On-Surface Azide–Alkyne Cycloaddition Reaction: Does It Click with Ruthenium Catalysts?

Abstract

Owing to its simplicity, selectivity, high yield, and the absence of byproducts, the “click” azide–alkyne reaction is widely used in many areas. The reaction is usually catalyzed by copper(I), which selectively produces the 1,4-disubstituted 1,2,3-triazole regioisomer. Ruthenium-based catalysts were later developed to selectively produce the opposite regioselectivity—the 1,5-disubstituted 1,2,3-triazole isomer. Ruthenium-based catalysis, however, remains only tested for click reactions in solution, and the suitability of ruthenium catalysts for surface-based click reactions remains unknown. Also unknown are the electrical properties of the 1,4- and 1,5-regioisomers, and to measure them, both isomers need to be assembled on the electrode surface. Here, we test whether ruthenium catalysts can be used to catalyze surface azide–alkyne reactions to produce 1,5-disubstituted 1,2,3-triazole, and compare their electrochemical properties, in terms of surface coverages and electron transfer kinetics, to those of the compound formed by copper catalysis, 1,4-disubstituted 1,2,3-triazole isomer. Results show that ruthenium(II) complexes catalyze the click reaction on surfaces yielding the 1,5-disubstituted isomer, but the rate of the reaction is remarkably slower than that of the copper-catalyzed reaction, and this is related to the size of the catalyst involved as an intermediate in the reaction. The electron transfer rate constant ( k et ) for the ruthenium-catalyzed reaction is 30% of that measured for the copper-catalyzed 1,4-isomer. The lower conductivity of the 1,5-isomer is confirmed by performing nonequilibrium Green’s function computations on relevant model systems. These findings demonstrate the feasibility of ruthenium-based catalysis of surface click reactions and point toward an electrical method for detecting the isomers of click reactions.

Electrochemically functionalized graphene for highly sensitive detection of nitrofurazone

“…In the Nyquist plot, the semicircle diameter represents the charge transfer resistance ( R ct ), which is commonly used as an indicator for the electron transfer ability. 34 By fitting the Randles equivalent circuit (inset), 35,36 the R ct values of NFZ were measured and found to be 70.26, 60.26, 26.66 and 9.03 kΩ on the GCE (curve a), GCE-1.4 (curve b), GS/GCE (curve c) and EGS-1.4/GCE (curve d). As shown in Table S2,† smaller R ct indicates that EGS-1.4/GCE is much more active for the oxidation of NFZ, and consequently greatly improves the NFZ response signals.…”

An Overview of Synthetic Approaches towards 1,2,3-Triazoles

“…(K) In a recent study, Li et al 27 illustrated the viability of the RuAAC reaction as a surface chemical process and provided evidence that the catalyst’s size influences the reaction kinetics. The researchers conducted a hydrosilylation reaction between oxide-free silicon (Si–H) electrodes and 1,8-nonadiyne, followed by treatment with ruthenium as a catalyst to yield the 1,5-isomer of 1,2,3-triazoles.…”

Terminal Deuterium Atoms Protect Silicon from Oxidation

“…Silicon electrodes were cleaned and etched by the following literature procedures. 15,39,54,55 In brief, for Si−D surfaces, silicon wafers were cut into pieces (approximately 1 × 1 cm), cleaned in hot Piranha solution (130 °C, 3:1(v/v) mixture of concentrated sulfuric acid to 30% hydrogen peroxide) for 20 min (S-2, Figure 1), then rinsed with water and etched in a solution of anhydrous potassium fluoride (KF)…”

“…Silicon electrodes were cleaned and etched by the following literature procedures. ,,, In brief, for Si–D surfaces, silicon wafers were cut into pieces (approximately 1 × 1 cm), cleaned in hot Piranha solution (130 °C, 3:1­(v/v) mixture of concentrated sulfuric acid to 30% hydrogen peroxide) for 20 min ( S-2 , Figure ), then rinsed with water and etched in a solution of anhydrous potassium fluoride (KF) (40 wt % in D 2 O) to which were added a few drops of 37% deuterated hydrochloric acid (DCl) and a small quantity of anhydrous sodium sulfite under a stream of argon for 13 min. The etched surfaces were rinsed with D 2 O water and CD 2 Cl 2 before being placed in a deoxygenated sample of 1,8-nonadiyne.…”

“…In recent years, there has been increasing interest in modifying Si with organic monolayers to form a hybrid technology that combines the semiconducting properties of silicon with the properties of organic molecules. – The applications of this technology include sensors, – photovoltaics, – and molecular electronics devices. – In most of these applications, the typical procedure is first to remove the natural oxide layer that forms on the Si surface to expose the reactive Si–H surface. The Si–H surface is then reacted via a hydrosilylation reaction mainly with alkenes or alkynes. ,– The reaction yields an organic monolayer of density ∼50%, and the remaining unreacted sites stay as Si–H.…”