Chirality Relay in 2,2′-Substituted 1,1′-Binaphthyl: Access to Propeller Chirality of the Tricoordinate Boron Center

• Published in: Chemistry : a European journal Vol. 22; no. 47; pp. 16750 - 16754
• Main Authors: Wang, Chen, Sun, Zuo-Bang, Xu, Qing-Wen, Zhao, Cui-Hua
• Format: Journal Article
• Language: English
• Published: WEINHEIM Blackwell Publishing Ltd 14.11.2016; Wiley; Wiley Subscription Services, Inc
• Subjects: 1,1′-binaphthyl; 1′-binaphthyl; Boron; Chemistry; Chemistry, Multidisciplinary; Chirality; chirality relay; Crystals; Mathematical analysis; Physical Sciences; propeller chirality; Propellers; Relay; Rings (mathematics); Science & Technology; Strategy; triarylborane; π-stacking; CIRCULARLY-POLARIZED LUMINESCENCE; POLYMERS; TRIMESITYLMETHANE; IONS; chirality relay; triarylborane; pi-stacking; propeller chirality; ORGANOBORON-BASED BIPHENYLS; PI-ELECTRON SYSTEMS; DYNAMIC STEREOCHEMISTRY; CONFORMATIONAL-ANALYSIS; EMISSION; 1,1 '-binaphthyl; TRIARYLBORANES; π-stacking; 1,1′-binaphthyl
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201602984

It is a challenging issue to achieve propeller chirality for triarylboranes owing to the low transition barrier between the P and M forms of the boron center. Herein, we report a new strategy to achieve propeller chirality of triarylboranes. It was found that the chirality relay from axially chiral 1,1′‐binaphthyl to propeller chirality of the trivalent boron center can be realized when a Me2N and a Mes2B group (Mes=mesityl) are introduced at the 2,2′‐positions of the 1,1′‐binaphthyl skeleton (BN‐BNaph) owing to the strong π–π interaction between the Me2N‐bonded naphthyl ring and the phenyl ring of one adjacent Mes group, which not only exerts great steric hindrance on the rotation of the two Mes groups but also gives unequal stability to the two configurations of the boron center for a given configuration of the binaphthyl moiety. The stereostructures of the boron center were fully characterized through 1H NMR spectroscopy, X‐ray crystal analyses, and theoretical calculations. Detailed comparisons with the analog BN‐Ph‐BNaph, in which the Mes2B group is separated from 1,1′‐binaphthyl by a para‐phenylene spacer, confirmed the essential role of π–π interaction for the successful chirality relay in BN‐BNaph. Chirality relay from axially chiral 1,1′‐binaphthyl to propeller chirality of the trivalent boron center can be realized when a Me2N and a Mes2B group (Mes=mesityl) are introduced at the 2,2′‐positions of the 1,1′‐binaphthyl skeleton, providing an efficient strategy to achieve propeller chirality of triarylboranes. Strong intramolecular π–π interactions play an essential role for the successful chirality relay.