Are encapsulated nickel cyclams potent for CO₂ activation? Insights from multi-scale modelling

Nickel cyclams are known to activate carbon dioxide (CO₂) and perform the reduction reaction to form carbon monoxide (CO) through the consumption of two protons and two electrons. This catalyst is superior due to its facile operating reduction potential, and it can facilitate CO₂ activation and reduction. Several attempts have been made to enhance the performance of the Ni-cyclam through covalent functionalization. This study focuses on the rational design of a cucurbit-[8]-uril (CB[8]) based Ni-cyclam catalyst for CO₂ activation by utilizing host-guest chemistry. Using multiscale computational techniques, we systematically investigated the potential energy surface of various cyclam derivatives upon encapsulation in the CB[8] cavity and elucidated the encapsulation mechanism. Our simulations demonstrate that Ni-bound derivatives encapsulate more readily than their free-ligand counterparts, suggesting a two-step encapsulation mechanism: initial coordination of the nickel ion to bare cyclam, followed by host uptake of the Ni-cyclam complex into the CB[8] cavity. Electronic structure calculations using the ONIOM method reveal that the T3 diastereomer is thermodynamically favored for Ni-bound cyclam derivatives over other diastereomers. Notably, encapsulation of Ni-cyclam within CB[8] results in a lowered redox potential for the Ni-catalyst, indicating an enhanced catalytic efficiency for CO₂ activation where the CB[8] acts as an electronically innocent host.