Solution-Phase Conformational/Vibrational Anharmonicity in Comonomer Incorporation Polyolefin Catalysis.

Area of Science:

• Catalysis
• Polymer Chemistry
• Computational Chemistry

Background:

• Accurate prediction of comonomer incorporation in polyolefin catalysis requires precise free energy calculations.
• Experimental free energies often necessitate sub-kcal/mol resolution.
• Constrained geometry complexes serve as model systems for ethene and α-olefin incorporation.

Purpose of the Study:

• To characterize the solution-phase insertion barrier using advanced computational methods.
• To analyze the contributions of conformational and vibrational anharmonicity to the insertion barrier.
• To improve the quantitative prediction of comonomer incorporation statistics in polyolefin catalysis.

Main Methods:

• Quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations (over 6 ns).
• Zero-temperature string method for barrier characterization.
• Analysis of conformational and vibrational anharmonicity in vacuum and solution.

Main Results:

• Solution-phase conformational sampling introduces 0-2 kcal/mol corrections to the insertion barrier.
• These corrections are on the scale needed to resolve experimental free energies.
• Anharmonic contributions from solution-phase sampling are critical and often omitted in static calculations.

Conclusions:

• Accurate calculation of anharmonic contributions from conformational sampling in solution is essential.
• This approach is a key step toward quantitatively predicting comonomer incorporation statistics.
• Advanced QM/MM simulations offer crucial insights beyond static DFT and implicit solvation models.