Polyoxomolybdates as efficient catalysts for Knoevenagel condensation reaction of benzaldehyde and ethyl cyanoacetate un
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Polyoxomolybdates as efficient catalysts for Knoevenagel condensation reaction of benzaldehyde and ethyl cyanoacetate under mild condition Baijie Xu1, Zhihao liu1, Qiaofei Xu1, Xiao Han1, Xinyi Ma1, Jiawei Wang1, Thirumurthy Kannan1, Pengtao Ma1, Jingping Wang1,*, and Jingyang Niu1,* 1
Henan Key Laboratory of Polyoxometalate Chemistry, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, Henan, People’s Republic of China
Received: 1 September 2020
ABSTRACT
Accepted: 9 November 2020
The development of new heterogeneous catalysts for Knoevenagel condensation reaction is critical for practical applications. Herein, we prepared three organophosphonate-functionalized polyoxomolybdates, Cs2Na9H9[{Co(H2 O)4}(TeMo6O21)2{Co(OOCCH2NCH2PO3)2}3]41H2O (1), Cs2Na8[H6{Co(H2O)4}3 (SeMo6O21)2{Co(OOCCH2NCH2PO3)2}3]31H2O (2) and Cs2Na9H3[H6{Ni(H2 O)4}(SeMo6O21)2{Ni(OOCCH2NCH2PO3)2}3]28H2O (3), which exhibit high catalytic activity for gram-scale Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate. Especially, under the optimal conditions, compound 1 can achieve a satisfactory yield (98%) and show high TON value (1960), which is superior to that of compounds 2 and 3. Notably, the TON value is much higher than that of previously reported catalysts. Such high catalytic performance could be attributed to the co-existence of Lewis acid and Lewis base sites in catalysts. In addition, based on substrates screening and recyclability tests, 1 has exhibited broad catalytic generality and good recyclability.
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Handling Editor: Catalin Croitoru.
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https://doi.org/10.1007/s10853-020-05562-x
J Mater Sci
GRAPHICAL ABSTRACT
Introduction Polyoxometalates (POMs) as a kind of nanosized metal-oxide clusters are typically composed of highvalent early transition metals, such as Mo (VI), W (VI), V (V), Nb (V) and Ta (V) [1–5]. The characteristics and compositions of POMs are strongly tunable using multiple well-established synthetic strategies [6–8]. Besides, POMs have showed splendid potential in many fields [9–15], such as magnetism, electrochemistry, fluorescence, medicine, and especially in catalysis. Particularly, POMs have been widely employed in various catalytic systems for their high activity, selectivity and controllable redox properties [16–18]. As one of the most significant and classic reactions forming C = C bonds [19, 20], Knoevenagel condensation reaction has been widely applied in many fields such as pharmaceuticals [21, 22], fine chemicals [23–25] and perfume [26]. Traditionally, this important reaction, active methylene compounds react with ketones or aldehydes, was carried out in the presence of organic base containing pyrrolidine, piperidine or inorganic base such as KF, K2CO3 and NaHCO3
[27–30], though they come with some obvious weaknesses, including long reaction time, high reaction temperature and environmental pollution [31, 32]. In this
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