Density Functional Study on the Photopolymerization of Styrene Using Dinuclear Ru-Pd and Ir-Pd Complexes with...

Area of Science:

• Organometallic Chemistry
• Polymer Chemistry
• Computational Chemistry

Background:

• Dinuclear Ru-Pd and Ir-Pd complexes show enhanced photocatalytic reactivity in styrene polymerization under visible light.
• Catalyst structure significantly influences polymer yield and reactivity.
• Ir-Pd complexes with naphthyl substituents on phenyl ligands (Ir-Pd1) exhibit superior performance compared to isomers (Ir-Pd2).

Purpose of the Study:

• To investigate the mechanism behind the enhanced photocatalytic reactivity of dinuclear Ir-Pd complexes in styrene polymerization.
• To elucidate the role of excited state properties and electronic structure in catalyst performance.
• To computationally analyze the rate-determining step and intersystem crossing in the polymerization cycle.

Main Methods:

• Density functional theory (DFT) calculations were employed to study the electronic structure and reaction mechanisms.
• Calculation of radiative lifetimes of catalytic complexes to correlate with experimental observations.
• Estimation of singlet-triplet crossing points and intersystem crossing barrier heights for reaction intermediates.

Main Results:

• The Ir-Pd1 complex, featuring naphthyl substituents on phenyl ligands, demonstrated the longest radiative lifetime, consistent with experimental findings.
• Destabilization of the highest occupied molecular orbital (HOMO) via π*-π* interactions in Ir-Pd1 was identified as key to its enhanced reactivity.
• A smaller HOMO-lowest unoccupied molecular orbital (LUMO) energy gap in Ir-Pd1 facilitates metal-to-ligand charge transfer.
• Intersystem crossing barriers for the rate-determining step (second styrene insertion) were found to be significantly lower than thermal pathways.

Conclusions:

• The electronic structure and excited state stability, particularly the HOMO energy level influenced by ligand substituents, are crucial for the photocatalytic activity of Ir-Pd complexes.
• The calculated low intersystem crossing barriers explain the high efficiency of these catalysts in styrene polymerization under visible light irradiation.