Benzene Ring Knitting Achieved by Ambient‐Temperature Dehalogenation via Mechanochemical Ullmann‐Type Reductive Coupling

Abstract

The current approaches capable of affording conjugated porous networks (CPNs) still rely on solution‐based coupling reactions promoted by noble metal complexes or Lewis acids, on‐surface polymerization conducted in ultrahigh‐vacuum environment at very high temperatures (>200 °C), or mechanochemical Scholl‐type reactions limited to electron‐rich substrates. To develop simple and scalable approaches capable of making CPNs under neat and ambient conditions, herein, a novel and complementary method to the current oxidative Scholl coupling processes is demonstrated to afford CPNs via direct aromatic ring knitting promoted by mechanochemical Ullmann‐type reactions. The key to this strategy lies in the dehalogenation of aromatic halides in the presence of Mg involving the formation of Grignard reagent intermediates. Products (Ph‐CPN‐1) obtained via direct CC bond formation between 1,2,4,5‐tetrabromobenzene (TBB) monomer feature high surface areas together with mesoporous architecture. The versatility of this approach is confirmed by the successful construction of various CPNs via knitting of the corresponding aromatic rings (e.g., pyrene and triphenylene), and even highly crystalline graphite product was obtained. The CPNs exhibit good electrochemical performance as the anode material in lithium‐ion batteries (LIBs). This approach expands the frontiers of CPN synthesis and provides new opportunities to their scalable applications.

The mechanochemical synthesis of polymers

“…As a result, the aromatic ring-knitting reaction enables the solvent-free and straightforward synthesis of prospective electrode materials and illustrates the possibility of using various reaction types for the mechanochemical synthesis of porous polymers. 298 …”

The Mechanochemical Synthesis and Activation of Carbon‐Richπ‐Conjugated Materials

“…Nonetheless, due to their unique features, the as-prepared CPNs have been evaluated as electrode materials in Li-ion batteries and showed long-term cycling stability and a rate performance superior to natural graphite making them promising candidates as electrode materials. [90] Another class of porous materials that has been used for electrochemical energy storage, is (doped) nanoporous carbon. [91] In this context, Zhang, Wang, and coworkers described a ball Scheme 10.…”

“…They reasoned that the provided mechanical energy would be sufficient to start the insertion of Mg species into the CX bond, resulting in a rapid and efficient solid‐state formation of the final CPN by a reductive Ullmann‐type coupling. However, being a mild and straightforward synthesis compared to other methods described, [ 90 ] the influence of mechanochemistry on the material properties was only discussed briefly. For instance, a small particle size, conjugated architecture, permanent porosity, and a robust network were mentioned, but only the degree of polymerization as well the porosity were correlated directly with the milling time.…”

“…[ 83 , 87 ] Recently, Dai and coworkers reported a mechanochemical protocol that does not rely on the use of noble metal complexes, Lewis acids, electron‐rich substrates, or ultrahigh‐vacuum environment at high temperatures for the synthesis of CPNs. [ 90 ] Instead, halogenated arenes and Mg are used to perform reductive dehalogenation by an Ullmann‐type coupling. After the arenes are knitted together and depending on the used monomer, porous materials consisting of meso‐ and macropores or highly crystalline graphite structures were obtained.…”

“…Nonetheless, due to their unique features, the as‐prepared CPNs have been evaluated as electrode materials in Li‐ion batteries and showed long‐term cycling stability and a rate performance superior to natural graphite making them promising candidates as electrode materials. [ 90 ]…”