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The first enantiopure chiral‐at‐rhenium complexes of the form fac‐ReX(CO)3(:C^N) have been prepared, where :C^N is a helicene‐N‐heterocyclic carbene (NHC) ligand and X=Cl or I. These have complexes show strong changes in the emission characteristics, notably strongly enhanced phosphorescence lifetimes (reaching 0.7 ms) and increased circularly polarized emission (CPL) activity, as compared to their parent chiral models lacking the helicene unit. The halogen along with its position within the dissymmetric stereochemical environment strongly affect the photophysics of the complexes, particularly the phosphorescence quantum yield and lifetime. These results give fresh insight into fine tuning of photophysical and chiroptical properties of Re‐NHC systems. [ABSTRACT FROM AUTHOR]

Novel [4, 6]helicenes (4a,b) bearing a fused imidazolium unit have been prepared from [4, 6]helicene‐2,3‐di‐n‐propyl‐amines 3a,b. The in situ formation of N‐heterocyclic carbene (NHC) derivatives followed by their complexation to iridium(I) or rhodium(I) gave access to complexes 1a, 1′a, and 1b, containing mono‐coordinated helicene‐NHC, chloro and COD (COD = 1,5‐cyclooctadiene) ligands. Ir and Rh complexes 1a and 1′a were characterized by X‐ray crystallography. HPLC and NMR analyses showed that Ir(I) complex 1b existed as a mixture of two diastereomeric complexes corresponding to enantiomeric pairs M‐(−)/P‐(+)‐1b1 and M‐(−)/P‐(+)‐1b2 which differ by the position of COD through space. The chiroptical properties (electronic circular dichroism and optical rotation) of the four stereoisomers were measured. These complexes were also tested as catalysts in a transfer hydrogenation reaction. [ABSTRACT FROM AUTHOR]

A fused π-helical N-heterocyclic carbene (NHC) system was prepared and examined through its diastereoisomerically pure cycloiridiated complexes. The latter display light-green phosphorescence with unusually long lifetimes and circular polarization that depends on both the helical NHC P/ M stereochemistry and the iridium Δ/Λ stereochemistry. These unprecedented features are attributed to extended π conjugation within the helical carbenic ligand and efficient helicene-NHC-Ir interaction. [ABSTRACT FROM AUTHOR]

Innentitelbild: Long-Lived Circularly Polarized Phosphorescence in Helicene-NHC Rhenium(I) Complexes: The Influence of Helicene, Halogen, and Stereochemistry on Emission Properties (Angew. Keywords: circularly polarized emission; helicenes; N-heterocyclic carbenes; phosphorescence; rhenium(I) EN circularly polarized emission helicenes N-heterocyclic carbenes phosphorescence rhenium(I) 8382 8382 1 05/18/20 20200525 NES 200525 B Zeitaufgelöste impulsive b stimulierte Raman-Spektroskopie, eine ultraschnelle Raman-Technik, ermöglicht es, Momentaufnahmen von Molekülen im angeregten Zustand mit hoher Empfindlichkeit und Zeitauflösung zu gewinnen. Circularly polarized emission, helicenes, N-heterocyclic carbenes, phosphorescence, rhenium(I). [Extracted from the article]