A series of complexes of the type (NHC)Cu-ER3] (NHC IDipp, IMes, ItBu, Me2IMe, and ER3 = SiMe2Ph, SiPh3, SnMe3) and [(NHC)Cu-R'] (NHC = IDipp; Me2IMe and. R' = Ph, C CPh) was synthesized in good yields by the reaction of the corresponding [(NHC)Cu-7 OtBu] complex with the respective silylborane pinB ER3 (pin=OCMe2CMe2O; ER3 = SiMe2Ph, SiPh3), the stannylborane ((C2H4)(iPrN)(2))B-SnMe3, or a boronic acid ester pinB R' = Ph, C=CPh). Solid structures of all complexes were systematically studied by X-ray diffraction analysis. The solid state structures of the complexes [(NHC)Cu ER3] show a dependence of the structural motif from the steric properties of the NHC ligand. The sterically demanding NHC ligands (IDipp, IMes, ItBu) lead to monomeric, linear complexes [(NHC)Cu-ER3], while, with the less demanding Me2IMe polynuclear, mu-ER3-bridged complexes with ultrashort Cu center dot center dot center dot Cu distances are observed. For the related complexes [(NHC)Cu-R'] no analogous complexes with bridging anionic ligands are realized. Instead; irrespective of the NHC ligand, linear coordinated copper complexes of different types are formed. Si-29 heteronriclear solution NMR spectroscopic data on.. [(NHC)Cu-I-SiR3] exhibit distinctly-different chemical shifts for the (in the solid state) monomeric and drineric-complexes suggesting different structure types also in solution. This agrees well with the observation of a trinuclear complex [(Me2IMe)Cu SnMe3](3) both in the solid state and in solution. Initial catalytic studies suggest that [(NHC)Cu-OtBu] complexes (NHC = ItBu, Me2IMe) are, in addition to the established [(IDipp)Cu OtBu] complex, efficient precatalysts for the silylation of Aldehydes and alpha,/beta-urisaturated ketones with pinB SiMe2Ph.