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

Abstract

[n]­Cycloparaphenylenes ([n]­CPPs, n denotes the number of phenyl groups) are difficult to synthesize because of the strain related to their bent phenyl rings. In particular, the strain in [3]­CPP is high enough to destroy the π electron delocalization, leading to the spontaneous structural transition to an energetically more stable “bond-shift” (BS) isomer ([3]­BS). In this contribution, we propose to achieve [3]­CPP by enhancing the π electron delocalization through hosting a guest metal atom. Our computations revealed that Sc could stabilize [3]­CPP by forming the [Sc©[3]­CPP]+ complex through the favorable π-Sc donation–backdonation interactions. Thermodynamically, the binding energy between the Sc atom and [3]­CPP was −205.7 kcal/mol, which could well compensate not only the energy difference of 44.2 kcal/mol between [3]­CPP and [3]­BS but also the extremely high strain energy of 170.3 kcal/mol in [3]­CPP. Simultaneously, the [Sc©[3]­CPP]+ complex is stable up to 1500 K in dynamic simulations, suggesting its high viability in the synthesis.