tel Copper(I) complexes comprising different N-heterocyclic carbene ligands were prepared via in situ deprotonation and metallation. Depending on the wingtip groups on the carbene ligand (alkyl vs. aryl, chelating or monodentate), a variety of different structural motifs were identified, such as a trigonal planar geometry (alkyl wingtips) and an unprecedented see-saw-type structure (pyridinyl wingtip groups). While aryl wingtip groups increase the stability of the complexes, alkyl substituents induce rapid demetallation in the presence of moisture. The reactivity of these complexes was used to establish a carbene-transfer protocol, which is illustrated by the formation of new cyclic thiourea compounds (transfer to sulfur) and new (carbene)ruthenium(II) complexes (transfer to ruthenium). This suggests that (carbene)copper(I) complexes could become valuable alternatives to (carbene)silver(I) complexes for synthesizing (carbene)metal systems via transmetallation.

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