Helically Chiral NHC‐Gold(I) Complexes: Synthesis, Chiroptical Properties and Electronic Features of the [5]Helicene‐Imidazolylidene Ligand

Abstract

We describe the preparation of helically chiral gold(I) complexes bearing a [5]helicenic‐N‐heterocyclic carbene ligand. They were successfully obtained as enantiopure compounds by semi‐preparative chiral HPLC and their structural, chiroptical, and photophysical properties were subsequently investigated. Notably, strong electronic circular dichroism, dual emission from singlet and triplet states, with the timescale of the latter up to the millisecond range at room temperature, and moderate circularly phosphorescence were observed. The σ‐donating and π‐accepting properties of the constituent helical ortho‐fused π‐conjugated carbene were investigated by classical quantitative analysis of the IR stretching frequencies and NMR characteristics of the corresponding Ir(CO)2Cl complex and selenourea.

Helicenic N-heterocyclic carbene copper(i) complex displaying circularly polarized blue fluorescence

“…Typical signals from the helicenic fragment were also observed (see ESI†). In common with known helicene-based carbene precursors, 14 the helicene unit is appended onto one N atom of the benzimidazolium core, as opposed to being a fully helical NHC precursor. 10 Note that since imidazolium cation 5 is a charged molecule, its enantiomeric resolution appeared challenging employing the classical chiral HPLC conditions we used, and was thus not considered.…”

Modulation of Chiroptical and Photophysical Properties in Helicenic Rhenium(I) Systems: The Use of an N‐(Aza[6]helicenyl)‐NHC Ligand

“…It is therefore possible to obtain chiral complexes that are attractive as enantioselective catalysts [5,18] or as circularly polarized luminophores, for example. [19][20][21] Using the configurationally stable helical chirality provided by a helicene, an ortho-fused π-conjugated system, [22,23] diverse helically chiral complexes of Au(I), [21,24,25] Au(III), [21] Rh(I), [21] Ru(II), [26] Ni(II), [27] Ir(I), [24] Ir(III), [19,[28][29][30][31] and Cu(I) [32] have been recently prepared and studied. Furthermore, the first chiral NHCÀ Re(I) complexes, A-I and A-Cl, were reported by us in 2020, using an N-(pyridyl)- [5]helicene-imidazolylidene as the : C ^N ligand (A-X in Figure 1).…”

Gold(I)‐N‐Heterocyclic Carbene Synthons in Organometallic Synthesis

“…In 2021, Crassous and co-workers synthesised and studied the luminescent properties of a helically chiral [5]helicene-NHC gold(I) complex bearing an acetylide ligand (61, Figure 5), which is obtained as enantiopure after chiral HPLC. [83] This compound shows both phosphorescence and fluorescence, with high overall quantum yields and high ratio between phosphorescence and fluorescence. Moreover, this gold complex possesses high ECD (Electronic Circular Dichroism) activity, which is strongly correlated with the presence of the helicene ligand, and a clearly detectable CPL (Circularly Polarized Luminescence) activity.…”