Imine‐based covalent organic frameworks (COFs) are a widely studied class of functional, crystalline, and porous nanostructures which combine a relatively facile crystallization with tuneable compositions and porosities. However, the imine linkage constitutes an intrinsic limitation due to its reduced stability in harsh chemical conditions and its unsuitability for in‐plane π‐conjugation in COFs. Urgent solutions are therefore required in order to exploit the full potential of these materials, thereby enabling their technological application in electronics, sensing, and energy storage devices. In this context, the advent of a new generation of linkages derived from the chemical conversion and locking of the imine bond represents a cornerstone for the synthesis of new COFs. A marked increase in the framework robustness is in fact often combined with the incorporation of novel functionalities including, for some of these reactions, an extension of the in‐plane π‐conjugation. This Minireview describes the most enlightening examples of one‐pot reactions and post‐synthetic modifications towards the chemical locking of the imine bond in COFs.

The development of efficient homogeneous catalysts for the synthesis of functionalized polyolefins is a challenging topic. Palladium(II) complexes with -diimine ligands having a phenanthrene skeleton and 2,6-disubstituted aryl rings (Ar-BIP) were synthesized, characterized and tested as precatalysts in the copolymerization of ethylene with methyl acrylate. The direct comparison with analogous complexes having the corresponding diimines with an acenaphthene skeleton (Ar-BIAN) was performed. X-ray characterization in solid state and NMR analysis in solution of both neutral, [Pd(Ar-BIP)(CH 3)Cl], and monocationic [Pd(Ar-BIP)(CH 3)(NCCH 3)][PF 6 ] complexes, indicate that the Ar-BIP ligands have a higher Lewis basicity and are more strongly coordinated to the metal center than the Ar-BIAN counterparts. Therefore, the Pd-(Ar-BIP) cationic complexes can be regarded as electronrich metal cations. In addition, they create a higher steric congestion around palladium than Ar-BIAN, regardless of the substituents on the aryl rings. The monocationic species generate active catalysts for the ethylene/methyl acrylate copolymerization leading to copolymers with M n values up to 37000 and a content of polar monomer of 5.3 mol %. The detailed study of the catalytic behavior points out that Pd-(Ar-BIP) catalysts show a good affinity for the polar monomer, a good thermal stability and favor the cleavage of the catalyst resting state, leading to copolymer with Mw values higher than that of the macromolecules produced with the corresponding Pd-(Ar-BIAN) under the same reaction conditions. NMR characterization of the produced copolymers points out that the polar monomer is inserted both at the end of the branches and into the main chain, with a more selective enchainment than that achieved when the copolymerization is carried out in dichloromethane. In situ NMR investigations allowed us to detect relevant intermediates of the catalytic cycle and shed light on the nature of possible deactivation species.

Imine‐based covalent organic frameworks (COFs) are a widely studied class of functional, crystalline, and porous nanostructures which combine a relatively facile crystallization with tuneable compositions and porosities. However, the imine linkage constitutes an intrinsic limitation due to its reduced stability in harsh chemical conditions and its unsuitability for in‐plane π‐conjugation in COFs. Urgent solutions are therefore required in order to exploit the full potential of these materials, thereby enabling their technological application in electronics, sensing, and energy storage devices. In this context, the advent of a new generation of linkages derived from the chemical conversion and locking of the imine bond represents a cornerstone for the synthesis of new COFs. A marked increase in the framework robustness is in fact often combined with the incorporation of novel functionalities including, for some of these reactions, an extension of the in‐plane π‐conjugation. This Minireview describes the most enlightening examples of one‐pot reactions and post‐synthetic modifications towards the chemical locking of the imine bond in COFs.