The Pauli Repulsion-Lowering Concept in Catalysis.

Area of Science:

• Organic Chemistry
• Quantum Mechanics
• Catalysis

Background:

• Organic compounds are vital in pharmaceuticals, plastics, fuels, and more, with catalysts essential for efficient synthesis.
• Current understanding often relies on Frontier Molecular Orbital (FMO) theory, specifically LUMO-lowering catalysis, to explain catalyst function.
• The LUMO-lowering concept, while popular, has limitations and is not always the operative factor in catalyzed reactions.

Purpose of the Study:

• To propose a unified, quantum mechanics-rooted framework for understanding and predicting chemical reactivity in catalysis.
• To introduce and validate the concept of Pauli repulsion-lowering catalysis as a more fundamental explanation.
• To demonstrate the general applicability of this new model across different reaction types and catalyst interactions.

Main Methods:

• Utilized state-of-the-art computational methods, including the Activation Strain Model (ASM).
• Employed quantitative Kohn-Sham molecular orbital (KS-MO) theory and Energy Decomposition Analysis (EDA).
• Analyzed the catalyst-substrate interactions, focusing on orbital overlaps and Pauli repulsion.

Main Results:

• Catalyst binding not only stabilizes the substrate's LUMO but significantly reduces Pauli repulsion between key reactant orbitals.
• This repulsion reduction occurs via catalyst-induced polarization of occupied orbitals, decreasing overlap between reactants.
• The Pauli repulsion-lowering mechanism was confirmed for Diels-Alder and Michael addition reactions, irrespective of catalyst bonding type.

Conclusions:

• Pauli repulsion-lowering provides a more accurate and unified explanation for catalytic acceleration than LUMO-lowering.
• This mechanism is the fundamental physical factor responsible for speeding up catalyzed organic reactions.
• The findings offer guidance for designing more efficient catalytic transformations in future experimental research.