Unique Bora[1]ferrocenophanes with Sterically Protected Boron: A Potential Gateway to Helical Polyferrocenes. Issue 46 (16th October 2019)

• Record Type: Journal Article
• Authors: Bhattacharjee, Hridaynath; Zhu, Jianfeng; Müller, Jens
• Is Part Of: Angewandte Chemie international edition. Volume 58:Issue 46(2019)
• Page Start: 16575
• Page End: 16582
• Publication Date: 2019-10-16
• Subjects: boron -- chirality -- helical structures -- ring-opening polymerization -- strained molecule; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201908993
• Languages: English
• ISSNs: 1433-7851

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 : Tilt a whirl : A new class of chiral [1]ferrocenophanes is described that feature a record‐high Cp ring tilt. From one of the monomers a poly(ferrocenylborane) was obtained that, according to DFT calculations, exhibits a left‐handed helical structure. This is the first evidence of a polyferrocene with a chiral secondary structure.