A Robust Porous Quinoline Cage: Transformation of a [4+6] Salicylimine Cage by Povarov Cyclization

Abstract

Porous shape-persistent organic cages have become the object of interest in recent years because they are soluble and thus processable from solution. A variety of cages can be achieved by applying dynamic covalent chemistry (DCC), but they are less chemically stable. Here the transformation of a salicylimine cage into a quinoline cage by a twelve-fold Povarov reaction as the key step is described. Besides the chemical stability of the cage over a broad pH regime, it shows a unique absorption and emission depending on acid concentration. Furthermore, thin films for the vapor detection of acids were investigated, showing color switches from pale-yellow to red, and characteristic emission profiles.

Dynamic Nucleophilic Aromatic Substitution of Tetrazines

“…To the best of our knowledge, there are only a couple of precedents of such post‐stabilization by Diels–Alder reaction and in both cases, only for DCC products based on imines. [ 112 , 113 ]…”

Soluble Congeners of Prior Insoluble Shape‐Persistent Imine Cages

“…[1][2][3][4][5][6][7][8][9][10] In addition to the shape-persistency and thus the presence of an intrinsic pore or cavity, these molecular compounds can be seen as processable porous units, if soluble enough. This unique combination of porous cage properties has been used to decorate surfaces of quartz crystal microbalances, [11,12] making cage-containing membranes, [13,14] coating columns with cages for gas chromatographic purposes, [15,16] using cage-films for sensing applications, [17] or generating porous liquids. [18,19] Nowadays, shape-persistent organic cages are mainly synthesized by using reversible condensation reactions, such as by multiple imine bond formation or the generation of boronic esters from the corresponding diols and boronic acids.…”

“…[ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ] In addition to the shape‐persistency and thus the presence of an intrinsic pore or cavity, these molecular compounds can be seen as processable porous units, if soluble enough. This unique combination of porous cage properties has been used to decorate surfaces of quartz crystal microbalances,[ 11 , 12 ] making cage‐containing membranes,[ 13 , 14 ] coating columns with cages for gas chromatographic purposes,[ 15 , 16 ] using cage‐films for sensing applications, [17] or generating porous liquids. [ 18 , 19 ]…”

Hierarchically Porous Organic Cages

“…Porous organic cages are emerging microporous materials that have cavities in discrete individual molecules. They are currently intensively explored for applications including molecular recognition, [6a,b] catalysis [6c–g] and gas storage and separation [6h–l] . One of their key features is their molecular solubility, which in turn enables supramolecular self‐assembly to engineer long‐range ordered hierarchical structures, driven by noncovalent forces, such as van der Waals and dipole–dipole interactions, etc [7] .…”