Unique Bora[1]ferrocenophanes with Sterically Protected Boron: A Potential Gateway to Helical Polyferrocenes. (16th October 2019)

• Record Type: Journal Article
• Authors: Bhattacharjee, Hridaynath; Zhu, Jianfeng; Müller, Jens
• Is Part Of: Angewandte Chemie. Volume 131:Number 46(2019)
• Page Start: 16728
• Page End: 16735
• Publication Date: 2019-10-16
• Subjects: Boron -- Chiralität -- Gespannte Moleküle -- Helikale Strukturen -- Ringöffnende Polymerisation; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.201908993
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: Silicon‐bridged [1]ferrocenophanes are a versatile class of monomers to obtain well‐defined metallopolymers, however, their boron‐bridged analogues are far less utilized despite being significantly higher strained. We assumed that the reactivity of known bora[1]ferrocenophanes towards ring‐opening polymerization is hampered by π‐donating R2 N groups at the bridging boron atom and therefore prepared the first bora[1]ferrocenophanes lacking such electronic stabilization. The new, isolated ferrocenophane with a 2, 4, 6‐triisopropylphenyl group attached to the bridging boron atom exhibits the most tilted Cp rings among all isolated strained sandwich compounds [α(DFT)=33.3°] with a measured record value of the bathochromic shift ( λ max =516 nm). Attempts to purify the mesityl analogue by vacuum sublimation transformed this monomer to a purple‐colored polymer that resulted in Cotton effects in circular dichroism spectroscopy. DFT calculations revealed a left‐handed helical structure for this polymer. This is the first evidence for a polyferrocene with a chiral secondary structure. Abstract : Verkippter Drehwurm : Eine neue Klasse chiraler [1]Ferrocenophane mit der bislang stärksten bekannten Verkippung der Cp‐Ringe wird vorgestellt. Aus einem der Monomere wurde ein Poly(ferrocenylboran) erhalten, das DFT‐Rechnungen zufolge eine linkshändige helikale Struktur aufweist. Dies sind erste Belege für ein Polyferrocen mit chiraler Sekundärstruktur.