In:
Angewandte Chemie, Wiley, Vol. 136, No. 17 ( 2024-04-22)
Abstract:
Here, doubly protonated Lindqvist‐type niobium oxide cluster [H 2 (Nb 6 O 19 )] 6– , fabricated by microwave‐assisted hydrothermal synthesis, exhibited superbase catalysis for Knoevenagel and crossed aldol condensation reactions accompanied by activating C−H bond with p K a 〉 26 and proton abstraction from a base indicator with p K a =26.5. Surprisingly, [H 2 (Nb 6 O 19 )] 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 NbO 6 units in [H 2 (Nb 6 O 19 )] 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.
Type of Medium:
Online Resource
ISSN:
0044-8249
,
1521-3757
DOI:
10.1002/ange.v136.17
DOI:
10.1002/ange.202401526
Language:
English
Publisher:
Wiley
Publication Date:
2024
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