Stereospecific Winding of Polycyclic Aromatic Hydrocarbons into Trinacria Propellers

• Published in: Chemistry : a European journal Vol. 23; no. 61; pp. 15348 - 15354
• Main Authors: Mosca, Dario, Stopin, Antoine, Wouters, Johan, Demitri, Nicola, Bonifazi, Davide
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 02.11.2017; Wiley Subscription Services, Inc
• Subjects: aromatic embrace; Benzene; Chemistry; Chemistry, Multidisciplinary; chirality; Conformation; Denaturation; High temperature; molecular motors; molecular propellers; Physical Sciences; polycycles; Polycyclic aromatic hydrocarbons; Propellers; Proton resonance; Science & Technology; X-ray diffraction; CHIRAL RECOGNITION; chirality; PHENYL EMBRACES; aromatic embrace; molecular motors; ARTIFICIAL MOLECULAR MACHINES; PROTOTYPES; CONFIGURATIONAL STABILITY; molecular propellers; SWITCHES; CRYSTAL SUPRAMOLECULARITY; MOTORS; METAL-COMPLEXED CATENANES; ROTAXANES; polycycles
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201702032

The stereospecific trimerization of enantiomerically pure binaphthols with hexakis(bromomethyl)benzene gives access in one step to enantiomerically pure molecular propellers, in which three binaphthyl rings are held together with dioxecine rings. X‐ray diffraction analysis revealed that three out the six naphthyl moieties are folded in a (EF)3‐type arrangement held by three intramolecular C−H⋅⋅⋅π interactions. This slips outward the three remaining naphthyl rings in a blade‐like fashion, just like in three‐folded propeller components. This peculiar conformation shows striking similarity to the mythological Sicilian symbol of Trinacria, from which the name “trinacria propeller” derives. The propeller conformation is also preserved in chlorinated solutions, as displayed by the presence of a peak at 4.7 ppm typical of an aromatic proton resonance engaged in a C−H⋅⋅⋅π interaction. The denaturation of the propeller‐like conformation is obtained at high temperature, corresponding to activation energy for the ring inversion of ca. 18.2 kcal mol−1. Notably, halide‐functionalized molecular propellers exposing I‐atoms at the leading and trailing edges could be prepared stereo‐ and regiospecifically by choosing the relevant iodo‐bearing BINOL derivative. Carbon nanostructures: The stereospecific trimerization of enantiomerically pure binaphthols with hexakis(bromomethyl)benzene gives access in one step to enantiomerically pure propellers. Three out the six naphthyl moieties are folded in an embraced conformation held by three intramolecular C−H⋅⋅⋅π interactions. This slips outward the three remaining naphthyl rings in a blade‐like fashion, just like in three‐folded propeller components. This peculiar conformation shows striking similarity to the mythological Sicilian symbol of Trinacria, from which the name “trinacria propeller” derives.