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Vanadium aminophenolates in catechol oxidation: conformity with Finke's common catalyst hypothesis.
Pasi Salonen1, Risto Savela2, Anssi Peuronen1
1Group of Inorganic Materials Chemistry, Department of Chemistry, University of Turku, FI-20014 Turku, Finland. arileh@utu.fi.
Dalton Transactions (Cambridge, England : 2003)
|May 11, 2021
Summary
Vanadium aminophenolate complexes (V1-V6) were re-evaluated for 3,5-di-tert-butylcatechol oxidation. Contrary to prior studies, these complexes convert to active vanadium catecholate species, challenging their use as direct catechol oxidase mimics.
Area of Science:
- Inorganic Chemistry
- Organometallic Chemistry
- Catalysis
Background:
- Vanadium aminophenolate complexes have been investigated for catechol oxidase-like activity.
- Previous studies suggested complexes V1-V5 catalytically oxidize 3,5-di-tert-butylcatechol (1) to 3,5-di-tert-butyl-1,2-benzoquinone (2).
Purpose of the Study:
- To critically re-evaluate the catalytic behavior of six vanadium aminophenolate complexes (V1-V6) in the aerobic oxidation of 3,5-di-tert-butylcatechol (1).
- To investigate the mechanistic pathways and identify the true active species involved in the oxidation reaction.
Main Methods:
- Aerobic oxidation of 3,5-di-tert-butylcatechol (1) using vanadium complexes V1-V6.
- Mechanistic studies employing Electron Paramagnetic Resonance (EPR), negative mode Electrospray Ionization Mass Spectrometry (ESI-MS), and 51V Nuclear Magnetic Resonance (NMR).
- Product distribution analysis using Gas Chromatography (GC) and column chromatography.
Main Results:
- Complexes V1-V6 produced multiple catechol dioxygenase products, not solely 3,5-di-tert-butyl-1,2-benzoquinone (2).
- Vanadium complexes were found to undergo in situ leaching by H2O2 to form active vanadium catecholate species.
- The identified active species, [V(3,5-DTBC)2(3,5-DTBSQ˙)] and [VO(3,5-DTBC)(3,5-DTBSQ˙)], support the 'common catalyst hypothesis'.
Conclusions:
- Vanadium aminophenolate complexes are susceptible to H2O2-mediated leaching in the presence of strong donating ligands.
- The previously assumed catechol oxidase mimicry of these vanadium complexes is not well-supported.
- The true catalytic activity likely stems from in situ generated vanadium catecholate species.
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