Identification of Topotactic Surface‐Confined Ullmann‐Polymerization

Abstract

On‐surface Ullmann coupling is an established method for the synthesis of 1D and 2D organic structures. A key limitation to obtaining ordered polymers is the uncertainty in the final structure for coupling via random diffusion of reactants over the substrate, which leads to polymorphism and defects. Here, a topotactic polymerization on Cu(110) in a series of differently‐halogenated para‐phenylenes is identified, where the self‐assembled organometallic (OM) reactants of diiodobenzene couple directly into a single, deterministic product, whereas the other precursors follow a diffusion driven reaction. The topotactic mechanism is the result of the structure of the iodine on Cu(110), which controls the orientation of the OM reactants and intermediates to be the same as the final polymer chains. Temperature‐programmed X‐ray photoelectron spectroscopy and kinetic modeling reflect the differences in the polymerization regimes, and the effects of the OM chain alignments and halogens are disentangled by Nudged Elastic Band calculations. It is found that the repulsion or attraction between chains and halogens drive the polymerization to be either diffusive or topotactic. These results provide detailed insights into on‐surface reaction mechanisms and prove the possibility of harnessing topotactic reactions in surface‐confined Ullmann polymerization.

On‐Surface Synthesis of Porphyrin‐Complex Multi‐Block Co‐Oligomers by Defluorinative Coupling

“…[11] Taking advantage of different reaction temperatures required for each CÀ X bond cleavage, a stepwise synthesis could be performed if more than two kinds of halogen atoms were substituted to precursor molecules. [12] Nevertheless, it is still challenging to construct highly-ordered sequence structures based on this strategy because of the fact that i) most of the reactants are activated at given substrate temperatures, ii) the activation temperatures at the different CÀ X bonds are not well-separated, [13] and iii) the activated reactants can also be terminated by residual hydrogen atoms (short-lived). [14] Therefore, it is quite beneficial to develop an alternative on-surface sequential reaction to circumvent this issue.…”

Molecular insight into on-surface chemistry of an organometallic polymer

“…In contrast, the reactivity of extended molecular systems formed by chemically bonded monomeric building blocks on surfaces has been scarcely explored. 29 The reactive extended molecular systems can be envisioned as the polymeric organometallic (OM) intermediates of the most frequently employed surface reactions, i.e., Ullmann [30][31][32] and Glaser 33 couplings, and are believed to play a role in producing highquality products. 34 Therefore, understanding the on-surface chemistry of extended molecular systems becomes highly desirable.…”

Toward Molecular Fractals on Surfaces: Designing Covalent Structures with the Monte Carlo Simulation Method

“…Moreover, to create persistent fractal molecular structures, the covalent linkage of specially designed tectons has also been used, including dehydration reactions, polycondensation of boronic compounds, , Schiff-base reactions, thioether linkage, and multifold Suzuki coupling . Another useful approach to fabricate covalent polymeric structures on surfaces has been the Ullmann coupling, which involves halogenated aromatics and catalytically active metal substrates and enables the synthesis of molecular constructs such as wires, − nanoribbons, − chiral dimers, cyclic oligomers, , networks, − and others . In this heterogeneous catalytic reaction, aryl halides split off halogen atoms upon adsorption on coinage metals such as copper, silver, and gold and further recombine to form covalent polymeric structures cemented by carbon–carbon bonds.…”