Bulky Terphenyl Phosphines Stabilize Otherwise Highly Reactive Iridium Fragments, Key in C-H Activation Reactions

Area of Science:

• Organometallic Chemistry
• Catalysis
• C-H Activation

Background:

• Iridium complexes with pentamethylcyclopentadienyl (Cp*) ligands are key in C-H bond activation.
• The influence of sterically demanding phosphine ligands on these iridium systems remains underexplored.

Purpose of the Study:

• To synthesize and characterize iridium complexes featuring bulky terphenyl phosphine ligands.
• To investigate the impact of steric bulk on the reactivity and stability of iridium(I) and iridium(III) species.
• To explore the potential of these novel complexes in selective C-H activation reactions.

Main Methods:

• Synthesis and structural characterization of novel iridium(I) complexes with terphenyl phosphine ligands.
• Reactivity studies using methyl triflate to probe oxidative addition.
• Computational studies to rationalize observed reactivity differences.
• Exploration of further chemical transformations of the activated iridium(III) complex.

Main Results:

• Two stable iridium(I) complexes, [Cp*Ir(PMe2ArDtbp2)] and [Cp*Ir(PMe2ArDipp2)], were synthesized and structurally characterized.
• These complexes exhibit strong metal-arene interactions, conferring unusual stability.
• Only the [Cp*Ir(PMe2ArDtbp2)] complex underwent clean oxidative addition with methyl triflate, forming the cationic methyl complex [Cp*IrMe(PMe2ArDtbp2)]+.
• Computational analysis revealed steric effects beyond conventional metrics influencing the divergent reactivity.
• The cationic iridium(III) complex showed versatile reactivity, including intramolecular C-H activation and intermolecular functionalization of 1,2-difluorobenzene.

Conclusions:

• Terphenyl phosphine ligands effectively stabilize reactive iridium fragments.
• Steric congestion plays a crucial role in dictating the reactivity of iridium complexes in C-H activation.
• These findings open avenues for developing sterically demanding catalysts for selective C-H functionalization.