Isolable acetylene complexes of copper and silver

Copper and silver play important roles in acetylene transformations but isolable molecules with acetylene bonded to Cu(I) and Ag(I) ions are scarce. This report describes the stabilization of pi-acetylene complexes of such metal ions supported by fluorinated and non-fluorinated, pyrazole-based chelators. These Cu(I) and Ag(I) complexes were formed readily in solutions under an atmosphere of excess acetylene and the appropriate ligand supported metal precursor, and could be isolated as crystalline solids, enabling complete characterization using multiple tools including X-ray crystallography. Molecules that display kappa(2)- or kappa(3)-ligand coordination modes and trigonal planar or tetrahedral metal centers have been observed. Different trends in coordination shifts of the acetylenic carbon resonance were revealed by C-13 NMR spectroscopy for the Cu(I) and Ag(I) complexes. The reduction in acetylene (nu) over bar (C C) due to metal ion coordination is relatively large for copper adducts. Computational tools were also used to quantitatively understand in detail the bonding situation in these species. It is found that the interaction between the transition metal fragment and the acetylene ligand is significantly stronger in the copper complexes, which is consistent with the experimental findings. The C C distance of these copper and silver acetylene complexes resulting from routine X-ray models suffers due to incomplete deconvolution of thermal smearing and anisotropy of the electron density in acetylene, and is shorter than expected. A method to estimate the C C distance of these metal complexes based on their experimental (nu) over bar (C C) is also presented.

Automated summary

This report describes the stabilization of Cu(I) and Ag(I) pi-acetylene complexes supported by fluorinated and non-fluorinated, pyrazole-based chelators. These complexes were formed easily in solutions and could be isolated as crystalline solids. Different coordination modes and metal centers were observed, and the coordination shifts of acetylenic carbon resonance were revealed by C-13 NMR spectroscopy. The bonding between the transition metal fragment and the acetylene ligand was found to be stronger in the copper complexes. The C C distance of these complexes was shorter than expected due to incomplete deconvolution of thermal smearing and electron density anisotropy in acetylene.