Semiautomated Transition State Localization for Organometallic Complexes with Semiempirical Quantum Chemical Methods.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Reaction Mechanism Studies

Background:

• Transition state localization is crucial for understanding reaction mechanisms.
• Traditional methods relying on chemical intuition can be error-prone for complex systems.
• Semiempirical methods offer a balance between accuracy and computational cost.

Purpose of the Study:

• To present an efficient computational protocol for robust transition state localization.
• To demonstrate the capabilities of GFNn-xTB methods combined with the mGSM algorithm.
• To compare the performance of GFNn-xTB with established semiempirical methods (PM6-D3H4, PM7).

Main Methods:

• Utilized extended tight-binding semiempirical methods (GFNn-xTB).
• Employed a state-of-the-art transition state localization algorithm (mGSM).
• Tested the protocol on a modified MOBH35 benchmark set of 29 organometallic reactions.

Main Results:

• GFNn-xTB methods achieved significantly higher success rates (89.7% for GFN1-xTB, 86.2% for GFN2-xTB) compared to PM6-D3H4 (72.4%) and PM7 (69.0%).
• GFNn-xTB methods computed barrier heights and reaction energies with improved accuracy and reduced computational cost.
• The mean error for barrier heights using GFN2-xTB (8.2 kcal mol^-1) is comparable to low-cost DFT methods.

Conclusions:

• The GFNn-xTB and mGSM combination provides an efficient and robust protocol for transition state localization in complex reactions.
• This approach surpasses traditional semiempirical methods in accuracy and success rate.
• Enables semiquantitative assessment of reaction pathways at a reduced computational cost.