Oxidovanadium ( V ) amine bisphenolates as epoxidation , sulfoxidation and catechol oxidation catalysts

Air-stable oxidovanadium(V) complexes with tetradentate amine bisphenolate ligands were made by the reaction of VOSO4·xH2O and ligand precursors in MeOH solutions. Isolated compounds were studied as catechol oxidase models as well as catalysts for epoxidation and sulfoxidation reactions. All compounds can catalyse such oxidation reactions without notable structure-activity correlations. The V NMR studies indicate that the complexes turn to the number of different species during the catalytic experiments.

Please cite this article as: Pasi Salonen, Anssi Peuronen, Ari Lehtonen , Oxidovanadium(V) amine bisphenolates as epoxidation, sulfoxidation and catechol oxidation catalysts. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Inoche(2017), doi:10.1016/ j.inoche.2017. 10.017 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A C C E P T E D M A N U S C R I P T
3 Oxidovanadium(V) complexes can be used as catalysts for a number of organic oxidation reactions. [1][2][3] Moreover, they are generally considered as model compounds for vanadium-based oxidative enzymes. [4] Tetradentate amine bisphenols are a versatile group of organic ligands as they can form stable complexes with practically all transition metals. [5] Accordingly, a number of oxidovanadium(V) amino bisphenolates are prepared [6][7][8] and used as catalysts for organic oxidation reactions, e.g. the oxidation of catechol to o-benzoquinone, [9] oxidation of dopamine, [10] oxidation of alcohols, [11] oxidation of aromatic hydrocarbons [12], sulfoxidations [13] and coupling CO 2 with epoxides [14]. In some cases, the vanadium compounds are reported to be hydrolytically unstable and possibly decompose under turn-over conditions. [6,9,12] In the present study, we used four oxidovanadium complexes with tetrapodal  [7,13,15] Electronic absorption spectra of complexes 1a 1 In a typical reaction procedure 1.0 mmol of both the free ligands (H 2 L Me or H 2 L tBu ) and VOSO 4 • 5 H 2 O were added in 10 ml of AR-grade MeOH at room temperature, whereupon dark solutions formed. To these solutions was then added 2.1 equivalents of triethyl amine and the solutions were stirred and heated at reflux for three hours. Subsequently the reaction mixtures were allowed to slowly cool to room temperature before they were left to stand at -20°C. In a few days dark to black crystals had formed and they were separated and washed with ice-cold methanol to obtain complexes in 50 -70 % yields. See Supplementary material for the spectroscopic data for 1a and 1b.     3 In a typical experiment, ca. 2 mg of a catalyst precursor and 35 mg of norbornene were dissolved in 0.6 ml of CDCl 3 and 90 µl of tert-BuOOH was added (80-% in water). The reaction was followed by 1 H NMR at 50 °C for 2 hours. In the reaction, the alkene multiplet at 6.0 ppm was turned to the epoxide multiplet at 3.1 ppm. A C C E P T E D M A N U S C R I P T 9

Graphical abstract
Oxidovanadium(V) complexes with tetradentate amine bisphenols catalyse epoxidation and sulfoxidation reactions. They also act as models for catechol oxidase.

ACCEPTED MANUSCRIPT
A C C E P T E D M A N U S C R I P T 10 Highlights  Air-stable oxidovanadium(V) complexes with tetradentate amine bisphenolate ligands were.
 All compounds can act as catechol oxidase models as well as catalysts for epoxidation and sulfoxidation.
 By 51 V NMR, the complexes turn to the number of different species during the catalytic experiments.