Helicene-based transition metal complexes: synthesis, properties and applications

Saleh, Nidal; Shen, Chengshuo; Crassous, Jeanne

doi:10.1039/c4sc01404a

Cited by 220 publications

(166 citation statements)

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“…However, one of the first results on the use of helicenes as chiral auxiliaries in few diastereoselective reactions was reported in 1985-1987 by Martin et al with racemic 2-substituted- [7]helicene [46][47][48][49][50]. Hence, racemic 29 was employed as an inbuilt chiral auxiliary for the diastereoselective reaction of the carbonyl group of α-keto esters upon reduction with NaBH 4 , yielding 30 (99% yield; 100% de) [46], and on the nucleophilic addition of Grignard reagent to give 31 (95% yield; 100% de) [47] (Scheme 1).…”

Section: Helicenes As Chiral Auxiliary/reagent or Additivementioning

confidence: 99%

“…The mechanism includes the initial reaction between enantiopure 2-cyano- [7]helicene 37 and H2O2 to generate in situ the corresponding chiral hydroperoxyimine, which serves as a chiral oxidizing reagent for the subsequent epoxidation of alkenes 35 and 39, whilst itself converting finally to [7]helicene-2-carboxamide 42.…”

Section: Helicenes As Chiral Auxiliary/reagent or Additivementioning

confidence: 99%

“…Similarly, [7]helicene-attached unsaturated ester 32 was also utilized for the highly diastereoselective ene reaction with cyclohexene 33 in the presence of SnCl 4 to afford 34 with high yield (86%) and 100% de [48] (Scheme 2). up.…”

Section: Helicenes As Chiral Auxiliary/reagent or Additivementioning

confidence: 99%

“…In the latter, whilst the overall molecule is heterocyclic, the helicene core is not. Further, depending on the heteroatom nature, the helicene structures are named aza [5]helicenes (13 [23], 14 [24]), oxa [5]helicenes (15 [25]), and thia [7]helicenes (16 [26]). If there is more than one heteroaromatic ring or heteroatom, the helicene names are simplified as hetero [n]helicenes, [n]heterohelicenes, or simply [n]helicenes.…”

Section: Heterohelicenesmentioning

confidence: 99%

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Helicene-Based Chiral Auxiliaries and Chirogenesis

Hasan

Borovkov

2017

Symmetry

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Helicenes are unique helical chromophores possessing advanced and well-controlled spectral and chemical properties owing to their diverse functionalization and defined structures. Specific modification of these molecules by introducing aromatic rings of differing nature and different functional groups results in special chiroptical properties, making them effective chiral auxiliaries and supramolecular chirogenic hosts. This review aims to highlight these distinct structural features of helicenes; the different synthetic and supramolecular approaches responsible for their efficient chirality control; and their employment in the chirogenic systems, which are still not fully explored. It further covers the limitation, scope, and future prospects of helicene chromophores in chiral chemistry.

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Section: Helicenes As Chiral Auxiliary/reagent or Additivementioning

confidence: 99%

Section: Helicenes As Chiral Auxiliary/reagent or Additivementioning

confidence: 99%

Section: Helicenes As Chiral Auxiliary/reagent or Additivementioning

confidence: 99%

Section: Heterohelicenesmentioning

confidence: 99%

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Helicene-Based Chiral Auxiliaries and Chirogenesis

Hasan

Borovkov

2017

Symmetry

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“…On the other hand, a 2,2 -bipyridine (bpy) ligand has been functionalized with a [6]-helicene to enhance the luminescence. Indeed, the latter presents a π-conjugated backbone of aromatic rings, configurationally stable for n ≥ 5, and its peculiar topology results in intense emission [31,32]. Moreover, [n]-helicene ligands are helically-shaped, so they possess a chirality despite the absence of enantiocenter.…”

Section: Introductionmentioning

confidence: 99%

Slow Magnetic Relaxation in Chiral Helicene-Based Coordination Complex of Dysprosium

et al. 2016

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Abstract:The complex [Dy(L)(tta) 3 ] with L the chiral 3-(2-pyridyl)-4-aza[6]-helicene ligand (tta − = 2-thenoyltrifluoroaacetonate) has been synthesized in its racemic form and structurally and magnetically characterized. [Dy(L)(tta) 3 ] behaves as a single molecule magnet in its crystalline phase with the opening of a hysteresis loop at 0.50 K. These magnetic properties were interpreted with ab initio calculations.

