Vanadium complexes having [VO]2+, [VO]3+ and [VO2]+ cores with hydrazones of 2,6-diformyl-4-methylphenol: synthesis, characterization, reactivity, and catalytic potential

Abstract

The Schiff bases H3dfmp(L)2 obtained by the condensation of 2,6-diformyl-4-methylphenol and hydrazones [L = isonicotinoylhydrazide (inh), nicotinoylhydrazide (nah) and benzoylhydrazide (bhz)] are prepared and characterized. By reaction of [V(IV)O(acac)2] and the H3dfmp(L)2 in methanol the V(IV)O-complexes [V(IV)O{Hdfmp(inh)2}(H2O)] (1), [V(IV)O{Hdfmp(nah)2}(H2O)] (2) and [V(IV)O{Hdfmp(bhz)2}(H2O)] (3) were obtained. Upon their aerial oxidation in methanol [V(V)O(OMe)(MeOH){Hdfmp(inh)2}] (4), [V(V)O(OMe)(MeOH){Hdfmp(nah)2}] (5) and [V(V)O(OMe)(MeOH){Hdfmp(bhz)2}] (6) were isolated. In the presence of KOH, oxidation of 1-3 results in the formation of [V(V)O2{H2dfmp(inh)2}]n·5H2O (7), K[V(V)O2{Hdfmp(nah)2}] (8) and K[V(V)O2{Hdfmp(bhz)2}] (9). All compounds are characterized in the solid state and in solution, namely by spectroscopic techniques (IR, UV-Vis, EPR, (1)H, (13)C and (51)V NMR), and DFT is also used to calculate the V(IV) hyperfine coupling constants of V(IV)-compounds and (51)V NMR chemical shifts of several V(V)-species and assign them to those formed in solution. Single crystal X-ray analysis of [V(V)O(OMe)(MeOH){Hdfmp(bhz)2}] (6) and [V(V)O2{H2dfmp(inh)2}]n·5H2O (7) confirm the coordination of the ligand in the dianionic (ONO(2-)) enolate tautomeric form, one of the hydrazide moieties remaining non-coordinated. In the case of 7 the free N(pyridine) atom of the inh moiety coordinates to the other vanadium center yielding a polynuclear complex in the solid state. It is also demonstrated that the V(V)O2-complexes are catalyst precursors in the oxidative bromination of styrene by H2O2, therefore acting as functional models of vanadium dependent haloperoxidases. Plausible intermediates involved in the catalytic process are established by UV-Vis, (51)V NMR and DFT studies.

Oxidation of secondary alcohols by conventional and microwave-assisted methods using molybdenum complexes of ONO donor ligands

“…Fig. 30 One water molecule in 1a, one methanol molecule in 3ÁDMSO and two oxido groups complete the coordination sphere. Selected bond distances and angles are given in Table 2.…”

“…[22][23][24] The cis-[Mo VI O 2 ] 2+ complexes of Schiff bases having ONO donor sites have drawn much attention due to their interesting catalytic properties. 30 Benzoyl hydrazide was prepared by the reaction of a twofold excess of hydrazine hydrate with ethyl benzoate in ethanol. The ligands H 3 dfmp(bhz) 2 I, H 3 dfmp(inh) 2 II and H 3 dfmp(nah) 2 III were prepared according to the reported method.…”

Thymol Bromination – A Comparison between Enzymatic and Chemical Catalysis

“…[10] Bromoperoxidases as catalysts for oxidative bromination have been reviewed. [4] A wide variety of vanadium complexes have been synthesized and used as functional models for V-haloperoxidases in order to have a better understanding of the mechanism of action of such enzymes, and these complexes are effective catalyst precursors in various oxidation reactions such as epoxidation of alkenes, oxidation of sulfides, alkanes, arenes and alcohols, as well as in oxidative bromination reactions in the presence of hydrogen peroxide [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] or alkyl hydroperoxides. [26] Inspired by the mechanism of action of V Br PO, a biphasic procedure for bromination reactions was proposed in 1994.…”

Thirty years through vanadium chemistry

“…My group has been mostly involved in the development of homogeneous and supported vanadium systems, mostly for catalytic epoxidations [165,167] and oxidations, namely of alkanes and alkenes [155,138,166,222,[253][254][255][256][257], of sulfides (sulfoxidations) [155,165,169,258,259,260], brominations [223,260,261], oxidative desulfurization [262], oxidative aminations [264] and hydroaminations [264]. Some of the processes involve homogeneous systems, others have addressed complexes supported in polystyrene [138,253,254,263] or encapsulated in zeolites [155,256].…”

“…A few of the processes involving vanadium catalysts were focused on asymmetric synthesis [165,166,169]. All cases involved the optimization of the experimental conditions for catalysis and in some cases the mechanisms of catalytic reaction were outlined and addressed namely by DFT calculations [165,167,169,260,262] which in many cases included the characterization of intermediate species, namely by 51 V NMR spectra measured in conditions simulating those prevailing during catalysis, and by theoretical calculation of the vanadium chemical shifts, to be compared with those observed experimentally.…”