Organic/Inorganic/Materials Chemistry Seminars
Boekelheide Lecture Series
Professor Graham Bodwell, Memorial University of Newfoundland
Hosted by Mike Haley
May 29, 2024 · 2:00 pm, 115 Lawrence Hall
Synthesis, Properties and Chemistry of Cyclophanes Containing Nonplanar Polycyclic Aromatic Hydrocarbons
Nonplanar aromatic compounds are interesting molecules because they provide opportunities to learn how chemical and physical properties are affected by changes in structure. Such compounds are challenging synthetic targets due to fact that they are strained, and the level of synthetic challenge typically increases with the amount of strain. As a result, powerful synthetic methodology and effective general strategies are required to enable the synthesis of such compounds, especially those that are at more highly strained. Details of our work aimed at the synthesis and study of cyclophanes that contain bent aromatic systems will be presented.
May 31, 2024 • 3:00 pm, 110 WIL Hall
[n](2,11) Teropyrenophanes: Models for Probing Armchair Edge Chemistry in Nanocarbons and a Platform for the Design of Mixed Cyclophanes with Unusual Properties
Teropyrene, a C36 PAH, is the largest PAH to have been systematically bent out of planarity through its incorporation into a series of [n]cyclophanes (those that consist of a single aromatic system and a single aliphatic bridge).[1] In this series of cyclophanes (1, n = 7-10), the end-to-end bend in the teropyrene ranges from q = 145° to 178°. The teropyrene system undergoes highly regioselective electrophilic aromatic substitution (bromination) and this can be understood in terms of a combination of steric and electronic effects. Furthermore, the chemical reactivity of the teropyrene system toward bromination increases substantially as it becomes more bent.[2] The K-regions can also be oxidized to afford diones that have been π-extended to afford a series of [n]heterocyclophanes. APEX chemistry has also been achieved with high regioselectivity in the synthesis of a cyclophane with C84 aromatic system.
More recently, a large, strained (SE = 44.2 kcal/mol) and conformationally flexible mixed [3.3]cyclophane of pyridine and teropyrene (2) was synthesized using two intramolecular Wurtz coupling reactions and an unprecedented Scholl reaction between the unreactive 2 positions of the pyrene systems in a triply-bridged pyrenophane.[3] Protonation of the pyridine unit results in a greatly enhanced preference for nesting in the cavity of the highly bent teropyrene system (qcalc = 162.6°) and emergence of a charge transfer absorption band (lmax = 592 nm) due to a long range (5.0-5.5 Å), through-space intramolecular transition between the teropyrene and pyridinium units, which does not exist in the neutral cyclophane
References
1. Unikela, K. S.; Ghods Ghasemabadi, P.; Houska, V.; Dawe, L. N.; Zhao, Y.; Bodwell, G. J. “Chem. – Eur. J. 2021, 27, 390–400
2. Unikela, K. S.; Roemmele, T. L.; Houska, V.; McGrath, K. E.; Tobin, D. M.; Dawe, L. N.; Boeré, R. T.; Bodwell, G. J. Angew. Chem. Int. Ed. 2018, 57, 1707–1711.
3. Ghods Ghasemabadi, P.; Tabasi, Z. A.; Salari, P.; Zhao, Y.; Bodwell, G. J. Chem. – Eur. J. 2023, 29, e202302404