Isomerization of Organometallic Polymers on Ag(111): Revealing the Intermolecular Hydrogen Transfer Mechanism.

Dehalogenation plays a crucial role in on-surface synthesis, but the bond-forming sites in dehalogenation occasionally differ from the original halogen-substituted sites, leading to unexpected products. Revealing its mechanism is essential for the atomically precise fabrication of low-dimensional nanomaterials, although it remains elusive. Herein, we report an isomerization of organometallic polymers derived from debromination on Ag(111) and elucidate the mechanism involving intermolecular hydrogen transfer via combining scanning tunneling microscopy, noncontact atomic force microscopy, and density functional theory calculations. At room temperature, the precursor 1,4-bis(3-bromothiophen-2-yl)benzene undergoes surface-assisted debromination on Ag(111), forming two organometallic polymers where the bond-forming sites correspond to the original debromination sites. Upon annealing to 393 K, the isomerization of organometallic polymers generates a linear organometallic polymer, where the bond-forming sites mismatched with the original debromination sites. Control experiments combined with theoretical calculations demonstrate that the unexpected isomerization proceeds through the dissociation of polymer chains into surface-stabilized diradical monomers or oligomers, intermolecular hydrogen transfer, and the final recombination of surface-stabilized radicals with Ag adatoms.