Abstract
We demonstrated for the first time that [Nb10O28]6− exhibited base catalytic activity for aldol-type condensation reactions including Knoevenagel and Claisen–Schmidt condensation reactions.
Highlights
A polyoxometalate (POM),1 [MxOy]nÀ, is an anionic metal-oxide cluster that consists of a given number of [MO6] octahedral units by sharing edges or corners
Density functional theory calculations showed that the oxygen atoms in the cluster are highly negatively charged and suggested the possibility that the cluster can act as a base catalyst
We demonstrated for the first time that [Nb10O28]6À exhibits base catalytic activity for aldol-type condensation reactions including Knoevenagel and Claisen–Schmidt condensation reactions
Summary
A polyoxometalate (POM),1 [MxOy]nÀ, is an anionic metal-oxide cluster that consists of a given number of [MO6] octahedral units by sharing edges or corners. We focused on [Nb10O28]6À rather than [Nb6O19]8À the latter has more negative Àn/y value This is because the crystal structure of tetramethylammonium (TMA) salt, that can be dispersed in organic solvent, have been reported only for [Nb10O28]6À.12. In this communication, we theoretically compared negative charges of oxygen atoms of [Nb10O28]6À with those of POWs. we applied (TMA)6[Nb10O28]$6H2O as homogeneous catalyst for aldol-type condensation reactions such as Knoevenagel and Claisen–Schmidt condensation reactions and revealed for the rst time that it acted as a Brønsted base catalyst whose strength is comparable to superbases. This result will open up a new possibility of application of PONbs since their catalytic application has been limited to electrocatalysts[13] and photocatalysts so far.[14,15,16,17]
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