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Analysis of η 2 vs. η 5 Bonding of the Pentazolato Ligand to Manganese

Analysis of η 2 vs. η 5 Bonding of the Pentazolato Ligand to Manganese. Monika Wiedmann April 25, 2005. Introduction. Experimentally, the pentazolate anion is unknown. Pentazolate vs. Cyclopentadienyl Ion. Is it η 5 ?. Or is it η 2 ?. The Pentazolato Ligand on Mn. Calculations.

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Analysis of η 2 vs. η 5 Bonding of the Pentazolato Ligand to Manganese

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  1. Analysis of η2 vs. η5 Bonding of the Pentazolato Ligand to Manganese Monika Wiedmann April 25, 2005

  2. Introduction • Experimentally, the pentazolate anion is unknown.

  3. Pentazolate vs. Cyclopentadienyl Ion

  4. Is it η5? Or is it η2? The Pentazolato Ligand on Mn

  5. Calculations • Calculations were done on Mn(N5)(CO)3 with the pentazolato ligand in both the η5 and η2 orientations. • Geometry optimization and frequency calculations were performed at the RB3LYP 6-31+G(d) level. • Single point energy calculations were then run at the RB3LYP 6-311+G(3df) level. • NBO analysis was done to visualize the interactions between Mn and its ligands.

  6. Is it η5? Or is it η2? The Pentazolato Ligand on Mn 12 kcal/mol lower in energy

  7. Natural Bond Orbital Analysis • Regular quantum mechanical calculations result in delocalized molecular orbitals. • NBO takes these and transforms them into localized orbitals familiar to chemists (s, p, d, σ, σ*, π, π*). • Interactions between specific orbitals can be visualized.

  8. η2 Bonding of Pentazolate to Mn

  9. Occupied 3d Orbitals on Mn

  10. Unoccupied 3d and 4s Orbitals on Mn

  11. Nitrogen → Mn Electron Donation • Filled N-N σ bond donates electron density to unoccupied Mn 4s orbital.

  12. N: → Mn Donation

  13. η5 Bonding of Pentazolate to Mn

  14. Pentazolato → Mn Electron Donation

  15. N: → Mn Donation

  16. Mn → N Backbonding

  17. Bonding of C≡O to Mn

  18. O≡C: → Mn σ Donation

  19. Mn → C≡O Backbonding

  20. Conclusions • Manganese η2–pentazolato tricarbonyl is more stable than manganese η5–pentazolato tricarbonyl by 12 kcal/mol (in the gas phase). • The NBO program is useful for visualizing the interactions of various orbitals.

  21. Acknowledgments • Dr. Milletti (Eastern Michigan Univ.) • Dr. Schlegel • Dr. Winter • Barbara Munk • Elizabeth Rais

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