[Sc©[3]CPP]+: A Viable Metal-Centered [3]Cycloparaphenylene

[n]Cycloparaphenylenes ([n]CPPs, n denotes the number of phenyl groups) aredifficult tosynthesize because of the strain related to their bent phenyl rings.In particular, the strain in [3]CPP is high enough to destroy the & pi; electron delocalization, leading to the spontaneous structuraltransition to an energetically more stable bond-shift(BS) isomer ([3]BS). In this contribution, we propose to achieve [3]CPPby enhancing the & pi; electron delocalization through hosting aguest metal atom. Our computations revealed that Sc could stabilize[3]CPP by forming the [Sc & COPY;[3]CPP](+) complex throughthe favorable & pi;-Sc donation-backdonation interactions.Thermodynamically, the binding energy between the Sc atom and [3]CPPwas -205.7 kcal/mol, which could well compensate not only theenergy difference of 44.2 kcal/mol between [3]CPP and [3]BS but alsothe extremely high strain energy of 170.3 kcal/mol in [3]CPP. Simultaneously,the [Sc & COPY;[3]CPP](+) complex is stable up to 1500 K indynamic simulations, suggesting its high viability in the synthesis. The extremely high strain in [3]CPP (withdelocalized & pi;electrons) may lead to the spontaneous conversion of the structureto its isomerism with localized & pi; electrons. We propose thatthe desired [3]CPP skeleton can be achieved by restoring the & pi;electron delocalization through the donation and backdonation interactionsbetween the & pi; orbitals of [3]CPP and the valence atomic orbitalsof the scandium atom.

Automated summary

By enhancing the pi electron delocalization through the interaction with a metal atom, a stable compound of Cycloparaphenylenes [3]CPP was achieved, which is of great significance for the synthesis of [3]CPP.