Water-Tolerant Superbase Polyoxometalate [H2(Nb6O19)]6- for Homogeneous Catalysis.
Angew Chem Int Ed Engl
; 63(17): e202401526, 2024 Apr 22.
Article
em En
| MEDLINE
| ID: mdl-38388816
ABSTRACT
Here, doubly protonated Lindqvist-type niobium oxide cluster [H2(Nb6O19)]6-, fabricated by microwave-assisted hydrothermal synthesis, exhibited superbase catalysis for Knoevenagel and crossed aldol condensation reactions accompanied by activating C-H bond with pKa >26 and proton abstraction from a base indicator with pKa=26.5. Surprisingly, [H2(Nb6O19)]6- exhibited water-tolerant superbase properties for Knoevenagel and crossed aldol condensation reactions in the presence of water, although it is well known that the strong basicity of metal oxides and organic superbase is typically lost by the adsorption of water. Density functional theory calculation revealed that the basic surface oxygens that share the corner of NbO6 units in [H2(Nb6O19)]8- maintained the negative charges even after proton adsorption. This proton capacity and the presence of un-protonated basic sites led to the water tolerance of the superbase catalysis.
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1
Coleções:
01-internacional
Base de dados:
MEDLINE
Idioma:
En
Revista:
Angew Chem Int Ed Engl
Ano de publicação:
2024
Tipo de documento:
Article
País de afiliação:
Japão