO(L)(OCH)] + 2HO → 2[VO(L)(OH)] + 2CHOH and 2[VO(L)(OH)] → [VO(L)] + HO was, respectively, +3.61 and -7.42 kcal mol, suggesting that the [VO(L)(OH)] species was unstable and readily transformed to the stable [VO(L)] complex. Upon one-electron reduction at an appropriate potential, each of 7 and 8 generated mixed-valence [(L)VO-(μ-O)-OV(L)] species, which showed valence-delocalisation at room temperature and localisation at 77 K. Some of the complexes showed a wide range of toxicity in a dose-dependent manner against lung cancer cells comparable with that observed with cis-platin.

Controlling Nuclearity and Stereochemistry in Vanadyl(V) and Mixed Valent VIV/VV Complexes of Oxido‐Pincer Pyridine‐2,6‐dimethanol Ligands

“…The EPR parameters for the pydim and pydip derivative are similar to those of related mononuclear O=V IV complexes, , , and comparable dinuclear compounds with class I valence‐isolated [OV IV (μ‐O)V V O] units , , , , . Similar valence delocalized (class II or III) behavior as found for [V 2 O 3 (pyphen) 2 ] · – has been previously reported for the radical anionic complexes [(L)OV IV (µ‐O)V V O(LO] · – with tridentate ONO 2– ligands based on hydroxy phenoxy hydrazides,, , , salenes, carboxy‐salicylaldiminates, or azophenolates,, and also the [OV IV (μ‐O oxido )(μ‐O phen )V V O] · 2+ complexes containing pentadentate (N′NONN′) 3– 2,6‐bis(phenoxymethyl‐ N , N ‐dimethylaminomethyl)aminomethyl)‐phenolates,, or complexes [(L)OV IV (µ‐O)V V O(LO] · 3+ complexes containing neutral N′NN′ ligands of the 2,6‐bis[benzimidazol‐2′‐yl]pyridine or ‐amine type, tris(2‐pyridylmethyl)amine, or 1,4,7‐triazacyclononane derivatives …”

“…The arrangement around the bridging O2 atom with V–O2–V angles of 117.1(3)° for the pydip complex and 129.5(6)° for the pyphen derivative revealing a syn‐angular configuration . Essential bond lengths show comparable values to other syn‐angular configured oxido‐bridged complexes with similar ligand systems (details in Tables S1 and S2, Supporting Information) …”

“…These bands are slightly red‐shifted for the vanadium complexes and some weak additional absorptions were observed at the edge to the visible region 300–500 nm (Figure and Table ), explaining the yellow color of the complexes. These absorptions can be assigned to ligand(oxido)‐to‐metal(V V ) LMCT transitions , , , …”