N-heterocyclic carbene complexes of copper(i) thiocyanate: synthesis and structural characterization

The synthesis and characterization of three N-heterocyclic carbene (NHC) complexes of copper(I) thiocyanate [Cu(IMes)(NCS)]₂ (1), [Cu(IXy)(NCS)]₂ (2), and [Cu(IPr)(NCS)] (3) [IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, IXy = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] are described. Single crystal diffraction and IR spectroscopy shows that reaction of one equivalent of sodium thiocyanate with [Cu(NHC)Cl] results in the formation of solid-state centrosymmetric dimers for 1 and 2 with bridging thiocyanate ligands bound through both N and S. In contrast, the equivalent reaction with IPr gives a monomeric species with N bound thiocyanate. In the solution state, all the structures of complexes 1-3 would appear to be monomeric, as evidenced by both solution state FT-IR and ¹³C NMR spectroscopic studies. In addition the precursor to complex 2 [Cu(IXy)Cl] (4) was structurally characterized by X-ray diffraction revealing a one-dimensional chain structure that propagates through C-H···Cl intermolecular interactions with both methyl and aromatic hydrogen atoms.