Pillar[3]trianglamines: deeper cavity triangular macrocycles for selective hexene isomer separation

by Ding, Y., Alimi, L. O., Du, J., Hua, B., Dey, A., Yu, P., Khashab, N. M.
Year: 2022 DOI: 10.1039/D2SC00207H


Ding, Y.; Alimi, L. O.; Du, J.; Hua, B.; Dey, A.; Yu, P.; Khashab, N. M., Pillar[3]trianglamines: deeper cavity triangular macrocycles for selective hexene isomer separation. Chem. Sci. 2022, 13, 3244-3248


The separation of α-olefins and their corresponding isomers continues to be a big challenge for the chemical industry due to their overlapping physical properties and low relative volatility. Herein, pillar[3]trianglamine (P-TA) macrocycles were synthesized for the molecular-sieving-like separation of 1-hexene (1-He) selectively over its positional isomer trans-3-hexene (trans-3-He) in the vapor and liquid state. This allyl-functionalized macrocycle features a deeper cavity compared to the previously reported trianglamine host molecules. Solid–vapor sorption experiments verified the successful separation of 1-He from an equimolar mixture of 1-He and trans-3-He. Single-crystal structures and powder X-ray diffraction patterns suggest that this selective adsorption arises from the formation of a thermodynamically stable host–guest complex between 1-He and P-TA. A reversible transformation between the nonporous guest-free structure and the guest-containing structure shows that 1-He separation can be carried out over multiple cycles without any loss of performance. Significantly, P-TA can separate 1-He directly from a liquid isomeric mixture and thus P-TA modified silica sieves (SBA-15) showed the ability to selectively separate 1-He when utilized as a stationary phase in column chromatography. This capitalizes on the prospects of employing macrocyclic hosts as molecular recognition units in real-life separations for sustainable and energy-efficient industrial practices.