Stable, crystalline, porous, covalent organic frameworks as a platform for chiral organocatalysts

Abstract

The periodic layers and ordered nanochannels of covalent organic frameworks (COFs) make these materials viable open catalytic nanoreactors, but their low stability has precluded their practical implementation. Here we report the synthesis of a crystalline porous COF that is stable against water, strong acids and strong bases, and we demonstrate its utility as a material platform for structural design and functional development. We endowed a crystalline and porous imine-based COF with stability by incorporating methoxy groups into its pore walls to reinforce interlayer interactions. We subsequently converted the resulting achiral material into two distinct chiral organocatalysts, with the high crystallinity and porosity retained, by appending chiral centres and catalytically active sites on its channel walls. The COFs thus prepared combine catalytic activity, enantioselectivity and recyclability, which are attractive in heterogeneous organocatalysis, and were shown to promote asymmetric C-C bond formation in water under ambient conditions.

Photoactive and Conducting Covalent Organic Frameworks

“…By installing electron donating methoxy groups on the linear arene subunits a reduction of the imine bond polarization was achieved, a COF with enhanced stability and crystallinity in comparison to its nonmodified COF homologue was reported. [17] Introducing intramolecular hydrogen bonding was explored by Banerjee and co-workers as a method to stabilize iminebased COFs by induced planarization of the 2D COF sheets. [18] Adv.…”

Tuning the adsorption and fluorescence properties of aminal‐linked porous organic polymers through N‐heterocyclic group decoration

“…[15][16][17][18] It has been revealed that the properties of polymer depend mainly on the polymer architecture as well as the intrinsic properties of synthons. For example, the polymers comprising of larger conjugated system is of benefit to the adsorption of H 2 19,20 as well as the fluorescent detection of Nitro-benzene derivatives, while the polymers with large N content usually exhibits promoted adsorption affinity toward CO 2 .…”

Asymmetric Hydrogenation of β-Keto Esters Catalyzed by Ruthenium Species Supported on Porous Organic Polymer

“…[35] Furthermore, Jiang and coworkers have reported the metal-free heterogeneous organocatalysis of chiral COFs materials which display excellent activity, enantio-selectivity and recyclability. [36,37] Among chiral functional groups employed in asymmetric catalysts, so-called "privileged" chiral ligands such as 1-(2-hydroxynaphthalen-1-yl)naphthalen-2-ol (BINOL), 2,2'-bis(diphenylphosphino)-1,1'-binaphthalene (BINAP), salen, bisoxazoline and TADDOLate, have been proven to be highly efficient to a wide range of different reactions.…”