Pyridyl-phenylethynylene bis-urea macrocycles: self-assembly and utility as a nanoreactor for the selective photoreaction of isoprene

Abstract

Porous organic crystalline materials were obtained by the self-assembly of pyridyl-phenylethynylene bis-urea macrocycles (1). In contrast to the typical columnar assembly of other bis-urea macrocycles, 1 assembled into interdigitated layers to afford a host with small 1D channels with a pore diameter of ∼4.5 Å. Herein, we discuss the origin between the expected and observed assembly and demonstrate the utility of these activated organic crystals to absorb a guest and maintain crystallinity during the reaction of the encapsulated guest and subsequent product isolation. Isoprene was chosen as a model monomer due to the small channel diameter of 1. The activated crystals were able to absorb isoprene and facilitate a photoinitiated and stereoselective oligomerization to produce trans-1,4-polyisoprene with low dispersity. The products were readily extracted from the crystals and analysis of the microstructure of the oligomer showed 97% trans-1,4 content and a dispersity (Đ) of 1.39. Despite the altered assembly pattern of this bis-urea macrocycle, powder X-ray diffraction studies demonstrated that the crystalline host was remarkably robust and stable throughout the activation, isoprene absorption, photoinduced polymerization, and product recovery processes. Our future investigations are focused on assessing the stability of the isoprene radicals within the host and evaluating the loading and reaction of other monomers.