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γ-Agostic interactions in (MesCCC)Fe-Mes(L) complexes.

Daniel C Najera1, Marconi N Peñas-Defrutos2,3, Max García-Melchor2

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Iron compounds with a bis(NHC) pincer ligand show agostic interactions in the mesityl group. The type of L-ligand affects interaction strength, confirmed by NMR and DFT calculations.

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Area of Science:

  • Organometallic Chemistry
  • Coordination Chemistry
  • Computational Chemistry

Background:

  • Agostic interactions, a three-center, two-electron interaction between a metal and a C-H bond, are crucial in organometallic chemistry.
  • Bis(NHC) pincer ligands offer unique coordination environments for metal centers.
  • Iron complexes are versatile catalysts and model systems in inorganic chemistry.

Purpose of the Study:

  • To investigate agostic interactions in iron complexes featuring a bis(NHC) pincer CCC ligand.
  • To determine the influence of ancillary L-type ligands on the strength of these agostic interactions.
  • To rationalize observed trends and explore the predictive power of computational methods.

Main Methods:

  • Synthesis and characterization of iron(II) complexes with a CCC pincer ligand and varying L-type ligands.
  • Nuclear Magnetic Resonance (NMR) spectroscopy, specifically 1H NMR, to probe the electronic environment of the mesityl group.
  • Density Functional Theory (DFT) calculations to model the electronic structure and bonding.

Main Results:

  • Agostic interactions were definitively observed in the bound mesityl group of the iron complexes.
  • The strength of the agostic interaction was modulated by the nature of the L-type ligand.
  • NMR data showed a clear upfield shift in mesityl methyl resonances correlating with ligand variation.
  • DFT calculations successfully rationalized experimental observations and predicted trends.

Conclusions:

  • The study confirms the presence and tunability of agostic interactions in this iron pincer complex system.
  • Ancillary ligand choice is a key factor in modulating C-H---metal interactions.
  • DFT calculations serve as a reliable tool for understanding and predicting agostic behavior in related systems.