Helquats: A Facile, Modular, Scalable Route to Novel Helical Dications

Three tricyclic diquats with an eight-membered ring were prepared and shown to be the first configurationally stable derivatives of their kind. Resolution was achieved by using chiral hexacoordinated phosphorus BINPHAT and TRISPHAT anions. The diquat cations were obtained in high diastereo- and enantiomeric purity (ee>96% in most cases). X-ray diffraction analysis coupled with circular dichroism (CD) measurements allowed a precise determination of the relative and absolute configuration of the salts. The barriers to racemization of these compounds were calculated by using CD time-course measurements at different temperatures, affording DeltaG(++) values above 25 kcal mol(-1). Derivatives 4a, 4b, and 4c are the first eight-membered-ring derivatives with only three ring constraints to be resolved. This manuscript also reports the first procedure to remove TRISPHAT anions after diastereomeric separation.

Section: Resultsmentioning

confidence: 99%

Resolution of the First Nonracemic Diquats

Vachon

Bérnardinelli

Lacour

2010

“…Furthermore, few other examples of electroactive helicene derivatives have been described in the literature 22. For example, helicene and azahelicenes undergo multi‐reduction processes,22a,b and paraquinone‐22c or thiophene‐incorporating22d helicenes can be, respectively, reduced or oxidized into the corresponding radical anion or cation. Other examples are given by mono‐ and bis‐cobaltocenium‐fused [7]helicenes,22e and recent ferrocenyl‐alkynyl‐tetrathia[7]helicenes 22f…”

Section: Resultsmentioning

confidence: 99%

Ruthenium‐Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching

Srebro

Anger

Moore

et al. 2015

The properties of mono- and bis-Ru-vinyl[6]helicene complexes (2 a and 2 b, respectively), recently synthesized by using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π-helical backbone through a vinyl bridge, are presented. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV/Vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in the neutral and oxidized states ([2 a](·+), [2 b](·+), and [2 b](2+)), are analyzed with the aid of quantum-chemical calculations. The extended π-conjugation facilitated by the vinyl moiety, clearly visible in the electronic structures of 2 a,b, introduces new active bands in the ECD spectra that consequently lead to a significant increase in optical rotation of Ru-vinylhelicenes compared with the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both the organic and organometallic species and constitute the first examples of VCD for metal-based helicene derivatives. Finally, the redox-triggered chiroptical switching activity of 2 a,b is examined in detail by using ECD spectroscopy. The modifications of the ECD spectra in the UV/Vis and NIR region are well reproduced and rationalized by calculations.

“…Although a number of emissive helical cationic‐type molecules have been reported,8, 10, 21 their Φ PL values were not usually determined, which makes comparisons difficult. However, Clennan and co‐workers recently reported a dicationic helicene, which contained two N ‐methylated quartenary ammonium centres that emitted with Φ PL of 6.6 % 10.…”

Section: Methodsmentioning

confidence: 99%

One‐Pot Synthesis of Highly Emissive Dipyridinium Dihydrohelicenes

Santoro

Lord

Loughrey

et al. 2015

yesCondensation of a pyridyl-2-carbaldehyde derivative\ud with 2-(bromoethyl)amine hydrobromide gave tetracyclic\ud pyrido[1,2-a]pyrido[1’,2’:3,4]imidazo-[2,1-c]-6,7-dihydropyrazinium\ud dications in excellent yields. Crystal structures\ud and NOE data demonstrated the helical character of\ud the dications, the dihedral angles between the two pyrido\ud groups ranging from 28–458. An intermediate in the synthesis\ud was also characterized. A much brighter emission\ud compared to literature helicenes has been found, with\ud quantum yields as high as 60% in the range of l=460–\ud 600 nm. Preliminary cytotoxicity studies against HT-29\ud cancer cells demonstrated moderate-to-good activity, with\ud IC50 values 12–30x that of cisplatin.emailed RM Lord for final draft 28.09.2016 - sm\ud \ud © YYYY Wiley\ud This is the peer reviewed version of the following article: [FULL CITE], which has been published in final form at [Link to final article using the DOI]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving