Synergy of liberated anions and intense electric field in frustrated ion pairs for enhancing CO ₂ cycloaddition

Frustrated Lewis pairs (FLPs) have emerged as a transformative strategy in small-molecule activation, leveraging steric inhibition to sustain highly reactive Lewis acid-base pairs capable of heterolyzing nonpolar molecules such as H₂ and CO₂ through electric field (EF)-induced polarization. Despite their promise, FLPs exhibit inherent limitations in activating highly stable, kinetically inert substrates, owing to insufficient field strength and limited polarization efficacy. The systems with intensified charge separation, termed frustrated ion pairs (FIPs), can transcend these constraints by combining extreme ionic reactivity with persistent frustration. Here, we propose a geometrically controlled FIPs system that systematically modulates interionic distance and interaction via cation size engineering, ensuring sustained frustration and remarkable catalytic enhancement. The relationship between the interaction strength of anions and cations in the FIPs and their performance in CO₂ cycloaddition exhibits a volcanic curve trend. FIPs catalysts with optimal distance (4.11 Å) and interaction strength (-78 kJ·mol^-1·Å^-1) between its cation and anion exhibit optimal catalytic performance (<i>TOF</i> = 184 hour^-1). The frustrated configuration liberates Br^- from electrostatic confinement, achieving unprecedented nucleophilic activity by reducing the ring-opening energy barrier by 48.7 kJ·mol^-1 compared to conventional ionic pairs. Optimal ion-pair distance in FIPs generates an intense asymmetric electric field that strongly polarizes CO₂, yielding an induced dipole moment of ∆μ = 0.132 D. Moreover, the FIPs structure is extended to heterogeneous systems and exhibits a similar trend with homogeneous ones, showing its application potential.