Hybrids of cationic [4]helicene and N-heterocyclic carbene as ligands for complexes exhibiting (chir)optical properties in the far red spectral window

Abstract

Synthesis, electronic and structural properties of a chiral NHC bearing a N-bonded cationic [4]helicene moiety are reported. This ligand is used to construct Au(I), Au(III) and Rh(I) complexes exhibiting far-red...

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

“…Because of the versatility of NHC chemistry, it is possible to access a great number of molecular structures, including structures containing sources of chirality. It is therefore possible to obtain chiral complexes that are attractive as enantioselective catalysts [5,18] or as circularly polarized luminophores, for example [19–21] . 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), [19,28–31] and Cu(I) [32] have been recently prepared and studied.…”

Chemo‐ and Regioselective Multiple C(sp2)−H Insertions of Malonate Metal Carbenes for Late‐Stage Functionalizations of Azahelicenes

“…[7] Cationic [4], [5] and [6]helicenes, which beneficiate from the extended delocalization provided by the triarylcarbenium framework, are welcome exceptions. [8] DMQA (DiMeth-oxyQuinAcridinium) 7, and related quinacridine derivative 2, are classical representatives of this class of heteroaromatics. [9,10] These moieties are remarkably nucleophilic despite their cationic and heteroaromatic characters.…”

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

“…[a] Measured on the corresponding imidazolium precursor in CDCl 3 ; [b] Measured on the corresponding selenoureas; [c] Measured on the corresponding [NHC−Ir(CO) 2 Cl] complex in CH 2 Cl 2 , TEP was calculated from the average value of the frequencies of the CO bands (in brackets for the first two complexes) following Nolan et al . : TEP (cm −1 )=0.8475 ν average, CO (cm −1 )+336.2 (cm −1 ); [20,21] [d] The two resonances arise from the presence of two atropoisomers [14b] …”

“…It is informative to compare the behavior of 1 and 2 with other Au(I) NHC complexes. Non‐helicenic NHC complexes that do not have extended conjugation in their ligands exhibit only phosphorescence, [28] whilst the recently reported helicenic complex [( rac )‐ 15 ]Au I Cl.PF 6 (Scheme 2) – featuring a highly extended conjugated system – shows only fluorescence in the red region, reminiscent of the N ‐[4]helicenium‐imidazolium ligand [14b] . The dual emission – phosphorescence and fluorescence – of 1 and 2 places them between these two extremes.…”

“…The spectrum of ( P )‐ 2 is identical in terms of the alternation of bands with the exception of the band at 266 nm which appears slightly red‐shifted (about 10 nm) and more intense (Δϵ=−75 M −1 cm −1 ). For comparison, the gold(III) complex [( P )‐ 15 ]Au III L.(PF 6 ) 2 (L=2,6‐diphenylpyridine) recently described [14b] displays ECD bands in acetonitrile in the UV region diagnostic of helicenic derivatives – 237 nm (Δϵ=+23 M −1 cm −1 ), 287 nm (+52), 320 nm (+21) – in addition to observable bands in the red region of somewhat lower intensity —600 nm (Δϵ=+8 M −1 cm −1 ). The lower intensities of [( P )‐ 15 ]Au III L.(PF 6 ) 2 with respect to ( P )‐ 1 can be explained by the smaller length of the helical unit.…”