Computational Study of the Effect of Lewis Base Additives and Molecular Spin State in SmI2-Chemistry

Abstract

SmI₂ has become a crucial reagent in organic chemistry due to its ability to facilitate single-electron transfer (SET) reactions under mild conditions, enabling the construction of complex molecular architectures. Its versatility can be further enhanced by the use of additives, particularly Lewis base (LB) additives. In this study, we provide a computational understanding of the multifaceted role of LB additives in SmI₂ chemistry. We first identify the critical interplay between the basicity of the LB and the coordination geometry, which together dictate the reducing power of SmI₂(LB)_n complexes. For example, the relatively weak LB tetrahydrofuran (THF), a less bulky ligand than analogous ethers such as tetrahydropyran (THP), can achieve tight coordination to Sm, thereby enhancing electron donation and the reducing power of SmI₂. Additionally, we investigate the SET reduction of various ketones by SmI₂, showing that both steric and electronic effects from the LB and the substrate play pivotal roles in governing the SET reduction reactivity of SmI₂, suggesting that SET reactivity cannot be solely determined by the commonly used reduction potential of SmI₂. In the final part of our study, we examine the influence of LB additives on practical SmI₂-catalysed coupling reactions, finding a revised reaction mechanism that proceeds along a novel septet pathway that outperforms the conventional quintet route. We find that strongly coordinating additives can markedly reshape the reaction profile by accelerating key steps and altering the rate-determining stationary points. These results highlight how LB additives can intricately modulate reactivity and selectivity, offering valuable insights for the rational design of more efficient and selective SmI₂-mediated transformations.