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J Am Chem Soc. 2016 May 11;138(18):5837-47. doi: 10.1021/jacs.5b11594. Epub 2016 May 2.

Driving Forces for Covalent Assembly of Porphyrins by Selective C-H Bond Activation and Intermolecular Coupling on a Copper Surface.

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Department of Physics, King's College London , London, Strand WC2R 2LS, United Kingdom.
School of Mathematics and Physics, University of Lincoln , Brayford Pool, Lincoln LN6 7TS, United Kingdom.
Surface Science Research Center and Department of Chemistry, University of Liverpool , Liverpool L69 3BX, United Kingdom.
School of Chemistry, The University of Nottingham , University Park, Nottingham NG7 2RD, United Kingdom.


Recent synthesis of covalent organic assemblies at surfaces has opened the promise of producing robust nanostructures for functional interfaces. To uncover how this new chemistry works at surfaces and understand the underlying mechanisms that control bond-breaking and bond-making processes at specific positions of the participating molecules, we study here the coupling reaction of tetra(mesityl)porphyrin molecules, which creates covalently connected networks on the Cu(110) surface by utilizing the 4-methyl groups as unique connection points. Using scanning tunneling microscopy (STM), state-of-the-art density functional theory (DFT), and Nudged Elastic Band (NEB) calculations, we show that the unique directionality of the covalent bonding is found to stem from a chain of highly selective C-H activation and dehydrogenation processes, followed by specific intermolecular C-C coupling reactions that are facilitated by the surface, by steric constraints, and by anisotropic molecular diffusion. These insights provide the first steps toward developing synthetic rules for complex two-dimensional covalent organic chemistry that can be enacted directly at a surface to deliver specific macromolecular structures designed for specific functions.


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