Quantum Hydrogen Tunneling in an Iridium Dihydride Complex

Area of Science:

• Organometallic Chemistry
• Quantum Mechanics
• Spectroscopy

Background:

• Quantum mechanical tunneling (QMT) is a fundamental quantum phenomenon where particles can traverse potential energy barriers.
• QMT plays a role in various chemical reactions, particularly those involving hydrogen transfer.
• Metal dihydride complexes are important in catalysis and mechanistic studies.

Purpose of the Study:

• To investigate the mechanism of hydrogen exchange in a novel iridium dihydride complex.
• To confirm the structural and electronic properties of the iridium complex.
• To explore the reactivity of the iridium dihydride complex.

Main Methods:

• Variable temperature Nuclear Magnetic Resonance (NMR) spectroscopy to study H-H exchange coupling constants (J_H-H).
• Deuterium labeling (IrHD) to probe the nature of the coupling.
• Relaxation rate measurements (T1,min) to distinguish between dihydride and dihydrogen complexes.
• X-ray photoelectron spectroscopy (XPS) and computational studies to determine oxidation state and electronic structure.

Main Results:

• Observed significant, temperature-dependent H-H exchange coupling (J_H-H = 99-162 Hz) via QMT in the iridium dihydride complex.
• Demonstrated nonlinear Arrhenius behavior for the exchanging hydrogens and absence of detectable J_H-D coupling.
• High relaxation rates (T1,min = 0.250-0.262 s) support a metal dihydride structure, ruling out significant classical scalar coupling.
• Reactivity studies, XPS, and computational analysis indicate the iridium complex is in the formal +III oxidation state.

Conclusions:

• The study provides compelling evidence for quantum mechanical tunneling driving H-H exchange coupling in a metal dihydride complex.
• The findings confirm the complex as a metal dihydride with iridium in the +III oxidation state.
• This work highlights the importance of QMT in understanding reactivity and mechanisms in organometallic chemistry.