Dioxovanadium(v) complexes with side chain substituted N-salicylidenehydrazides modelling supramolecular interactions in vanadium haloperoxidases

Mixed‐Ligand Oxidovanadium(V) Complexes with N′‐Salicylidenehydrazides: Synthesis, Structure, and 51V Solid‐State MAS NMR Investigation

“…[40] The trans influence of the oxido group leads to a rather long V-N bond to the nitrogen atom of the 8-hydroxyquinoline coligand (235 pm), and consequently to a displacement of the vanadium atom towards the oxido group out of the tetragonal basal plane by about 30 pm. The observed bond lengths of the amide group of the hydrazone ligand are consistent with its dianionic form, [23,28] whereas for complexes (7) O21-V2-O22 99.59(7) O11-V1-O13 99.02 (7) O21-V2-O23 97.04(7) O11-V1-O15 101.26 (7) O21-V2-O25 99.21(7) O11-V1-N11 98.05 (7) O21-V2-N21 99.95(7) O11-V1-N13 176.51 (7) O21-V2-N23 173.81(7) O12-V1-O13 153.98 (6) O22-V2-O23 155.27(6) O12-V1-O15 103.33 (6) O22-V2-O25 101.34(6) O12-V1-N11 83.83 (6) O22-V2-N21 83.79(6) O12-V1-N13 84.26 (6) O22-V2-N23 85.47(6) O13-V1-O15 91.50 (6) O23-V2-O25 93.89(6) O13-V1-N11 75.09 (6) O23-V2-N21 75.37(6) O13-V1-N13 78.51 (6) O23-V2-N23 79.33(6) O15-V1-N11 158.01 (6) O25-V2-N21 159.03(6) O15-V1-N13 76.46 (6) O25-V2-N23 76.18(6) N11-V1-N13 83.73 (6) N21-V2-N23 84.05 (6) with the coordinated keto form of the ligand the C-O bond is considerably elongated. [22] The hydrogen-bonding interactions induced by the hydroxy group of the side-chain substituted NЈ-salicylidenehydrazide ligand leads to the formation of a chainlike arrangement as depicted in Figure 5.…”

“…The obtained complexes show very good solubility in a broad range of organic solvents like alcohols, DMF, DMSO, chloroform, dichloromethane, and acetonitrile. It should be noted here that attempts to utilize ammonium metavanadate in methanol solution directly as a vanadium(V) precursor did not lead to the desired complexes, but instead afforded a mixture of the corresponding ammonium salt of the cis-dioxidovanadium(V) complexes [15,28] and bis(8-hydroxyquinolinato)methoxyoxidovanadium(V). The formation of an oxidovanadium(V) moiety in the synthesized mixed-ligand complexes is confirmed by their IR spectra, which reveal a strong band at 969 cm -1 for [VO-(salhyhb)(hq)] and 972 cm -1 for [VO(salhyhp)(hq)] and [VO-(salhyhh)(hq)], characteristic of the stretching vibration of the V=O moiety.…”

“…Monitoring this reaction by 51 V NMR spectroscopy shows that 1 equiv. of alkaline base is required for a complete cleavage of the 8-hydroxyquinolinate coligand, with a resonance at -536 ppm for the final cis-dioxidovanadium(V) complex [28] that is stable even in the presence of excess base.…”

“…[25][26][27] A particular feature is the formation of intramolecular hydrogen-bonding interactions with the vanadate moiety, in this case a hydroxy functionalized side chain. [28,29] In the present work, we report on a series of mixed-ligand oxidovanadium(V) complexes containing the ω-hydroxy functionalized NЈ-salicylidenehydrazide ligand system together with the electrochemically interesting 8-hydroxyquinoline as a coligand. In addition to their electrochemical properties we also investigated these compounds by 51 V solid-state NMR spectroscopy.…”

Vanadium(V) Oxoperoxo Complexes with Side Chain SubstitutedN‐Salicylidenehydrazides: Modeling Supramolecular Interactions inVanadium Haloperoxidases

“…[21] This crucial role could neither be confirmed by site-directed mutagenesis studies, [22] nor by catalytic studies of model systems containing a relevant hydroxy side chain. [17] However, in mutagenesis studies a significant decrease in the enzyme activity could be observed for the chlorination and bromination reactions to about 4 and 20 %, respectively. [22] This indicates that the serine residue, although not crucial, plays an important role in affecting the reactivity of the active site.…”