Abstract
Mn and Fe BPMEN complexes showed excellent reactivity in catalytic oxidation with an excess of co-reagent (CH3COOH). In the straight line of a cleaner catalytic system, volatile acetic acid was replaced by SiO2 (nano)particles with two different sizes to which pending carboxylic functions were added (SiO2@COOH). The SiO2@COOH beads were obtained by the functionalization of SiO2 with pending nitrile functions (SiO2@CN) followed by CN hydrolysis. All complexes and silica beads were characterized by NMR, infrared, DLS, TEM, X-ray diffraction. The replacement of CH3COOH by SiO2@COOH (100 times less on molar ratio) has been evaluated for (ep)oxidation on several substrates (cyclooctene, cyclohexene, cyclohexanol) and discussed in terms of activity and green metrics.
Highlights
The synthesis of epoxides/ketones is an interesting research field from the fundamental to the applicative point of view in organic synthesis or catalysis
In order to study the influence of the counter anion during the catalysis and more with the use of the silica beads, three MnII metal complexes with different anions were synthetized according to Figure 1. (L)MnCl2 was obtained in 65% yield by reaction between BPMEN (L) and MnCl2·4H2O in acetonitrile [56]
The study showed lower activity with the silica beads in the case of cyclooctene and cyclohexene oxidation with manganese complexes and selectivity seemed to be linked to the nature of the ion of the complex
Summary
The synthesis of epoxides/ketones is an interesting research field from the fundamental to the applicative point of view in organic synthesis or catalysis Those organic compounds can be obtained using very simple organic oxidants (but quite tedious in the post-treatment procedure) like meta-chloroperbenzoic acid (m-CPBA) [1,2], NaIO4 [3], RCO3H [4,5,6]. Silica was employed previously for different uses, especially to graft, in a covalent way, polydentate ligands and related complexes for catalyzed reactions, or to trap heavy metals for depollution concerns. Those strategies used mainly mesoporous compounds [47,48,49,50,51] but rarely nonporous silica beads. Those systems showed interesting results in the oxidation reaction on several substrates [52,53]
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