The synthesis of polycyclic aromatic hydrocarbons containing various non-benzenoid rings remains a big challenge facing contemporary organic chemistry despite a considerable effort made over the last decades. Herein, we present a novel route, employing on-surface chemistry, to synthesize nonalternant polycyclic aromatic hydrocarbons containing up to four distinct kinds of non-benzenoid rings. We show that the surface-induced mechanical constraints imposed on strained helical reactants play a decisive role leading to the formation of products, energetically unfavorable in solution, with a peculiar ring current stabilizing the aromatic character of the π-conjugated system. Determination of the chemical and electronic structures of the most frequent product reveals its closed-shell character and low band gap. The present study renders a new route for the synthesis of novel nonalternant polycyclic aromatic hydrocarbons or other hydrocarbons driven by internal stress imposed by the surface not available by traditional approaches of organic chemistry in solution.
Catalysis, considered as the heart of modern science, has changed the paradigm of constructing molecular complexity with great selectivity and efficiency. Over the years, the field of catalysis has made a paramount impact on science and technology because of its rapid emergence in the development of new synthetic methodologies that are not only greener but also cost, time, yield, and labor-effective. The legacy of catalysis in synthetic organic chemistry has mainly been promoted by two key players: transition-metal catalysis and organocatalysis. The scientific contribution and societal impact of these two types of catalysis has been acknowledged with the Nobel Prizes in the year 2001 (Knowles, Noyori, and Sharpless for stereoselective catalysis), 2005 (Chauvin, Grubbs, and Schrock for olefin metathesis), 2010 (Heck, Negishi, and Suzuki for palladium-catalyzed cross-coupling reactions) and recently in 2021 (List and MacMillan for asymmetric organocatalysis).Although it is almost impossible to compare which type of catalysis (metal-or organo-catalysis) is superior because of their unique characteristic reactivity profiles, transition-metal catalysis has traditionally been considered as a strong pillar of catalysis and has mostly dominated the field of organic synthesis. The ability of transition metals to shuttle between different oxidation states while forming complexes with the reagents in a catalytic cycle allows them to achieve unprecedented and non-conventional transformations. Moreover, the reactivity and selectivity of these metal complexes can be finetuned according to the requirement of the catalytic process with the assistance of different factors, such as steric and electronic nature of metal-coordinated ligands and counterions. Thereby, these processes are in general highly efficient and hold tremendous potential for the development of new
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