Transferring axial molecular chirality through a sequence of on-surface reactions
April 29, 2020
Néstor Merino-Díez, Mohammed S. G. Mohammed, Jesús Castro-Esteban, Luciano Colazzo, Alejandro Berdonces-Layunta, James Lawrence, J. Ignacio Pascual, Dimas G. de Oteyza and Diego Peña
Chemical Science 11, 5441-5446 (2020)
In this work we demonstrated that the on-surface polycondensation of 2,20-dibromo-9,90-bianthracene (DBBA) led to bianthryl polymers that could subsequently be transformed into prochiral (3,1)-graphene nanoribbons (GNRs) by cyclodehydrogenation, directly on a metallic surface. We were able to isolate enantiomerically enriched samples of (+) and (−)-DBBA by HPLC (98:2 enantiomeric ratio). DBBA enantiomers were independently deposited on Au(111) surface. Analysis by STM allowed us to establish the absolute configuration of the enantiomers (S for (+)-DBBA; R for (−)-DBBA) and to study how the inherent handedness of the precursors evolves through the different reactions performed on the substrate. The chirality transfer process is demonstrated through a multistep on-surface synthesis process that also involves chiral polymers as intermediates.
Fine management of chiral processes on solid surfaces has progressed over the years, yet still faces the need for the controlled and selective production of advanced chiral materials. Here, we report on the use of enantiomerically enriched molecular building blocks to demonstrate the transmission of their intrinsic chirality along a sequence of on-surface reactions. Triggered by thermal annealing, the on-surface reactions induced in this experiment involve firstly the coupling of the chiral reactants into chiral polymers and subsequently their transformation into planar prochiral graphene nanoribbons. Our study reveals that the axial chirality of the reactant is not only transferred to the polymers, but also to the planar chirality of the graphene nanoribbon end products. Such chirality transfer consequently allows, starting from adequate enantioenriched reactants, for the controlled production of chiral and prochiral organic nanoarchitectures with pre-defined handedness.