Sulfur-Containing Analogues of the Reactive [CuOH]²⁺ Core

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Computational Chemistry

Background:

• The reactivity of copper-oxygen (LCuOH) complexes is well-established.
• Understanding the electronic and structural properties of related copper-sulfur (LCuSR) complexes is crucial for comparative analysis.
• Previous studies have suggested variations in electronic structure for different ligand types in copper complexes.

Purpose of the Study:

• To synthesize and characterize copper-sulfur complexes ([Bu4N][LCuSR], R = H, Ph) for comparison with LCuOH.
• To investigate the redox potentials and proton-coupled electron transfer (PCET) reactivity of LCuSR complexes.
• To elucidate the electronic structure of LCuZ complexes (Z = OH, SH, SPh, F, Cl, Br) using advanced computational methods.

Main Methods:

• Synthesis and characterization of [Bu4N][LCuSR] complexes via spectroscopy and X-ray crystallography.
• Electrochemical studies to determine redox potentials (LCuSR-/0 vs LCuOH-/0).
• Kinetic studies of PCET reactions at low temperatures (-80 °C).
• Density Functional Theory (DFT) and time-dependent DFT calculations.
• Complete Active Space (CAS) self-consistent field and localized orbital CAS configuration interaction calculations.

Main Results:

• LCuSR complexes were successfully prepared and characterized.
• Redox potentials for LCuSR-/0 were approximately 50 mV lower than for LCuOH-/0, consistent with sulfur's lower electronegativity.
• PCET reaction rates for LCuSR were over 100 times slower than for LCuOH.
• Computational analyses revealed subtle structural and UV-visible differences between LCuOH, LCuSH, and LCuSPh.
• Calculations across a series of LCuZ complexes (Z = F, Cl, Br) support a consistent electronic structure.

Conclusions:

• Copper-sulfur complexes exhibit distinct electrochemical and reactivity profiles compared to copper-oxygen analogues.
• The electronic structure of the LCuZ series is consistent, challenging previous interpretations of ligand field effects.
• This work provides a unified understanding of electronic structures across various copper complexes with different chalcogenide and halide ligands.