Synthesis of Mono- and Bis-N-Heterocyclic Carbene Copper(I) Complexes via Decarboxylative Generation of Carbenes

Abstract

Zwitterionic carboxylates can be thermally decarboxylated in the presence of copper salts to form NHC-copper com­plexes. The selective formation of either mono- or bis-NHC complexes is possible through simple control of the molar equivalents of the copper salt. A variety of different NHC ligands with either saturated or unsaturated backbones or bearing N-aryl or N-alkyl substituents can be complexed to copper.

Key words

oxidative coupling - N-heterocyclic carbenes - copper - catalysis - decarboxylation

References

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15

One advantage of the decarboxylation method is the absence of strong bases such as potassium tert-butoxide, which has been shown to react with Cu(NHC)₂X complexes to form an unwanted byproduct Cu(NHC)(Ot-Bu). See ref. 7.

16

Although complexes 6a-c are depicted as ionic, at this time there is yet no proof as to whether the halide counterions are ligated to the copper atom or not.

17

The ^¹H and ^¹³C NMR spectra for Cu(NHC)X and Cu(NHC)₂X complexes are very similar. The complexes can be easily distinguished by TLC [the Cu(NHC)₂X complexes are much more polar than the analogous Cu(NHC)X complexes] and by MS.

20

Pevere V.; FR 2,921,924, 2009