A molecular mechanical model for N-heterocyclic carbenes

Area of Science:

• Computational Chemistry
• Organic Chemistry
• Molecular Modeling

Background:

• N-heterocyclic carbenes (NHCs) are versatile compounds with significant synthetic utility.
• Accurate molecular simulations of NHCs are crucial for understanding their reactivity and properties.
• Existing force fields may not adequately capture the unique electronic and steric features of NHCs.

Purpose of the Study:

• To develop and validate a robust set of force fields for nine synthetically relevant N-heterocyclic carbenes.
• To enable large-scale molecular simulations of NHCs by creating force fields compatible with established simulation packages.

Main Methods:

• Ab initio geometry optimizations were used to calculate bonding parameters for NHCs.
• Non-bonding interactions were fitted using a water molecule as a probe, sampling interaction energies through the lone pair and π system.
• Coupled-cluster with singles, doubles, and perturbative triples (CCSD(T))/complete basis set (CBS) calculations provided reference interaction energies.
• An additional Coulombic interaction site was incorporated to represent the lone pair's directional influence.

Main Results:

• The developed Carbene Force Field (CaFF) demonstrated robust performance across different probe molecules (water, methanol).
• CaFF models showed minimal deviation in potential energies when using varied molecular mechanical models.
• The force fields are designed for seamless integration with standard OPLS and AMBER force fields.

Conclusions:

• The CaFF models provide a reliable method for simulating a wide range of N-heterocyclic carbenes.
• This development significantly expands the accessibility of molecular simulations for NHC research.
• The compatibility with existing force fields facilitates broader application in computational studies.