Theoretical Studies of the Mechanism of Ullmann Coupling of Naphthyl Halogen Derivatives to Binaphtyl on Coinage Metals

Abstract

In the field of on-surface synthesis, 2D molecular networks are formed by C-C coupling reactions. The on-surface Ullmann coupling reaction results in the formation of a new C-C bond by dehalogenation of aryl halide precursor molecules and stabilization of the resulting radicals by a catalytic metal surface, most commonly a copper surface. However, the reaction is also performed on silver and gold surfaces, on which different influences on the reaction behavior are observed. Knowledge of the thermodynamics and kinetics of these reactions to elucidate the full reaction mechanism and the effects of various surfaces and molecules is sparse and can be investigated by using quantum chemical calculations. Here, we present the elucidation of the reaction mechanisms of several naphthalene halide derivatives on (111) coin metal surfaces to binaphthalene molecules using density functional theory with a dispersion correction. We compare the different reaction steps and the whole reaction mechanism of single halogenated naphthalene with two halogens (Br, I) and changed position on the naphthalene on the three different coinage metal surfaces, copper, silver, and gold. As a result, we show that the qualitative order of the reaction barriers on the different catalytic surface metals is not the same for all of the reaction steps. Even the highly reactive copper surface inhibits certain reaction steps, such as the C-C coupling reaction, due to steric hindrances and the stability of the organometallic bond. Overall, we present detailed insights into the mechanism of Ullmann coupling reactions on coin metal surfaces, which will help in the design of novel precursors and the selection of favorable surface metals.