Unveiling the Unusual Mn(CO)₃ Migration in a Manganese Cyclohexenyl Complex by DFT Computations

Area of Science:

• Organometallic Chemistry
• Homogeneous Catalysis
• Computational Chemistry

Background:

• Transition metal agostic interactions (TM…H…C) are crucial for C-H bond activation in homogeneous catalysis.
• Manganese complexes offer unique reactivity profiles, but the mechanisms of fragment migration remain underexplored.
• Understanding these mechanisms is key to designing novel catalytic systems.

Purpose of the Study:

• To investigate the role of manganese agostic intermediates in the migration of the Mn(CO)3 fragment.
• To elucidate the mechanism of protonation-induced transformation of (exo-phenyl)(η3-cyclohexenyl)manganese tricarbonyl.
• To characterize the agostic interactions involved using computational methods.

Main Methods:

• Comprehensive density functional theory (DFT) calculations were employed.
• Geometry optimizations and transition state searches were performed.
• Atoms-In-Molecules (AIM) and Natural Adaptive Orbitals (NAdOs) analyses were used to characterize agostic interactions.

Main Results:

• The migration of the Mn(CO)3 fragment proceeds via a series of mono-agostic and di-agostic intermediates.
• The formation of a di-agostic (η2-phenyl)manganese complex is identified as the rate-limiting step (15.4 kcal mol-1 Gibbs barrier).
• Agostic interactions were successfully characterized, providing insights into the reaction pathway.

Conclusions:

• The study successfully explains the experimental observations of unusual Mn(CO)3 fragment migration.
• Di-agostic intermediates play a critical role in the catalytic cycle.
• The findings highlight the significance of TM…H…C agostic interactions in manganese-catalyzed reactions, opening new avenues for catalyst design.