Dative and electron-sharing bonding in transition metal compounds.

Area of Science:

• Inorganic Chemistry
• Quantum Chemistry
• Computational Chemistry

Background:

• Transition metal (TM) compounds with various ligands are crucial in catalysis and synthesis.
• Understanding the nature of TM-ligand bonds, whether dative or electron-sharing, is key to predicting reactivity.
• Previous classifications of TM-ligand bonds relied on simplified models.

Purpose of the Study:

• To investigate the bonding in high and low oxidation state transition metal compounds with carbene, carbyne, alkene, and alkyne ligands.
• To differentiate between dative and electron-sharing bonding models using advanced computational methods.
• To analyze the influence of fragment electronic states (singlet vs. triplet, closed-shell vs. open-shell) on orbital interactions.

Main Methods:

• Density Functional Theory (DFT) calculations at the BP86-D3(BJ)/def2-TZVPP level.
• Energy Decomposition Analysis - Natural Orbitals for Chemical Valence (EDA-NOCV) for detailed bond analysis.
• Comparison of orbital interactions using closed-shell (singlet) and open-shell (triplet) fragments.

Main Results:

• Fischer-type carbene complexes show significantly lower orbital interaction (ΔE_orb) with singlet fragments compared to triplet fragments.
• Schrock-type carbene complexes exhibit similar ΔE_orb values for both singlet and triplet fragments.
• Fischer-type carbyne complexes are best described by neutral doublet fragments, involving σ donation, π backdonation, and a π electron-sharing bond.
• Schrock-type carbynes and metallacyclic species are better described using singlet fragments, with distinctions blurring for metallacycles.

Conclusions:

• The electronic state of fragments significantly impacts the bonding description of transition metal complexes.
• A nuanced understanding of bonding, beyond simple dative or electron-sharing classifications, is necessary.
• EDA-NOCV provides valuable insights into the intricate nature of transition metal-ligand interactions.