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Structural Studies of Macromolecules in Solution using Small Angle X-Ray Scattering
Published on: November 5, 2018
Investigating CN- cleavage by three-coordinate M[N(R)Ar]3 complexes
Gemma Christian1, Robert Stranger, Brian F Yates
1Department of Chemistry, Faculty of Science, Australian National University, Canberra, ACT 0200, Australia.
Dalton Transactions (Cambridge, England : 2003)
|April 17, 2008
Summary
Metal complexes bind cyanide but resist C-N bond cleavage due to unfavorable energetics and reduced metal-ligand backbonding. This explains why cyanide is not easily broken down in these systems, unlike dinitrogen.
Area of Science:
- Inorganic Chemistry
- Organometallic Chemistry
- Computational Chemistry
Background:
- Three-coordinate molybdenum complexes can bind cyanide, forming stable intermediates.
- Unlike dinitrogen (N2) analogues, the cyanide (CN-) ligand's carbon-nitrogen (C-N) bond remains intact in these molybdenum systems.
- Understanding the factors governing C-N bond cleavage is crucial for developing new catalytic processes.
Purpose of the Study:
- To investigate the energetic feasibility of C-N bond cleavage in metal-cyanide complexes.
- To explore the role of metal-ligand backbonding in the stability of cyanide intermediates.
- To computationally assess alternative metal centers (W, Re, Ta) for facilitating C-N bond cleavage.
Main Methods:
- Density Functional Theory (DFT) calculations were employed to model reaction pathways and energetics.
- Bond decomposition analysis was used to examine metal-ligand interactions and backbonding contributions.
- Calculations were performed on various model systems, including Mo, W, Re, and Ta complexes with cyanide.
Main Results:
- The final C-N bond cleavage step was found to be significantly endothermic in model Mo and W systems.
- Mixed-metal systems involving Re and W or Ta showed more favorable energetics but still did not facilitate facile C-N cleavage.
- Reduced metal-to-ligand pi-backbonding in cyanide complexes, compared to N2 or CO, contributes to the stability of the M-CN- interaction.
Conclusions:
- The inherent electronic structure of cyanide, including its negative charge and large metal-ligand orbital energy gap, hinders C-N bond cleavage.
- Strong metal-cyanide interactions further stabilize the intermediate, making cleavage energetically unfavorable.
- While alternative metal choices improve energetics, facile C-N bond cleavage in these specific systems remains challenging.
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