Abstract
IR spectroscopic and X-ray structural data of rhodium and palladium complexes of N-heterocyclic carbene (NHC) and 1H-pyridin-(2E)-ylidene (PYE) ligands indicate that both ligand classes exhibit similar electron-donating properties. However, catalytic application of palladium PYE complexes appears to be limited by PYE ligand loss. Density functional theory (DFT) calculations show that the Pd-C-NHC sigma-bond is very low-lying in energy (HOMO-14 and 15, ca. -11 eV) and a pi-backbonding contribution is also present, whereas the N-PYE sigma-bond is comparatively high-lying (HOMO-9 and 10, ca. -8 eV) and the highest occupied molecular orbital (HOMO) lowest unoccupied molecular orbital (LUMO) gap is also significantly less (4.0 vs. 5.6 eV). Essentially, electronegativity differences between Pd, C, and N render the Pd-N bond much more polarized and susceptible to electrophilic and nucleophilic attack and hence ligand substitution.
| Original language | English |
|---|---|
| Pages (from-to) | 1663-1671 |
| Number of pages | 9 |
| Journal | PURE AND APPLIED CHEMISTRY |
| Volume | 82 |
| Issue number | 8 |
| DOIs | |
| Publication status | Published - Aug 2010 |
Keywords
- density functional theory
- N-heterocyclic carbenes
- metal-ligand bonding
- 1H-pyridin-(2E)-ylidenes
- SUZUKI COUPLING REACTIONS
- MILD AEROBIC CONDITIONS
- MIXED AQUEOUS-MEDIUM
- ARYL BROMIDES
- COORDINATION CHEMISTRY
- CATALYTIC APPLICATION
- STRUCTURAL VARIATION
- PALLADIUM COMPLEXES
- ALKYLATION REACTION
- OXIDATIVE ADDITION