Apparent Copper(II)-Accelerated Azide−Alkyne Cycloaddition

Abstract

Cu(II) salts accelerate azide-alkyne cycloaddition reactions in alcoholic solvents without reductants such as sodium ascorbate. Spectroscopic observations suggest that Cu(II) undergoes reduction to catalytic Cu(I) species via either alcohol oxidation or alkyne homocoupling, or both, during an induction period. The reactions involving 2-picolylazide are likely facilitated by its chelation to Cu(II). The highly exothermic reaction between 2-picolylazide and propargyl alcohol completes within 1-2 min in the presence of as low as 1 mol % Cu(OAc)(2).

Ligand‐Assisted, Copper(II) Acetate‐Accelerated Azide–Alkyne Cycloaddition

“…[5] Our group reported the use of copper(II) acetate (Cu-A C H T U N G T R E N N U N G (OAc) 2 ) to promote CuAAC reactions in the absence of an added reducing agent, for example, sodium ascorbate. [6] We hypothesized that the catalytic copper(I) species is generated upon reduction of copper(II) by either an oxidizable solvent such as methanol [7] or the terminal alkyne substrate by means of the oxidative homocoupling reaction. [8] A subset of the azide substrates rapidly convert to triazole products under the CuA C H T U N G T R E N N U N G (OAc) 2 -mediated conditions.…”

Computational investigations of click-derived 1,2,3-triazoles as keystone ligands for complexation with transition metals: a review

“…This displacement of two axial N2 atoms from the basal plane formed by two pyridine N4 atoms and two chloride ions leads to a pyramidal distortion of the octahedral geometry. In another reported ionic complex of [Cu(L1) 2 (CH 3 CN)-(ClO 4 )](ClO 4 ), 176 the copper cation displays the square-planar geometry of four nitrogen atoms with CH 3 CN and ClO 4 À ligands at the axial positions.…”

Physical and structural properties of [Cu(BOT1)Cl]Cl, a fluorescent imaging probe for HNO

“…The shorter Cu-Cl interaction is trans to the longer copper-N(triazole) distance mentioned above. The crystal structure of a copper(II) complex of an analogous ligand in which the BODIPY chromophore of BOT1 is replaced by a benzyl group has previously been reported [34]. This complex exhibits structural features similar to those of [Cu(BOT1)Cl] + .…”