Modulation of Isomerization and Ligand Exchange Rates by π Bonding in Bis(iminoxolene)iridium Pyridine Complexes

Area of Science:

• Organometallic Chemistry
• Photochemistry
• Inorganic Chemistry

Background:

• Iridium complexes with iminoxolene ligands are investigated for their unique electronic and structural properties.
• Understanding isomerism and reactivity in these complexes is crucial for developing new catalytic and photophysical applications.

Purpose of the Study:

• To investigate the formation, electronic structure, and reactivity of cis and trans isomers of bis(iminoxolene)iridium complexes.
• To elucidate the factors governing the trans-cis isomerization and pyridine ligand dissociation.

Main Methods:

• Synthesis and characterization of bis(iminoxolene)iridium complexes.
• Spectroscopic analysis (UV-Vis, NMR) and variable-temperature NMR.
• Density functional theory (DFT) calculations.
• Kinetic studies of ligand dissociation and isomerization.

Main Results:

• The bis(iminoxolene)iridium complex forms both kinetic (trans) and thermodynamic (cis) isomers with pyridine.
• Electronic structures of cis and trans isomers are similar, featuring iminoxolene-centered HOMO and metal-iminoxolene π* LUMO.
• The cis isomers exhibit unusually low-energy triplet states due to altered iminoxolene dihedral angles.
• The trans isomer undergoes significantly faster pyridine dissociation (10^8 times) due to steric hindrance and electronic effects.

Conclusions:

• Stereoelectronic effects and steric interactions play a critical role in the stability and reactivity of iminoxolene-iridium complexes.
• The observed differences in pyridine dissociation rates are attributed to ligand-ligand and ligand-metal interactions.
• The study provides insights into the design principles for tuning the properties of organometallic complexes.