Unusual Photoreaction of Triquinacene within Self‐Assembled Hosts

Abstract

Triquinacene is a concave tricyclic hydrocarbon with diverse photoreactivity. In the cavity of an electron-accepting molecular host, triquinacene was specifically photooxidized at the peripheral allylic position into an alcohol, 1-hydroxytriquinacene, via guest-to-host electron transfer. The unusual reactivity stems from the extremely electron-deficient triazine panel ligand of the host cage, which allows the cage to function as a good electron acceptor. Thus, self-assembled coordination cages can serve not only as molecular-sized reaction vessels but also function electronically as redox media. Dissolved molecular oxygen is indispensable for the photoreaction and immediately traps a photogenerated radical.

Metal‐Organic Polyhedra: Catalysis and Reactive Intermediates

“…It is worthy of mention that substitution of the triazine ligand with benzene leads to no selective photooxidation and the absence of a cage to formation of polymeric products of the tricyclic hydrocarbon. Moreover, the same photooxidation reaction under the influence of bowl‐shaped cage 2 afforded the alcohol in 60% NMR yield 60. Additionally, the reaction of allylic halides with a nucleophile either at the α or the γ carbon generates two regioisomeric products and the ratio is entirely dependent on the steric, electronic properties and polarity of the solvents.…”

“…M 6 L 4 12+ octahedral cage 1 having an electron‐deficient triazine panel ligand encapsulates the concave tricyclic hydrocarbon triquinacene and photooxidizes it at the peripheral allylic position into 1‐hydroxytriquinacene (35% yield along with 65% of the unreacted cage 1 ) via guest to host electron transfer 60. Mechanistically, the first step is the photoexcitation of the triazine ligand which increases its oxidation ability by inducing electron transfer from the tricyclic hydrocarbon to the triazine ligand resulting in deprotonation from the allylic position and generation of a 1‐triquinacenyl radical stabilized by an adjacent CC bond, the second step is the trapping by O 2 to form a radical and lastly its decomposition to a stable alcohol (Scheme ).…”

Ligand Constraints and Synthesis of Metal–Organic Polyhedra

“…19) prepared by the concept of molecular panelling is employed in a vast number of applications such as [2þ2] homo and cross photodimerisation, [99] Diels-Alder reaction, [100] Knoevenagel condensation, [101] sequence selective recognition of peptides, [102] stabilisation of unstable metal complexes [103] and bimolecular recognition, [104] and photooxidation of concave tricyclic hydrocarbon triquinacene at peripheral allylic position. [105] Recently, the self-aggregation of polyfluorinated compounds in a confined cavity of an octahedral cage has been reported by Fujita and coworkers. A range of polyfluorinated aliphatic compounds aggregated deep inside the cavity with the polar C-H, hydroxyl substituents are sticking out of the portal, whereas no such self-aggregation of polyfluorinated aromatic compounds has been observed due to the absence of p-p stacking interactions with the triazine ligands.…”

Self-assembled metal–organic polyhedra: An overview of various applications

“…Cationic cage 2 encapsulates tricyclic hydrocarbon triquinacene and photo-oxidized it at the peripheral allylic position to form 1-hydroxytriquinacene (35% yield along with 65% of the unreacted cage 2) via guest-to-host electron transfer [132]. Mechanistically, the first step is the photo-excitation of triazine linker to form 1-triquinacenyl radical stabilized by adjacent C=C bond, second step is the trapping of oxygen molecule to form unstable radical and third, its decomposition to stable alcohol ( fig.…”