da Camara Bryce, Woods Connor Z, Sharma Komal, Wu Hoi-Ting, Farooqi Naira S, Chen Changwei, Julian Ryan R, Vander Griend Douglas A, Hooley Richard J
Department of Chemistry and the UCR Center for Catalysis, University of California - Riverside, Riverside, CA 92521, USA.
Department of Chemistry & Biochemistry, Calvin University, Grand Rapids, MI 49546, USA.
Chemistry. 2023 Nov 13;29(63):e202302499. doi: 10.1002/chem.202302499. Epub 2023 Sep 29.
Spacious M L tetrahedra can act as catalytic inhibitors for base-mediated reactions. Upon adding only 5 % of a self-assembled Fe L cage complex, the conversion of the conjugate addition between ethylcyanoacetate and β-nitrostyrene catalyzed by proton sponge can be reduced from 83 % after 75 mins at ambient temperature to <1 % under identical conditions. The mechanism of the catalytic inhibition is unusual: the octacationic Fe L cage increases the acidity of exogenous water in the acetonitrile reaction solvent by favorably binding the conjugate acid of the basic catalyst. The inhibition only occurs for Fe L hosts with spacious internal cavities: minimal inhibition is seen with smaller tetrahedra or Fe L helicates. The surprising tendency of the cationic cage to preferentially bind protonated, cationic ammonium guests is quantified via the comprehensive modeling of spectrophotometric titration datasets.
宽敞的M L四面体可作为碱介导反应的催化抑制剂。仅添加5%的自组装铁L笼配合物，质子海绵催化的氰基乙酸乙酯与β-硝基苯乙烯之间的共轭加成反应在室温下75分钟后的转化率可从83%降至相同条件下的<1%。催化抑制机制不同寻常：八阳离子铁L笼通过与碱性催化剂的共轭酸形成有利结合，提高了乙腈反应溶剂中外源水的酸度。抑制作用仅发生在具有宽敞内腔的铁L主体上：较小的四面体或铁L螺旋体的抑制作用最小。通过对分光光度滴定数据集的全面建模，定量了阳离子笼优先结合质子化阳离子铵客体的惊人趋势。
