Organic Azide and Auxiliary-Ligand-Free Complexes of Coinage Metals Supported by N-Heterocyclic Carbenes

Organic azide complexes of copper(I) and silver(I), [(SIPr)CuN(1-Ad)NN][SbF6], [(SIPr)CuN(2-Ad)NN][SbF6], [(SIPr)CuN(Cy)NN][SbF6], and [(SIPr)AgN(1-Ad)NN][SbF6] have been synthesized by using Ag[SbF6] and the corresponding organic azides with (SIPr)CuBr and (SIPr)AgCl (SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene). The copper and silver organic azide complexes were characterized by various spectroscopic techniques and X-ray crystallography. Group trends of isoleptic Cu(I), Ag(I), and Au(I) organic azide complexes are presented on the basis of experimental data and a detailed computational study. The νasym(N3) values of the metal-bound 1-AdNNN in [(SIPr)MN(1-Ad)NN]+follow the order Ag < Cu < Au. DFT calculations show that gold(I) forms the strongest bond with 1-AdNNN in this series, while silver has the weakest interaction. Furthermore, auxiliary ligand free coinage metal N-heterocyclic carbene complexes, [(SIPr)M][SbF6], have been synthesized via metathesis reactions of (SIPr)MCl (M = Cu, Ag, Au) with Ag[SbF6]. X-ray crystal structures of dinuclear [(SIPr)Ag]2[SbF6]2and [(SIPr)Au]2[SbF6]2are also reported. They show close metallophilic contacts. [(SIPr)Au]2[SbF6]2reacts with OEt2, SMe2, and CNtBu to afford [(SIPr)Au(OEt2)][SbF6], [(SIPr)Au(SMe2)][SbF6], and [(SIPr)Au(CNtBu)][SbF6] adducts, respectively.