Long-lived localised singlet diradicaloids with carbon-carbon π-single bonding (C-π-C)

Area of Science:

• Organic Chemistry
• Physical Chemistry
• Chemical Bonding

Background:

• Singlet cyclopentane-1,3-diyl diradicaloids are key intermediates for carbon-carbon π-single bonds (C-π-C).
• High reactivity of these diradicaloids hinders detailed investigation of their chemical properties.

Purpose of the Study:

• To summarize recent advancements in the kinetic stabilization of singlet cyclopentane-1,3-diyl diradicaloids.
• To explore the influence of macrocyclic systems, specifically the "stretch effect" and "solvent dynamic effect", on diradicaloid stability.

Main Methods:

• Investigated kinetic stabilization of singlet diradicaloids using macrocyclic systems.
• Compared lifetimes of macrocyclic diradicaloids (S-DR4a/b, S-DR4d) with a non-macrocyclic parent (S-DR2).
• Examined the impact of viscous solvents on diradicaloid lifetimes.

Main Results:

• Macrocyclic singlet diradicaloids (S-DR4a/b, S-DR4d) exhibited significantly longer lifetimes (up to 156 μs) compared to the parent (S-DR2, 209 ns) at 293 K.
• The dynamic solvent effect was observed for the first time in intramolecular σ-bond formation, extending S-DR4d lifetime to 400 μs in glycerin triacetin.
• Experimental data validated the "stretch effect" and "solvent dynamic effect" for kinetic stabilization.

Conclusions:

• Macrocyclic systems effectively stabilize singlet cyclopentane-1,3-diyl diradicaloids via "stretch" and "solvent dynamic" effects.
• This stabilization strategy allows for the isolation of carbon-carbon π-single bonded species (C-π-C).
• The findings contribute to a deeper understanding of chemical bonding and diradicaloid chemistry.