Coordination chemistry of non-oxido, oxido and dioxidovanadium(IV/V) complexes with azine fragment ligands

Oxidovanadium complexes with tridentate aroylhydrazone as catalyst precursors for solvent-free microwave-assisted oxidation of alcohols

“…Complex 3 was also identified by the 51 V NMR spectroscopy ( Table 1). The spectrum shows characteristic peak at −478 ppm corresponds to oxidiovanadium(V) centre [48].…”

“…1). The vanadium ion exhibits a distorted octahedral O 4 N 2 coordination (quadratic elongation of 1.048 and angle variance of 104.79 [48,59], the four vanadium oxygen bond lengths in 3 follow the order: oxido < phenolate < enolate. Fig.…”

“…Complexes It is well known that [VO(acac) 2 ] undergoes aerial oxidation in solution (preferably in alcohol medium) in the presence of hydrazone Schiff bases [48,57,58]. Sometimes, the presence of a neutral bidentate N,N donor auxiliary ligand in CH 3 CN helps to stabilize the oxidovanadium(IV) centre, which can be isolated as a stable solid product [59,60].…”

“…Sometimes, the presence of a neutral bidentate N,N donor auxiliary ligand in CH 3 CN helps to stabilize the oxidovanadium(IV) centre, which can be isolated as a stable solid product [59,60]. Herein, we used two different bidentate auxiliary ligands to stabilize oxidovanadium centres in 3 and 4: the mono negative 8-hydroxyquinolinate (hq − ) and the neutral 1,10-phenanthroline (phen) which stabilize the vanadium(V) and the vanadium(IV) centre, respectively, with the tridentate hydrazone Schiff base [48,59,60]. The four complexes of this study (1-4) present different coordination environments and have been used for a comparative study of their catalytic activities towards solventfree MW-assisted oxidation of secondary alcohols.…”

“…On the other hand, aroylhydrazones are known to form stable complexes with vanadium in +4 or +5 oxidation states [44][45][46][47][48]. Therefore, the main objective of the present study was to establish the viability of oxidovanadium complexes based on an aroylhydrazone ligand as possible catalyst precursors for alcohols oxidation under the above conditions (in the absence of added solvent and under MW irradiation).…”