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Structure and Property Diversity of Chiral Helicene Oligomers

Saito

Shigeno

Yamaguchi

2015

Encyclopedia of Polymer Science and Technology

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alkylthio, and perfluoroalkyl groups. In addition, cyclization of helicene oligomers provides another method of obtaining diversity.A notable aspect in the diversity of helicene oligomers is that they can be connected to provide multidomain oligomers (Fig. 4). When two helicene oligomers are connected, they are referred to herein as homo-bidomain oligomers. Cyclic homo-bidomain oligomers are also conceivable. Hetero-multidomain oligomers can be obtained by connecting different structures of oligomers. Such manipulations provide a large diversity of structures.Because helicene can generate characteristic π−π interactions, helicene oligomers often form bimolecular, trimolecular, tetramolecular, and polymolecular aggregates in which homoaggregation and heteroaggregation can also occur. Such aggregates self-assemble to form fibrils, vesicles, liquid crystals, and surface monolayers. These noncovalent bonding interactions provide diversity of the structure of helicene oligmers. Diverse Properties of Helicene OligomersStructural diversity is directly related to diversity of properties, and the properties of a helicene oligomer can be varied by structural modifications. In addition, multidomain oligomers can be designed, in which properties A and B of each domain can be combined. Such compounds exhibit property A + B or even another property C, a result regarded as the "synthesis of a property or function." Aggregation and self-assembly of helicene oligomers further increase property diversity, which covers materials with a broad range of sizes from subnanometersized molecules through nano-and micrometer-sized molecular aggregates and molecular self-assemblies to macroscopic bulk materials. Helicene oligomers are sensitive to changes in the environment such as temperature, solvent, and concentration. Different properties appear in dilute solution, in concentrated Amidohelicene oligomers: (a) acylcic oligomers (P)-1 (n = 1−9) with dianiline spacer, cyclic oligomers (P)-2 (n = 1−10) with dianiline spacer, (b) acyclic oligomers (P)-3 (n = 1−9) with m-phenylene spacer, and acyclic reverse oligomers (P)-4 (n = 1−4). (c) Schematic representation of reversible change between helix dimer and random coils of (P)-3 and (P)-4. solution, in the crystalline state, in the amorphous state, on the solid surface, at the solid-liquid interface, in fiber assemblies, in liquid crystals, and in gels. Dynamic properties of helicene oligomers are also interesting, and structural changes are largely affected by the environment, providing a stimulus response or possible molecular switching materials. It is also noteworthy that the process of a structure change can produce unusual transient phenomena. Amidohelicene OligomersStudies on helicene oligomers were initiated with amide derivatives (Fig. 5a, top), in which the spacer has a bent shape and includes both hydrogen bonding donor and acceptor moieties (24). (P)-5,8-Helicenedicarboxylate was reacted with bis(2,6-dimethylanilino)cyclohexane to give a series of acyclic helicene oligomers 1 up t...

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Helicene-based transition metal complexes: synthesis, properties and applications

Cited by 220 publications

References 89 publications

Helicene-Based Chiral Auxiliaries and Chirogenesis

Helicene-Based Chiral Auxiliaries and Chirogenesis

Slow Magnetic Relaxation in Chiral Helicene-Based Coordination Complex of Dysprosium

Structure and Property Diversity of Chiral Helicene Oligomers

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