Water‐Tolerant Superbase Polyoxometalate [H2(Nb6O19)]6− for Homogeneous Catalysis

Author:

Kikkawa Soichi12ORCID,Fujiki Yu1,Chudatemiya Vorakit1ORCID,Nagakari Hiroki1,Shibusawa Kazuki1,Hirayama Jun12,Nakatani Naoki1ORCID,Yamazoe Seiji123ORCID

Affiliation:

1. Department of Chemistry Graduate School of Science, Tokyo Metropolitan University 1-1 Minami-Osawa, Hachioji Tokyo 192−0397 Japan

2. Elements Strategy Initiative for Catalysts & Batteries (ESICB) Kyoto University 1-30 Goryo-Ohara, Nishikyo-ku, Kyoto, 615−8245 Japan

3. Precursory Research for Embryonic Science and Technology (PRESTO) Japan Science and Technology Agency (JST) 4-1-8, Honcho, Kawaguchi Saitama 332-0012 Japan

Abstract

AbstractHere, 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.

Funder

Yazaki Memorial Foundation for Science and Technology

Publisher

Wiley

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