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. 2024 Mar 11;9(12):14233-14240.
doi: 10.1021/acsomega.3c09911. eCollection 2024 Mar 26.

Confinement Effect in Metal-Organic Framework Cu3(BTC)2 for Enhancing Shape Selectivity of Radical Difunctionalization of Alkenes

Mochen Li  1 , Zhi Feng  1 , Chunying Duan  1   2 , Tiexin Zhang  1 , Yusheng Shi  3
Affiliations

Confinement Effect in Metal-Organic Framework Cu3(BTC)2 for Enhancing Shape Selectivity of Radical Difunctionalization of Alkenes

Mochen Li et al. ACS Omega. .

Abstract

The radical difunctionalization of alkenes plays a vital role in pharmacy, but the conventional homogeneous catalytic systems are challenging in selectivity and sustainability to afford the target molecules. Herein, the famous readily available metal-organic framework (MOF), Cu3(BTC)2, has been applied to cyano-trifluoromethylation of alkenes as a high-performance and recyclable heterogeneous catalyst, which possesses copper(II) active sites residing in funnel-like cavities. Under mild conditions, styrene derivatives and various unactivated olefins could be smoothly transformed into the corresponding cyano-trifluoromethylation products. Moreover, the transformation brought about by the active copper center in confined environments achieved regio- and shape selectivity. To understand the enhanced selectivity, the activation manner of the MOF catalyst was studied with control catalytic experiments such as FT-IR and UV-vis absorption spectroscopy of substrate-incorporated Cu3(BTC)2, which elucidated that the catalyst underwent a radical transformation with the intermediates confined in the MOF cavity, and the confinement effect endowed the method with pronounced selectivities.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Schematic illustration of designing shape- and regioselective cyano-trifluoromethylation of alkenes by MOF Cu3(BTC)2 endowed by Cu(II) sites in funnel-like cavities.
Figure 2
Figure 2
Correlation of catalyst activity with the steric environment around the alkene moieties. The dashed frames mark the surrounding steric moieties.
Figure 3
Figure 3
(a) FT-IR spectra of Togni reagent II, thermal-activated Cu3(BTC)2, and Togni reagent@Cu3(BTC)2. (b) UV–vis absorption spectra of thermally activated Cu3(BTC)2 and Togni reagent@Cu3(BTC)2. (c) Illustration of the origin of regio- and shape selectivities. (d) Time-coursed reaction kinetics and catalyst hot-filtration experiment. (e) Catalyst recycle experiment. (f) Powder X-ray diffractogram (PXRD) spectra of simulated, as-synthesized, and recovered Cu3(BTC)2 samples. (g) Comparative FT-IR spectra of as-synthesized and recovered Cu3(BTC)2. (h) Interference experiments in the presence of additives. (i) HRMS spectrum of the TEMPO-trapping experiment.
Scheme 1
Scheme 1. Control Experiments
(1) Ring-opening reaction of (−)-β-Pinene 1q. (2) Radical-clock reaction of 1r. (3) BHT as hydrogen donor in trifluoromethylation–cyclization reaction of 1r (isolated yields).
Scheme 2
Scheme 2. Proposed Mechanism of Cyano-Trifluoromethylation of Alkene Catalyzed by Cu3(BTC)2
Scheme 3
Scheme 3. Cu3(BTC)2 Promoted Azido-Trifluoromethylation (Isolated Yields)
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