Summary

使用气性金属-有机框架 (MoF) 开发异构异构选择性催化剂

Published: January 17, 2020
doi:

Summary

在这里,我们提出了一个协议,通过比较化学计量和催化碳基-ene反应,以找出反应是否发生在金属-有机框架的内表面或外表面,金属-有机框架的活性现场验证。

Abstract

基底尺寸由反应部位手性环境的孔径和均匀性进行区分,是金属-有机框架(MOF)中基于的催化剂在抗选择性催化反应中验证反应位点的重要问题系统。因此,有必要用一种验证基于MOF的催化剂反应位的方法来研究这个问题。通过将基板大小与两种不同类型的碳基-ene反应的的反应速率与两种 MoF 进行比较,实现了基底尺寸按孔径尺寸进行区分。MOF催化剂用于比较两种反应类型(锌介导的化学计量和Ti催化碳基-ene反应)在两种不同介质中的性能。采用该方法,观察到整个MOF晶体参与了反应,当反应是气算计时,晶体孔的内部在施加手性控制方面发挥了重要作用。MOF催化剂手性环境的均质性,通过锌介导的化学计量反应系统中使用的粒子的尺寸控制方法确定。为催化反应提出的方案表明,无论基质大小如何,反应主要发生在催化剂表面,揭示了MOF异构催化剂中的实际反应位点。该方法用于MOF催化剂的反应现场验证,为开发异构异构选择性MOF催化剂提出了各种考虑。

Introduction

MoFs 被认为是化学反应的有用异构催化剂。有许多不同的报告使用MoF用于抗选择性催化1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17 1819.不过,目前尚不清楚这些反应是发生在MoFs的内表面还是外表面。最近的研究提出了关于利用可用表面和减少扩散20,21,22,23的问题。一个更引人注目的问题是,手性环境随MOF晶体中每个腔的位置而变化。手性环境的这种异质性意味着反应产物的立体选择性取决于反应位24。因此,设计一个高效的抗选择性催化剂需要确定反应发生的位置。为此,必须确保反应仅在内表面或仅在 MOF 的外表面发生,同时保持内部完好无损。MoF的多孔结构及其含有手性环境活性位点的较大表面积可用于内选性催化。因此,MoFs是固体支持异构催化剂25的极佳替代品。如果MoF内部没有反应,则需要重新考虑使用MoF作为异构催化剂。反应部位的位置很重要,以及腔的大小。在多孔材料中,型腔的大小根据基板的大小决定基板的大小。有一些关于基于MOF的催化剂的报告,它忽视型腔尺寸问题25。许多基于MOF的催化剂将笨重的催化种类(例如,Ti(O-i Pr)4)引入到原来的框架结构3,8,13。在原始框架结构中采用笨重的催化品种时,腔体尺寸发生变化。笨重的催化种类导致的腔体尺寸减小,使得基材无法完全扩散到MoFs中。因此,在这些情况下,需要考虑按 MoF 的空腔大小对基板大小进行区分。MOF的催化反应往往难以支持MOF腔内发生反应的证据。一些研究表明,比MOF腔体更大的基板很容易转化为预期产品,这似乎是矛盾8,13。这些结果可以解释为基板的功能组与启动催化反应的催化位点之间的接触。在这种情况下,无需基板扩散到 MoF;反应发生在MOF晶体26的表面,腔体大小不直接参与基材根据其尺寸的区分。

为了确定MoFs的反应部位,选择了一种已知的刘易斯酸促进碳基-ene反应2。以3-甲基甲酸酯及其同系物为基质,研究了四种类型的苯丙基-烯反应(图1)。此前报道的反应分为两类:使用Zn试剂的化学计量反应和使用Ti试剂27的催化反应。最小基质的反应需要锌/KUMOF-1(KUMOF + 韩国大学金属-有机框架);据报道,这种反应发生在晶体27内部。该方法使用了两种MoF,即用于化学计量反应的Zn/KUMOF-1和用于催化反应的Ti/KUMOF-1。由于这两种MoF的不同反应机制,反应速率与基板大小的比较是可能的2,28,29。颗粒大小对碳基-ene反应的影响与Zn/KUMOF-127表明,如前一份报告所示,外表面的手性环境不同于MOF晶体24的内侧。本文演示了一种通过比较三种基材与两类催化剂的反应和颗粒大小效应的方法,如上文27所述。

Protocol

1. 三种尺寸的 (S) -KUMOF-1 晶体的制备 注:每一步都遵循前一份报告2、24、27的实验部分和补充资料。三种不同尺寸的(S) -KUMOF-1:大 (S) -KUMOF-1-(L), 中等 (S) -KUMOF-1-(M) 和小(S)-KUMOF-1-(S) 粒径 >100 μm, >20 ?…

Representative Results

使用锌试剂的苯基-ene反应是化学计量的,因为甲氧基和碳基组与金属结合亲和力的差异(图2)。因此,基板在反应部位被转换成产品并保留在那里。如协议第4节所述,通过拆除晶体获得所需的产品。锌/(S)-KUMOF-1(表1)对基材的异构异构化碳基-ene反应结果表明,最小基质(1a)可以在晶体内扩散,以高收率(92%)转化为产物?…

Discussion

在合成 (S) –KUMOF-1后, 一些小瓶中的晶体似乎是粉末状的, 不适合用于催化.因此, 需要选择适当的晶体 (S) –KUMOF-1.S) –KUMOF-1的收率仅使用成功合成的小瓶计算。当从溶剂中抽离时, (S) –KUMOF-1拆除.因此,晶体应始终保持湿润。因此, 称称完整 (S) –KUMOF-1晶体浸入溶剂中是很困难的.(

Declarações

The authors have nothing to disclose.

Acknowledgements

这项工作得到了韩国国家研究基金会(NRF)基础科学研究计划NRF-2019R1A2C4070584和由韩国政府资助的NRF-2016R1A5A1009405科学研究中心的支持。S. Kim 获得 NRF 全球博士奖学金 (NRF-2018H1A2A1062013) 的支持。

Materials

Acetone Daejung 1009-4110
Analytical Balance Sartorius CP224S
Copper(II) nitrate trihydrate Sigma Aldrich 61194
Dichloromethane Daejung 3030-4465
Dimethyl zinc Acros 377241000
Ethyl acetate Daejung 4016-4410
Filter paper Whatman WF1-0900
Methanol Daejung 5558-4410
Microwave synthesizer CEM Discover SP
Microwave synthesizer 10 mL Vessel Accessory Kit CEM 909050
N,N-Diethylformamide TCI D0506
N,N-Dimethylaniline TCI D0665
n-Hexane Daejung 4081-4410
Normject All plastic syringe 5 mL luer tip 100/pk Normject A5
Pasteur Pipette 150 mm Hilgenberg HG.3150101
PTFE tape KDY TP-75
Rotary Evaporator Eyela 243239
Shaker DAIHAN Scientific DH.WSO04010
Silica gel 60 (230-400 mesh) Merck 109385
Synthetic Oven Eyela NDO-600ND
Titanium isopropoxide Sigma Aldrich 87560
Vial (20 mL) SamooKurex SCV2660
Vial (5 mL) SamooKurex SCV1545

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Citar este artigo
Han, J., Kim, S., Lee, M. S., Kim, M., Jeong, N. Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs). J. Vis. Exp. (155), e60624, doi:10.3791/60624 (2020).

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