Noncovalent dimerization after enediyne cyclization on Au(111)

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 (Bergman) 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 noncovalently bound dimers on the surface. The reaction mechanism and driving forces behind noncovalent association are discussed in light of density functional theory calculations.Research was supported by the U.S. Department of Energy Office of Basic Energy Sciences Nanomachine Program under Contract No. DE-AC02-05CH11231 (STM imaging), by the Office of Naval Research BRC Program (molecular synthesis), by the European Research Council Grants ERC-2010-AdG267374-DYNamo and ERC-2014-STG-635919-SURFINK (computational resources and surface analysis, respectively), by Spanish Grant No. FIS2013-46159-C3-1-P (simulated reaction landscape), and by Grupos Consolidados UPV/EHU del Gobierno Vasco No. IT-578-13 (simulated dimer binding energy). A.P.P. acknowledges postdoctoral fellowship support rom “Ayuda para la Especializacion de Personal Investigador ́ del Vicerrectorado de Investigacion de la UPV/EHU-2013 ́ ” and from the Spanish “Juan de la Cierva-incorporacioń ” program (IJCI-2014-20147).Peer reviewe