Catalytically-active porous assembly with dynamic pulsating motion for efficient exchange of products and reagents

Abstract

Despite recent advances in the use of porous materials as efficient heterogeneous catalysts which operate through effectively trapping reagents in a well-defined space, continuously uptaking reagents to substitute products in the cavity for efficient product turnover still remains challenging. Here, a porous catalyst is endowed with 'breathing' characteristics by thermal stimulus, which can enable the efficient exchange of reagents and products through reversible stacking from inflated aromatic hexamers to contracted trimeric macrocycles. The contracted super-hydrophobic tubular interior with pyridine environment exhibits catalytic activity towards a nucleophilic aromatic substitution reaction by promoting interactions between concentrated reagents and active sites. Subsequent expansion facilitates the exchange of products and reagents, which ensures the next reaction. The strategy of mesoporous modification with inflatable transition may provide a new insight for construction of dynamic catalysts.

Fig. 1. Molecular structure and thermo-responsive tubular catalyst.

a Molecular structures of 1 and 2. b Schematic representation of thermo-responsive tubular catalyst with inflated transition. Cyan and pink balls stand for R1 and R2 while the combination of cyan and pink balls represents product.

Fig. 2. Structural characterization of tubules 1 and 2.

TEM micrographs of 1 (a) and 2 (b) from aqueous solution (0.01 wt%), scale bar is 5 nm. STEM images of 1 (c) and 2 (d) from aqueous solution (0.01 wt%), scale bar is 50 nm. 2D XRD patterns of 1 (e) and 2 (f) from aqueous solution (0.02 wt%), y-axis: q space [Å⁻¹]. For details, see Supplementary Fig. 4.

Fig. 3. Mutual interaction between reagents and tubules.

a FTIR spectra of 1, 2, R2, 1 with R2, 2 with R2. b Encapsulation efficiency of R1 and product by tubules 1 and 2. c Schematic representation of interaction between R2 and pyridines in trimeric and hexameric macrocycles. Pink balls stand for R2.

Fig. 4. Tubular expansion upon heating.

a FTIR spectra of 1 at 25 and 60 °C. Stained TEM images of 1 dried at 25 °C (b) and 60 °C (c), scale bar is 25 nm. Inset in (b) and (c) is corresponding density profile.

Fig. 5. Exchange of product and R1 for S_NAr reaction.

a Exchange of product and R1 within tubule 1 upon new addition of R1 at 60 °C after reaction. b Repeated cycles of conversion as a function of recycle times. The first recycle was without heating treatment.