Surface‐Dependent Chemoselectivity in C−C Coupling Reactions. Issue 25 (14th May 2019)

• Record Type: Journal Article
• Authors: Chen, Zhi; Lin, Tao; Zhang, Liding; Zhang, Lei; Xiang, Bingxi; Xu, Hu; Klappenberger, Florian; Barth, Johannes V.; Klyatskaya, Svetlana; Ruben, Mario
• Is Part Of: Angewandte Chemie international edition. Volume 58:Issue 25(2019)
• Page Start: 8356
• Page End: 8361
• Publication Date: 2019-05-14
• Subjects: alkenes -- alkynes -- chemoselectivity -- cross-coupling -- scanning tunneling microscopy; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201900636
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Surface‐confined covalent coupling reactions of the linear compound 4‐(but‐3‐en‐1‐ynyl)‐4′‐ethynyl‐1, 1′‐biphenyl (1 ), which contains one alkyne and one enyne group on opposing ends, have been investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The reactions show a surface‐dependent chemoselectivity: on Au(111), compound 1 preferentially yields cyclotrimerization products, while on Cu(111), a selective coupling between the enyne and alkyne groups is observed. Linear, V‐shaped string formations combined with Y‐shaped bifurcation motifs result in a random reticulation on the entire surface. DFT calculations show that the C−H⋅⋅⋅π δ− transition state of the reaction between the deprotonated alkyne group and a nearby H‐donor of the alkene group plays a key role in the mechanism and high chemoselectivity. This study highlights a concept that opens new avenues to the surface‐confined synthesis of covalent carbon‐based sp–sp 2 polymers. Abstract : Knitting the nanonet : A molecule with one alkyne and one enyne group shows chemoselectivity in on‐surface C−C coupling reactions depending on the metal substrate. Cyclotrimerization of the alkynes on Au(111) and cross‐coupling between the enyne group and the alkyne group on Cu(111) give access to 2D covalent networks, which are observed experimentally and confirmed by DFT calculations.