Redox and Luminescent Properties of Robust and Air-Stable N‑Heterocyclic Carbene Group 4 Metal Complexes

• Published in: Inorganic chemistry 2014-07, Vol.53 (14), p.7371-7376
• Main Authors: Romain, Charles, Choua, Sylvie, Collin, Jean-Paul, Heinrich, Martine, Bailly, Corinne, Karmazin-Brelot, Lydia, Bellemin-Laponnaz, Stéphane, Dagorne, Samuel
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Electron Spin Resonance Spectroscopy; Heterocyclic Compounds - chemistry; Inorganic chemistry; Luminescence; Magnetic Resonance Spectroscopy; Metals - chemistry; Methane - analogs & derivatives; Methane - chemistry; Oxidation-Reduction
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic500718y

Robust and air-stable homoleptic group 4 complexes of the type M(L)2 [1–3; M = Ti, Zr, Hf; L = dianionic bis(aryloxide) N-heterocyclic carbene (NHC) ligand] were readily synthesized from the NHC proligand 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)imidazolinium chloride (H 3 L,Cl) and appropriate group 4 precursors. As deduced from cyclic voltammetry studies, the homoleptic bis-adduct zirconium and hafnium complexes 2 and 3 can also be oxidized, with up to four one-electron-oxidation signals for the zirconium derivative 2 (three reversible signals). Electron paramagnetic resonance data for the one-electron oxidation of complexes 1–3 agree with the formation of ligand-centered species. Compounds 2 and 3 are luminescent upon excitation in the absorption band at 362 nm with emissions at 485 and 534 nm with good quantum yields (ϕ = 0.08 and 0.12) for 2 and 3, respectively. In contrast, the titanium complex 1 does not exhibit luminescent properties upon excitation in the absorption band at 310 and 395 nm. Complexes 2 and 3 constitute the first examples of emissive nonmetallocene group 4 metal complexes.