Abstract
A series of copper complexes (3–6) stabilized by 1,2,3-triazole-tethered N-heterocyclic carbene ligands have been prepared via simple reaction of imidazolium salts with copper powder in good yields. The structures of bi- and trinuclear copper complexes were fully characterized by NMR, elemental analysis (EA), and X-ray crystallography. In particular, [Cu2(L2)2](PF6)2 (3) and [Cu2(L3)2](PF6)2 (4) were dinuclear copper complexes. Complexes [Cu3(L4)2](PF6)3 (5) and [Cu3(L5)2](PF6)3 (6) consist of a triangular Cu3 core. These structures vary depending on the imidazolium backbone and N substituents. The copper–NHC complexes tested are highly active for the Cu-catalyzed azide–alkyne cycloaddition (CuAAC) reaction in an air atmosphere at room temperature in a CH3CN solution. Complex 4 is the most efficient catalyst among these polynuclear complexes in an air atmosphere at room temperature.
Highlights
N-Heterocyclic carbene (NHC) have interesting electronic and structural properties
As seen in Scheme 1, copper–NHC complexes 3–6 can be obtained in 52–90% yields via directly reacting the corresponding imidazolium salts with an excess of copper powder in CH3CN at 50 °C for 5 h
A red binuclear Cu(I) complex 3 was obtained in 57% yield when we reacted pyrimidyl benzimidazolium salt 1b with copper powder
Summary
N-Heterocyclic carbene (NHC) have interesting electronic and structural properties. This resulted in their use as versatile ligands in organometallic chemistry and homogeneous catalysis [1,2,3,4,5,6,7,8,9,10,11,12]. The synthesis, structural characterization, and catalytic properties of a few copper-1,2,3-triazole-tethered NHC complexes is reported.
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