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Free keywords:
on-surface chemistry; enediyne cyclization; C1–C6 (Bergman) cyclization; C1–C5 (Schreiner-Pascal) cyclization; dipole-dipole interactions; non-covalent aggregates; scanning tunneling microscope (STM); density functional theory (DFT); Au(111); phenyl shift
Abstract:
We investigate the thermally-induced cyclization of 1,2-bis(2-phenylethynyl)benzene on Au(111) using scanning tunneling microscopy and computer simulations. Cyclization of sterically hindered enediynes is known to proceed via two competing mechanisms in solution: a classic C1–C6 or a C1–C5 cyclization pathway. On Au(111) we find that the C1–C5 cyclization is suppressed and that the C1–C6 cyclization yields a highly strained bicyclic olefin whose surface chemistry was hitherto unknown. The C1–C6 product self-assembles into discrete non-covalently bound dimers on the surface. The reaction mechanism and driving forces behind non-covalent association are discussed in light of density functional theory calculations.
