Photoelimination of nitrogen from adamantane and pentacycloundecane (PCU) diazirines: a spectroscopic study and supramolecular control

• Published in: Photochemical & photobiological sciences 2019, Vol.18 (7), p.186-1822
• Main Authors: Šumanovac, Tatjana, Aleškovi, Marija, Šekutor, Marina, Matkovi, Marija, Baron, Thibaut, Mlinari -Majerski, Kata, Bohne, Cornelia, Basari, Nikola
• Format: Article
• Language: English
• Subjects: Atmospheric chemistry; Biochemistry; Biomaterials; Carbenes; Chemistry; Circular dichroism; Computer applications; Cyclodextrin; Cyclodextrins; Dichroism; Flash photolysis; Fluorescence; Inclusion complexes; Investigations; Irradiation; Ketones; Magnetic resonance spectroscopy; Nitrogen; NMR; NMR spectroscopy; Nuclear magnetic resonance; Organic chemistry; Photochemicals; Photolysis; Physical Chemistry; Plant Sciences; Protonation; Quantum chemistry; Reactivity; Solvents; Spectroscopy
• ISSN: 1474-905X; 1474-9092
• DOI: 10.1039/c9pp00124g

Photochemical reactivity of pentacycloundecane (PCU) and adamantane diazirines was investigated by preparative irradiation in different solvents, laser flash photolysis (LFP) and quantum chemical computations. In addition, formation of inclusion complexes for diazirines with cucurbit[7]uril, β- and γ-cyclodextrin (β- and γ-CD) was investigated by 1 H NMR spectroscopy, isothermal microcalorimetry and circular dichroism spectroscopy, followed by the investigation of photochemical reactivity of the formed complexes. Diazirines undergo efficient photochemical elimination of nitrogen ( Φ R > 0.5) and deliver the corresponding singlet carbenes. Singlet carbenes react in intra- and intermolecular reactions and we found a rare singlet carbene pathway in CH 3 OH involving protonation and formation of a carbocation, detected due to the specific rearrangement of the pentacycloundecane skeleton. Singlet diazirines undergo intersystem crossing and deliver triplet carbenes that react with oxygen to form ketones which were isolated after irradiation. Our main finding is that the formation of diazirine inclusion complexes with β-CD and γ-CD changes the relative ratio of singlet vs. triplet pathways, with singlet carbene products being dominant from the chemistry of the irradiated complexes. Our combined theoretical and experimental studies provide new insights into the supramolecular control of carbene reactivity which has possible applications for the control of product distribution by solvent effects and the choice of constrained media. Nitrogen photoelimination delivers carbenes from diazirines. Protonation of singlet carbenes was detected based on the PCU skeleton rearrangement. Complexation of diazirines changes the relative singlet/triplet ratio of carbene products.