1H and 19F PGSE diffusion studies on iridium PHOX complexes: counterion and solvent dependences

Area of Science:

• Organometallic Chemistry
• Supramolecular Chemistry
• Physical Chemistry

Background:

• Cationic iridium complexes with chiral P,N-auxiliaries are important in catalysis.
• Understanding ion-pairing is crucial for predicting complex behavior in solution.
• Solvent polarity and anion structure significantly influence ion-pairing dynamics.

Purpose of the Study:

• To investigate the ion-pairing behavior of cationic iridium complexes.
• To determine the influence of different anions and solvents on cation diffusion.
• To elucidate the relationship between ion-pairing and the mobility of iridium complexes.

Main Methods:

• Pulsed gradient spin-echo (PGSE) diffusion measurements using 1H and 19F NMR.
• Studies conducted on mono- and trinuclear iridium complexes with PHOX auxiliary.
• Analysis of complexes with various anions (BF4-, PF6-, OTf-, B(C6F5)4-, BArF-) in different solvents (methanol, chloroform, dichloromethane, 1,2-dichloroethane).

Main Results:

• In chloroform, strong ion-pairing was observed between cations and all anions.
• In methanol, cations moved independently of anions, indicating no ion-pairing.
• In dichloromethane and 1,2-dichloroethane, smaller anions showed minimal impact, while larger boron-based anions hindered cation diffusion, suggesting partial ion-pairing.

Conclusions:

• Ion-pairing in cationic iridium complexes is highly dependent on solvent polarity and anion size.
• Methanol promotes dissociation, while chloroform promotes strong ion-pairing.
• Larger, weakly coordinating anions exhibit partial ion-pairing in less polar solvents, affecting cation mobility.