Hidden aryl-exchange processes in stable 16e Rh^III [RhCp*Ar₂] complexes, and their unexpected transmetalation...

Area of Science:

• Organometallic Chemistry
• Catalysis
• Reaction Mechanisms

Background:

• Stable 16-electron, 5-coordinate rhodium complexes of the type [RhCp*Ar2] were synthesized and studied.
• Aryl transmetalation reactions are crucial in organometallic chemistry but can be slow.
• The electronic and coordination properties of metal complexes influence their reactivity.

Purpose of the Study:

• To investigate the reactivity of 16-electron 5-coordinate rhodium complexes in aryl transmetalation reactions.
• To elucidate the mechanism of these transmetalation processes.
• To identify potential catalysts or factors accelerating these exchanges.

Main Methods:

• Synthesis and characterization of 16-electron 5-coordinate rhodium complexes ([RhCp*Ar2]).
• Experimental investigation of aryl transmetalation reactions involving these complexes.
• Computational studies to support mechanistic hypotheses.
• Identification of catalytic species and mechanistic intermediates.

Main Results:

• Fast aryl transmetalations were observed for the [RhCp*Ar2] complexes.
• These transmetalations were found to be catalyzed by minute quantities of an 18-electron rhodium dimer, (μ-OH)2[RhCp*Ar]2.
• The catalytic species generates a 16-electron [RhCp*Ar(OH)] intermediate.
• Computational studies confirmed the non-spontaneous nature of the exchange and the catalytic role of the dimer.

Conclusions:

• Minute amounts of a rhodium hydroxide dimer act as an efficient catalyst for aryl transmetalation reactions.
• The hydroxide ligand plays a critical role by bridging and significantly reducing the activation barrier.
• This discovery offers new insights into catalytic cycles involving rhodium complexes and hydroxide ligands.