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Dinuclear thiazolylidene copper complex as highly active catalyst for azid – alkyne cycloadditions

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ABSTRACT

A dinuclear N-heterocyclic carbene (NHC) copper complex efficiently catalyzes azide–alkyne cycloaddition (CuAAC) “click” reactions. The ancillary ligand comprises two 4,5-dimethyl-1,3-thiazol-2-ylidene units and an ethylene linker. The three-step preparation of the complex from commercially available starting compounds is more straightforward and cost-efficient than that of the previously described 1,2,4-triazol-5-ylidene derivatives. Kinetic experiments revealed its high catalytic CuAAC activity in organic solvents at room temperature. The activity increases upon addition of acetic acid, particularly for more acidic alkyne substrates. The modular catalyst design renders possible the exchange of N-heterocyclic carbene, linker, sacrificial ligand, and counter ion.

No MeSH data available.


Time-conversion-diagram of the CuAAC reaction of benzyl azide with either phenylacetylene or ethyl propiolate in the presence of copper complex 2 (1.8 mol % for reaction with phenylacetylene, 0.9 mol % for reaction with ethyl propiolate) or in presence of CuOAc (saturated homogeneous solution) under an atmosphere of nitrogen in CD2Cl2 at rt (conversion referred to benzyl azide); reaction with phenylacetylene: green triangles (complex 2 without additional HOAc), blue dots (complex 2 in presence of 9 mol % additional HOAc) and black dots (CuOAc solution); reaction with ethyl propiolate: yellow diamonds (complex 2 without additional HOAc), red squares (complex 2 in presence of 9 mol % additional HOAc) and grey triangles (CuOAc solution).
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Figure 2: Time-conversion-diagram of the CuAAC reaction of benzyl azide with either phenylacetylene or ethyl propiolate in the presence of copper complex 2 (1.8 mol % for reaction with phenylacetylene, 0.9 mol % for reaction with ethyl propiolate) or in presence of CuOAc (saturated homogeneous solution) under an atmosphere of nitrogen in CD2Cl2 at rt (conversion referred to benzyl azide); reaction with phenylacetylene: green triangles (complex 2 without additional HOAc), blue dots (complex 2 in presence of 9 mol % additional HOAc) and black dots (CuOAc solution); reaction with ethyl propiolate: yellow diamonds (complex 2 without additional HOAc), red squares (complex 2 in presence of 9 mol % additional HOAc) and grey triangles (CuOAc solution).

Mentions: To test the catalytic performance of complex 2 with the help of continuous NMR spectroscopy, the reaction of benzyl azide with either phenylacetylene or ethyl propiolate in deuterated dichloromethane at room temperature was used (Table 1 and Fig. 2). Due to the highly exothermic nature of the triazole formation, a high dilution of the reaction mixture and low catalyst loadings are necessary to prevent a thermal runaway. In order to compare the catalytic activity of complex 2 with conventional catalysts a kinetic study with copper(I) acetate was performed. All kinetic experiments were carried out under an atmosphere of nitrogen because of the air-sensitivity of complex 2 in solution (see Supporting Information File 1 for the detailed procedure).


Dinuclear thiazolylidene copper complex as highly active catalyst for azid – alkyne cycloadditions
Time-conversion-diagram of the CuAAC reaction of benzyl azide with either phenylacetylene or ethyl propiolate in the presence of copper complex 2 (1.8 mol % for reaction with phenylacetylene, 0.9 mol % for reaction with ethyl propiolate) or in presence of CuOAc (saturated homogeneous solution) under an atmosphere of nitrogen in CD2Cl2 at rt (conversion referred to benzyl azide); reaction with phenylacetylene: green triangles (complex 2 without additional HOAc), blue dots (complex 2 in presence of 9 mol % additional HOAc) and black dots (CuOAc solution); reaction with ethyl propiolate: yellow diamonds (complex 2 without additional HOAc), red squares (complex 2 in presence of 9 mol % additional HOAc) and grey triangles (CuOAc solution).
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Related In: Results  -  Collection

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Show All Figures
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Figure 2: Time-conversion-diagram of the CuAAC reaction of benzyl azide with either phenylacetylene or ethyl propiolate in the presence of copper complex 2 (1.8 mol % for reaction with phenylacetylene, 0.9 mol % for reaction with ethyl propiolate) or in presence of CuOAc (saturated homogeneous solution) under an atmosphere of nitrogen in CD2Cl2 at rt (conversion referred to benzyl azide); reaction with phenylacetylene: green triangles (complex 2 without additional HOAc), blue dots (complex 2 in presence of 9 mol % additional HOAc) and black dots (CuOAc solution); reaction with ethyl propiolate: yellow diamonds (complex 2 without additional HOAc), red squares (complex 2 in presence of 9 mol % additional HOAc) and grey triangles (CuOAc solution).
Mentions: To test the catalytic performance of complex 2 with the help of continuous NMR spectroscopy, the reaction of benzyl azide with either phenylacetylene or ethyl propiolate in deuterated dichloromethane at room temperature was used (Table 1 and Fig. 2). Due to the highly exothermic nature of the triazole formation, a high dilution of the reaction mixture and low catalyst loadings are necessary to prevent a thermal runaway. In order to compare the catalytic activity of complex 2 with conventional catalysts a kinetic study with copper(I) acetate was performed. All kinetic experiments were carried out under an atmosphere of nitrogen because of the air-sensitivity of complex 2 in solution (see Supporting Information File 1 for the detailed procedure).

View Article: PubMed Central - HTML - PubMed

ABSTRACT

A dinuclear N-heterocyclic carbene (NHC) copper complex efficiently catalyzes azide–alkyne cycloaddition (CuAAC) “click” reactions. The ancillary ligand comprises two 4,5-dimethyl-1,3-thiazol-2-ylidene units and an ethylene linker. The three-step preparation of the complex from commercially available starting compounds is more straightforward and cost-efficient than that of the previously described 1,2,4-triazol-5-ylidene derivatives. Kinetic experiments revealed its high catalytic CuAAC activity in organic solvents at room temperature. The activity increases upon addition of acetic acid, particularly for more acidic alkyne substrates. The modular catalyst design renders possible the exchange of N-heterocyclic carbene, linker, sacrificial ligand, and counter ion.

No MeSH data available.