Abnormal C5-Bound N-Heterocyclic Carbenes: Extremely Strong Electron Donor Ligands and Their Iridium(I) and Iridium(III) Complexes

摘要: Imidazolium salts are found to bind abnormally via C5 iridium(I) and iridium(III) give air-stable monodentate N-heterocyclic carbene complexes. Abnormal ligand binding was verified by X-ray diffraction in both Ir(I) Ir(III) In the case of Ir(I), it is necessary block C2 C4 positions form a stable sterically protected C5-bound complex. Infrared spectroscopy on carbonyl derivatives indicates that bound carbenes much stronger electron donors than their ubiquitous C2-bound counterparts. The Tolman electronic parameter for 1-isopropyl-2,4-diphenyl-3-methylimidazolin-5-ylidene 2039 cm-1, compared ca. 2050 cm-1 typical NHCs.