Abstract：
Multifunctional heterogeneous catalysts are an effective strategy to drive chemical cascades, with attendant time, resource and cost efficiencies by eliminating unit operations arising in normal multistep processes. Despite advances in the design of such catalysts, the fabrication of proximate, chemically antagonistic active sites remains a challenge for inorganic materials science. Hydrogen-bonded organocatalysts offer new opportunities for the molecular level design of multifunctional structures capable of stabilising antagonistic active sites. We report the catalytic application of a charge-assisted, hydrogen-bonded crystalline material, bis(melaminium)adipate (BMA), synthesised from melamine and adipic acid, which possesses proximate acid-base sites. BMA exhibits high activity for the cascade deacetalisation-Knoevenagel condensation of dimethyl acetals to form benzylidenemalononitriles under mild conditions in water; BMA is amenable to large-scale manufacture and recycling with minimal deactivation. Computational modelling of the melaminium cation in protonated BMA explains the observed catalytic reactivity, and identifies the first demethoxylation step as rate-limiting, in good agreement with time-dependent 1H NMR and kinetic experiments. A broad substrate scope for the cascade transformation of aromatic dimethyl acetals is demonstrated.
摘要：
多功能多相催化剂是驱动化学级联的有效策略，随着时间的推移，通过消除在正常的多步骤过程中产生的单元操作来提高资源和成本效率。尽管这种催化剂的设计取得了进展，近似的制造，化学拮抗活性位点仍然是无机材料科学的挑战。氢键有机催化剂为能够稳定拮抗活性位点的多功能结构的分子水平设计提供了新的机会。我们报告了电荷辅助的催化应用，氢键晶体材料，己二酸双（三聚氰胺）（BMA），由三聚氰胺和己二酸合成，具有邻近的酸碱位点。在温和的水中条件下，BMA对二甲基缩醛的级联脱缩醛-Knoevenagel缩合反应具有很高的活性，可形成亚苄基甲醛腈；BMA适合大规模生产和再循环，而失活最少。质子化BMA中melaminum阳离子的计算模型解释了观察到的催化活性，并将第一个去甲氧基化步骤确定为限速步骤，与时间相关的1HNMR和动力学实验非常吻合。证明了芳族二甲基缩醛级联转化的广泛底物范围。
