Molecular Motion in the Interconverting σ-H₂, Di-, and Tri-hydride Regimes:

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Chemical Dynamics

Background:

• The transition-metal complex [math] serves as a model for studying interconversion between dihydrogen and dihydride isomers.
• Understanding the structural dynamics and isomerization pathways is crucial for predicting reactivity and stability.

Purpose of the Study:

• To directly assess the motion and isomerization of dihydrogen/dihydride moieties in [math] using advanced computational methods.
• To investigate the influence of temperature on the complex's isomeric landscape and dynamics.

Main Methods:

• Ab initio molecular dynamics (AIMD) simulations were employed.
• Enhanced sampling techniques were utilized to explore conformational space.
• Simulations were performed at 298 K and higher temperatures.

Main Results:

• At 298 K, ligand rotations (H2 and phosphine) dominate, with no significant population of dihydride forms observed in classical thermodynamics.
• Fleeting configurations outside the sigma-H2 structure were noted in unrestrained AIMD.
• Higher temperatures revealed energetically competitive tri-hydride isomers, alongside sigma-H2 and cis-/trans-dihydride forms.

Conclusions:

• The complex displays remarkable isomeric flexibility, with low-energy pathways for hydrogen/hydride transfer and phosphine dissociation.
• The discovery of tri-hydride isomers significantly expands the known isomeric landscape of this model system.
• Computational simulations provide critical insights into the dynamic behavior and diverse structures accessible to transition-metal complexes.