Synthesis, characterisation and catalytic potential of hydrazonato-vanadium(V) model complexes with [VO]3+ and [VO2]+ cores.
Reaction between [VO(acac)2] and H2L (H2L are the hydrazones H2sal-nah I or H2sal-fah II; sal = salicylaldehyde, nah = nicotinic acid hydrazide and fah = 2-furoic acid hydrazide) in methanol leads to the formation of oxovanadium(IV) complexes [VOL.H2O](H2L = I: 1, H2L = II: 4). Aerial oxidation of the methanolic solutions of 1 and 4 yields the dinuclear oxo-bridged monooxovanadium(V) complexes [{VOL}2mu-O](H2L = I: 2, H2L = II: 5). These dinuclear complexes slowly convert, in excess methanol, to [VO(OMe)(MeOH)L](H(2)L = I: 9, H(2)L = II: 10), the crystal and molecular structures of which have been determined, confirming the ONO binding mode of the dianionic ligands in their enolate form. Reaction of aqueous K[VO3] with the ligands at pH ca. 7.5 results in the formation of [K(H2O)][VO2L](H2L = I: 3, H2L = II: 6). Treatment of 3 and 6 with H2O2 yields (unstable) oxoperoxovanadium(v) complexes K[VO(O2)L], the formation of which has been monitored spectrophotometrically. Acidification of methanolic solutions of 3 and 6 with HCl affords oxohydroxo complexes, while the neutral complexes [VO2(Hsal-nah)] 7 and [VO2(Hsal-fah)] 8 were isolated on treatment of aqueous solutions of 3 and 6 with HClO4. These complexes slowly transform into 9 and 10 in methanol, as confirmed by 1H, 13C and 51V NMR. The anionic complexes 3 and 6 catalyse the oxidative bromination of salicylaldehyde in water in the presence of H2O2/KBr to 5-bromosalicylaldehyde and 3,5-dibromosalicylaldehyde, a reaction similar to that exhibited by vanadate-dependent haloperoxidases. They are also catalytically active for the oxidation of benzene to phenol and phenol to catechol and p-hydroquinone.
Maurya
Mannar R
MR
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, 247 667, India. rkmanfcy@iitr.ernet.in
Agarwal
Shalu
S
Bader
Cerstin
C
Ebel
Martin
M
Rehder
Dieter
D
D000447:Aldehydes / Q000737:chemistry; D001554:Benzene / Q000737:chemistry; D001965:Bromides / Q000737:chemistry; D002384:Catalysis; D002396:Catechols / Q000737:chemistry; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D006835:Hydrazones / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000737:chemistry; D008024:Ligands; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D019800:Phenol / Q000737:chemistry; D014639:Vanadium / Q000737:chemistry* / Q000378:metabolism; D017968:Vanadium Compounds / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism
D000447:Aldehydes; D001965:Bromides; D002396:Catechols; D006835:Hydrazones; D008024:Ligands; D017968:Vanadium Compounds; D014639:Vanadium; C013243:salicylaldehyde; D019800:Phenol; D009532:Nickel; D006861:Hydrogen Peroxide; D001554:Benzene; C034221:catechol; D010100:Oxygen