Covalent‐Bond Formation via On‐Surface Chemistry

Abstract

In this Review article pioneering work and recent achievements in the emerging research area of on-surface chemistry is discussed. On-surface chemistry, sometimes also called two-dimensional chemistry, shows great potential for bottom-up preparation of defined nanostructures. In contrast to traditional organic synthesis, where reactions are generally conducted in well-defined reaction flasks in solution, on-surface chemistry is performed in the cavity of a scanning probe microscope on a metal crystal under ultrahigh vacuum conditions. The metal first acts as a platform for self-assembly of the organic building blocks and in many cases it also acts as a catalyst for the given chemical transformation. Products and hence success of the reaction are directly analyzed by scanning probe microscopy. This Review provides a general overview of this chemistry highlighting advantages and disadvantages as compared to traditional reaction setups. The second part of the Review then focuses on reactions that have been successfully conducted as on-surface processes. On-surface Ullmann and Glaser couplings are addressed. In addition, cyclodehydrogenation reactions and cycloadditions are discussed and reactions involving the carbonyl functionality are highlighted. Finally, the first examples of sequential on-surface chemistry are considered in which two different functionalities are chemoselectively addressed. The Review gives an overview for experts working in the area but also offers a starting point to non-experts to enter into this exciting new interdisciplinary research field.

Reaction Selectivity in On‐Surface Chemistry by Surface Coverage Control—Alkyne Dimerization versus Alkyne Trimerization

“…On-surface synthesis, by which well-defined covalent nanostructuresc an be constructed at noble metal surfaces, is an important and steadily growing research area in molecular nanotechnology. [1][2][3][4][5][6][7] Recently,v arioust wo-dimensional reactions, such as the Ullman coupling, [8][9][10][11][12] iminec oupling, [13][14][15] dehydration of boronica cids, [16] carbene dimerization, [17,18] acylation, [19,20] cycloaddition, [21][22][23][24] decarboxylation, [25] and dehydrogenation, [10,[26][27][28][29] have been disclosed.W hereasl igands can steer reactiono utcome( selectivity) in solution phase transition-metal-based catalysis, ligandsa re missing in on-surface chemistry and hence such at ool is not available in this field. Therefore, the general question of how to steer/controlreactivity in on-surface chemistry arises.…”

Direct Formation of C−C Triple‐Bonded Structural Motifs by On‐Surface Dehalogenative Homocouplings of Tribromomethyl‐Substituted Arenes

“…[1][2][3][4] As ar esult, many unexpected reactions have been achieved on different surfaces. [1][2][3][4] As ar esult, many unexpected reactions have been achieved on different surfaces.…”

On‐Surface Synthesis of Adenine Oligomers via Ullmann Reaction

“…Considering the rapidly developing field of on‐surface synthesis, it would be highly intriguing to combine DNA bases and on‐surface synthesis strategy with the aim of synthesis of man‐made quasi DNA oligomers on the surface. Ullmann reaction has been extensively studied on surfaces and considered as one of the most versatile approaches to building up covalently linked nanostructures by well‐designed halogenated precursors . In this work, we have designed and synthesized a halogenated derivative of adenine molecule, i.e., 9‐[3,5‐dibromophenyl]‐9 H ‐purin‐6‐amine (shortened as DBPA, as shown in Scheme ), in which the dibromophenyl group is modified on the N9 site (normally connected with the sugar moiety in DNA) to simply mimic the naturally occurring nucleotides and also give access to the formation of backbones via Ullmann reaction.…”

“…[4, 8-10, 28, 29] Althougha dvanced deposition strategies have been successfully employed, it is nevertheless of general interest to explore comparatively simple routes toward in situ synthesis of DNA macromolecules on surfaces. Considering the rapidly developing field of on-surface synthesis, [30][31][32][33][34] it would be highly intriguing to combine DNA bases and on-surface synthesis strategy with the aim of synthesis of man-made quasi DNA oligomers on the surface. Ullmann reactionh as been extensively studied on surfaces and considered as one of the most versatile approaches to building up covalently linked nanostructures by well-designed halogenated precursors.…”

“…Ullmann reactionh as been extensively studied on surfaces and considered as one of the most versatile approaches to building up covalently linked nanostructures by well-designed halogenated precursors. [30,31,34] In this work, we have designed and synthesized ah alogenated derivative of adenine molecule, i.e.,9 -[3,5-dibromophenyl]-9H-purin-6-amine (shortened as DBPA, as shown in Scheme1), in which the dibromophenylg roup is modified on the N9 site (normally connected with the sugar moiety in DNA) to simply mimic the naturally occurring nucleotides and also give access to the formation of backbones via Ullmannr eaction. We choose the Au(111)s urface as the template because the interactions between DNA bases andA u(111)s ubstrate are relatively weak and the intermolecular interactions are thus dominant.…”