An official website of the United States government
Abstract The first enantiopure chiral‐at‐rhenium complexes of the formfac‐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.
more »
« less
Helical Chiral N‐Heterocyclic Carbene Ligands in Enantioselective Gold Catalysis
Abstract The first chiral helicene‐NHC gold(I) complexes efficient in enantioselective catalysis were prepared. The L‐shaped chiral ligand is composed of an imidazo[1,5‐a]pyridin‐3‐ylidene (IPy) scaffold laterally substituted by a configurationally stable [5]‐helicenoid unit. The chiral information was introduced in a key post‐functionalization step of a NHC‐gold(I) complex bearing a symmetrical anionic fluoreno[5]helicene substituent, leading to a racemic mixture of complexes featuring three correlated elements of chirality, namely central, axial and helical chirality. After HPLC enantiomeric resolution, X‐ray crystallography and theoretical calculations enabled structural and stereochemical characterization of these configurationally stable NHC‐gold(I) complexes. The high potential in asymmetric catalysis is demonstrated in the benchmark cycloisomerization of N‐tethered 1,6‐enynes with up to 95 : 5 er.
more »
« less
- Award ID(s):
- 1855470
- PAR ID:
- 10446099
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 28
- Issue:
- 17
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The photophysical and chiroptical properties of a novel, chiral helicene‐NHC−Re(I) complex bearing anN‐(aza[6]helicenyl)‐benzimidazolylidene ligand are described, showing its ability to emit yellow circularly polarized luminescence. A comparative analysis of this new system with other helicene‐Re(I) complexes reported to date illustrates the impact of structural modifications on the emissive and absorptive properties.more » « less
-
Abstract Cyclopentene rings possessing a chiral quaternary center are important structural motifs found in various natural products. In this work, we disclose expedient and efficient access to this class of synthetically valuable structuresviahighly enantioselective desymmetrization of prochiral propargylic alcohols. The efficient chirality induction in this asymmetric gold catalysis is achievedviatwo‐point bindings between a gold catalyst featuring a bifunctional phosphine ligand and the substrate homopropargylic alcohol moiety—an H‐bonding interaction between the substrate HO group and a ligand phosphine oxide moiety and the gold‐alkyne complexation. The propargylic alcohol substrates can be prepared readilyviapropargylation of enoate and ketone precursors. In addition to monocyclic cyclopentenes, spirocyclic and bicyclic ones are formed with additional neighboring chiral centers of flexible stereochemistry in addition to the quaternary center. This work represents rare gold‐catalyzed highly enantioselective cycloisomerization of 1,5‐enynes. Density functional theory (DFT) calculations support the chirality induction model and suggest that the rate acceleration enabled by the bifunctional ligand can be attributed to a facilitated protodeauration step at the end of the catalysis.more » « less
-
Abstract Enantioselective, intermolecular alkene arylamination was achieved through gold redox catalysis. Screening of ligands revealed chiral P,N ligands as the optimal choice, giving alkene aminoarylation with good yields (up to 80 %) and excellent stereoselectivity (up to 99 : 1er). As the first example of enantioselective gold redox catalysis, this work confirmed the feasibility of applying a chiral ligand at the gold(I) stage, with the stereodetermining step (SDS) at the gold(III) intermediate, thus opening up a new way to conduct gold redox catalysis with stereochemistry control.more » « less
-
A method is provided for using twisted acenes, and more particularly to configurationally stable twisted acenes that are imbedded into the structure of [7]helicene at the fulcrum ring to form useable material structures. The helicene propa- gates its chiral nature into the acene, while acting as a locking mechanism to thermal racemization. These doubly- helical compounds are part of a new homologous series of polycyclic aromatic hydrocarbons, namely the [7]helitwis- tacenes. Such [7]helitwistacenes have utility as materials suitable for forming a circularly polarized organic light emitting diode (CP-OLED) for direct emission of circularly polarized (CP) light for the fabrication of high efficiency electronic displays.more » « less
