Using Achiral Monomers to Synthesize Organometallic Chiral Copolymers on an Achiral Surface

Preparing chiral polymers by using achiral building blocks in an achiral reaction environment is very demanding because this strategy avoids the use of expensive chiral reagents. Here, a surface-confined and sequence-controlled chiral copolymer is synthesized by the organometallic reactions between the achiral precursors 4,4″-dibromo-1,1':3',1''-terphenyl and 1-ethynyl-4-[2-(4-ethynylphenyl)ethynyl]benzene on an achiral Ag(111) surface. Combined scanning tunneling microscopy and density functional theory explorations show that the terminal alkyne and aromatic bromide precursors undergo dehydrogenated and debrominated metalations with surface Ag adatoms to yield the organometallic polymeric products. Despite the achiral precursors and substrate surface employed, the [phenyl-Ag-alkynyl-Ag-phenyl-Ag]<i>_n</i> copolymer with a chiral adsorption configuration stands out from various achiral competitors to become the dominant copolymeric product. Mechanistic analysis reveals that such a selectivity originates from the precise control of both sequence and adsorption configuration of the polymeric product during its growth, where the interpolymer interactions play a pivotal role. These interpolymer interactions also drive the enantioselective assembly of the copolymers to form the chiral domains, which achieves chirality transfer from the single-molecular to supramolecular level. These findings demonstrate the power of surface chemistry in creating chiral nanostructures from achiral precursors, which may help achieve chiral surface functionalization.