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Towards the rational design of palladium-N-heterocyclic carbene catalysts by a combined experimental and computational approach |
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| Authors: | Christopher J. O'Brien Gregory A. Chass Alan C. Hopkinson David H. Setiadi De-Cai Fang |
| Affiliation: | a Department of Chemistry, York University, 4700 Keele Street, Toronto, ON, Canada M3J 1P3 b GIOCOMMS, 2-158 Major Street, Toronto, ON, Canada M5S 2K2 c Department of Chemistry, McMaster University, 280 Main Street West, Hamilton, ON, Canada L8S 4A1 d Department of Chemistry, Beijing Normal University, Beijing, China 100875 |
| Abstract: | A combined experimental and computational approach towards the development of Pd-NHC catalysts is described. A range of benzimidazolylidinium ligands incorporating electron-rich and electron-poor substituents were prepared and evaluated in the Suzuki reaction. The most electron-rich ligand showed the highest catalytic activity. Based on this information, the first alkyl-alkyl Negishi cross-coupling reaction protocol was developed. Evaluation of N,N′-diaryl-(4,5-dihydro)imidazolylilidinium ligands showed a strong dependence on the steric topography around the metal centre. A computational study of the most active ligand in the Negishi reaction, its Pd(0) and PdCl2-complexes and related structures were modelled at the B3LYP/DZVP and HF/3-21G levels of theory. The potential energy hypersurfaces flattened with increase in ligand size. Binding energies were computed for carbene/Pd(0) adducts (in the range ∼31-40 kcal mol−1), roughly double that for PH3 (∼16 kcal mol−1). Weak intramolecular interactions were found using AIM analyses. |
| Keywords: | Alkyl-alkyl Negishi cross-coupling reaction Oxidative addition Reductive elimination |
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