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The role of halogen bonding (XB) in chemical catalysis has largely involved using XB donors as Lewis acid activators to modulate the reactivity of partner Lewis bases. We explore a more uncommon scenario, where a Lewis base modulates reactivity via a spectator halogen bond interaction. Our computational studies reveal that spectator halogen bonds may play an important role in modulating the rate of SN2 reactions. Most notably, π acceptors such as PF3 significantly decrease the barrier to substitution by decreasing electron density in the very electron rich transition state. Such π-backbonding represents an example of a heretofore unexplored situation in halogen bonding: the combination of both σ-donation and π-backdonation in this "non-covalent" interaction. The broader implications of this observation are discussed. [ABSTRACT FROM AUTHOR]

Electrocatalytic carbon dioxide (CO 2 ) conversion into valuable chemicals paves the way for the realization of carbon recycling. Downsizing catalysts to single-atom catalysts (SACs), dual-atom catalysts (DACs), and sub-nanocluster catalysts (SNCCs) has generated highly active and selective CO 2 transformation into highly reduced products. This is due to the introduction of numerous active sites, highly unsaturated coordination environments, efficient atom utilization, and confinement effect compared to their nanoparticle counterparts. Herein, recent Cu-based SACs are first reviewed and the newly emerged DACs and SNCCs expanding the catalysis of SACs to electrocatalytic CO 2 reduction (CO 2 RR) to high-value products are discussed. Tandem Cu-based SAC-nanocatalysts (NCs) (SAC-NCs) are also discussed for the CO 2 RR to high-value products. Then, the non-Cu-based SACs, DACs, SAC-NCs, and SNCCs and theoretical calculations of various transition-metal catalysts for CO 2 RR to high-value products are summarized. Compared to previous achievements of less-reduced products, this review focuses on the double objective of achieving full CO 2 reduction and increasing the selectivity and formation rate toward C-C coupled products with additional emphasis on the stability of the catalysts. Finally, through combined theoretical and experimental research, future outlooks are offered to further develop the CO 2 RR into high-value products over isolated atoms and sub-nanometal clusters., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)