Synthesis and Characterization of a Copper Complex Supported by a Z-type Sb ^V Ligand: XPS and DFT Study of Electronic Structure

We describe the synthesis and characterization of a Cu-(I) complex, {Q₃Sb-(<i>o</i>-chlor)}-Cu-(OTf) (Q = 8-quinolinyl; OTf = trifluoromethanesulfonate; <i>o</i>-chlor = <i>o</i>-choranil), supported by the Sb-(V) ligand Q₃Sb-(<i>o</i>-chlor). The complex {Q₃Sb-(<i>o</i>-chlor)}-Cu-(OTf) was experimentally characterized via ¹H, ¹³C-{¹H}, and ¹⁹F-{¹H} NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) as well as examined computationally with density functional theory (DFT) calculations. Variable temperature ¹H NMR spectroscopy (20 to -110 °C) indicates temperature-dependent fluxional processes for {Q₃Sb-(<i>o</i>-chlor)}-Cu-(OTf) and uncoordinated Q₃Sb-(<i>o</i>-chlor). The electron density of Cu for {Q₃Sb-(<i>o</i>-chlor)}-Cu-(OTf) was probed by comparing Cu^II/Cu^I redox potential and Cu 2p electron binding energies, using XPS, with a related non-Sb-containing complex, (TMQA)-Cu-(OTf) (TMQA = tris-(quinolin-2-ylmethyl)-amine). The <i>E</i> _1/2 of the Cu^II/Cu^I redox of {Q₃Sb-(<i>o</i>-chlor)}-Cu-(OTf) is shifted 670 mV more positive than that of (TMQA)-Cu-(OTf). XPS spectra of {Q₃Sb-(<i>o</i>-chlor)}-Cu-(OTf) and (TMQA)-Cu-(OTf) indicate a 0.8 eV higher Cu 2p binding energy for {Q₃Sb-(<i>o</i>-chlor)}-Cu-(OTf). Computational studies of the molecular orbitals and localized natural bonding orbitals (NBOs) are consistent with a weak Cu-(I) → Sb-(V) interaction for {Q₃Sb-(<i>o</i>-chlor)}-Cu-(OTf), for which Sb-(V) acts as a Z-type ligand.