The Ionic Organic Cage: An Effective and Recyclable Testbed for Catalytic CO2 Transformation

Wenlong Wang,Yanping Huo,Lifeng Cui,Jutao Jin,Yuanyou Mao

doi:10.3390/catal11030358

Wenlong Wang, Yanping Huo + Show 3 more

Open Access

https://doi.org/10.3390/catal11030358

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Abstract

Porous organic cages (POC) are a class of relatively new molecular porous materials, whose concept was raised in 2009 by Cooper’s group and has rarely been directly used in the area of organic catalysis. In this contribution, a novel ionic quasi-porous organic cage (denoted as Iq-POC), a quaternary phosphonium salt, was easily synthesized through dynamic covalent chemistry and a subsequent nucleophilic addition reaction. Iq-POC was applied as an effective nucleophilic catalyst for the cycloaddition reaction of CO2 and epoxides. Owing to the combined effect of the relatively large molecular weight (compared with PPh3+I−) and the strong polarity of Iq-POC, the molecular catalyst Iq-POC displayed favorable heterogeneous nature (i.e., insolubility) in this catalytic system. Therefore, the Iq-POC catalyst could be easily separated and recycled by simple centrifugation method, and the catalyst could be reused five times without obvious loss of activity. The molecular weight augmentation route in this study (from PPh3+I− to Iq-POC) provided us a “cage strategy” of designing separable and recyclable molecular catalysts.

Highlights

In 2009, Cooper and co-workers discovered a new type of 3D discrete molecular cages with a central cavity and molecule accessible windows, and named them porous organic cages (POC) [1]
When thinking at a higher level about the assembly, scientists found that POC materials are assembled by two organic synthons through dynamic covalent chemistry (DCC) [5], which means POC materials are constructed by reversible covalent bonds only, and this is the main characteristic that distinguishes them from other cage materials
Owing to the amplified cage structure, the nucleophilic cage Iq-POC is insoluble in propylene oxide and propylene carbonate; after the reaction, Iq-POC could be separated from the reaction system through filtration or centrifugation

Summary

Introduction

In 2009, Cooper and co-workers discovered a new type of 3D discrete molecular cages with a central cavity and molecule accessible windows, and named them porous organic cages (POC) [1] Research in this field has been on the rise in the last decade [2,3,4,5,6,7,8,9,10,11], with imine condensation [12,13,14,15,16,17,18] and boronic esters formation [19,20,21,22,23,24,25,26] being the two main strategies for constructing POC materials. Almost all the homogeneous nucleophile catalysts are hard to recover and reuse; from the viewpoint of green catalysis, it is necessary to develop a recyclable nucleophile catalyst [81] In this contribution, a novel quasiionic porous organic cage (Iq-POC), a quaternary phosphonium salt, was synthesized and utilized as a recyclable nucleophile catalyst (Figure 1a). N2 adsorption isotherm revealed the cage was nonporous

Synthesis of the Cage 3

Synthesis of Iq-POC

General Procedure of Catalytic Reactions

Findings

Conclusions