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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.


Ball-and-stick model [42–43] of a single crystal X-ray structure of hexafluorophosphate salt 1b (CCDC 1472789). Color code: black carbon, grey hydrogen, yellow sulfur, blue nitrogen, magenta phosphorus, green fluorine.
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Figure 1: Ball-and-stick model [42–43] of a single crystal X-ray structure of hexafluorophosphate salt 1b (CCDC 1472789). Color code: black carbon, grey hydrogen, yellow sulfur, blue nitrogen, magenta phosphorus, green fluorine.

Mentions: We herein report the synthesis of an ethylene-linked bisthiazol-2-ylidene dicopper(I) complex 2 that features high catalytic activity in CuAAC reactions. The advantage of this new complex 2 in comparison to dicopper complexes previously described by our research group [40] is its less time-consuming and more cost-efficient synthesis. Commercially available, inexpensive 4,5-dimethylthiazole is used as azole starting material instead of 4-aryl-1,2,4-triazoles. The precursor 1a for the NHC ancillary ligand is synthesized via a double SN2-reaction of two equivalents of thiazole derivative with 1,2-dibromoethane. In order to avoid the presence of halide ions as inhibitory ligands for copper(I) [2,41], bisthiazolium hexafluorophosphate 1b was obtained by a salt metathesis from bromide salt 1a with aqueous hexafluorophosphoric acid (Fig. 1).


Dinuclear thiazolylidene copper complex as highly active catalyst for azid – alkyne cycloadditions
Ball-and-stick model [42–43] of a single crystal X-ray structure of hexafluorophosphate salt 1b (CCDC 1472789). Color code: black carbon, grey hydrogen, yellow sulfur, blue nitrogen, magenta phosphorus, green fluorine.
© Copyright Policy - Beilstein
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4979731&req=5

Figure 1: Ball-and-stick model [42–43] of a single crystal X-ray structure of hexafluorophosphate salt 1b (CCDC 1472789). Color code: black carbon, grey hydrogen, yellow sulfur, blue nitrogen, magenta phosphorus, green fluorine.
Mentions: We herein report the synthesis of an ethylene-linked bisthiazol-2-ylidene dicopper(I) complex 2 that features high catalytic activity in CuAAC reactions. The advantage of this new complex 2 in comparison to dicopper complexes previously described by our research group [40] is its less time-consuming and more cost-efficient synthesis. Commercially available, inexpensive 4,5-dimethylthiazole is used as azole starting material instead of 4-aryl-1,2,4-triazoles. The precursor 1a for the NHC ancillary ligand is synthesized via a double SN2-reaction of two equivalents of thiazole derivative with 1,2-dibromoethane. In order to avoid the presence of halide ions as inhibitory ligands for copper(I) [2,41], bisthiazolium hexafluorophosphate 1b was obtained by a salt metathesis from bromide salt 1a with aqueous hexafluorophosphoric acid (Fig. 1).

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.