Bonding Analysis of N‐Heterocyclic Carbene Tautomers and Phosphine Ligands in Transition‐Metal Complexes: A Theoretical Study |
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Authors: | Ralf Tonner Greta Heydenrych Dr Gernot Frenking Prof?Dr |
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Institution: | Fachbereich Chemie, Philipps‐Universit?t Marburg, Hans‐Meerwein‐Strasse, D‐35032 Marburg, Germany, Fax: (+49)?6421‐282‐5566 |
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Abstract: | DFT calculations at the BP86/TZ2P level were carried out to analyze quantitatively the metal–ligand bonding in transition‐metal complexes that contain imidazole (IMID), imidazol‐2‐ylidene (nNHC), or imidazol‐4‐ylidene (aNHC). The calculated complexes are Cl4TM(L)] (TM=Ti, Zr, Hf), (CO)5TM(L)] (TM=Cr, Mo, W), (CO)4TM(L)] (TM=Fe, Ru, Os), and ClTM(L)] (TM=Cu, Ag, Au). The relative energies of the free ligands increase in the order IMID<nNHC<aNHC. The energy levels of the carbon σ lone‐pair orbitals suggest the trend aNHC>nNHC>IMID for the donor strength, which is in agreement with the progression of the metal–ligand bond‐dissociation energy (BDE) for the three ligands for all metals of Groups 4, 6, 8, and 10. The electrostatic attraction can also be decisive in determining trends in ligand–metal bond strength. The comparison of the results of energy decomposition analysis for the Group 6 complexes (CO)5TM(L)] (L=nNHC, aNHC, IMID) with phosphine complexes (L=PMe3 and PCl3) shows that the phosphine ligands are weaker σ donors and better π acceptors than the NHC tautomers nNHC, aNHC, and IMID. |
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Keywords: | carbenes bonding analysis density functional calculations N‐heterocyclic carbenes phosphine complexes |
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