Mechanistic Diversity of Mg(I)-Mediated 2-6-CO Coupling Revealed through Computational Reaction Path Exploration

Reductive coupling of CO in homogeneous systems has long been used to model the Fischer-Tropsch reaction. Mg(I) complexes have enabled multiple CO coupling reactions; however, their mechanisms are challenging to characterize due to strong ionic interactions and multiple competing pathways. Here, we performed automated reaction path network exploration for 2-, 3-, 4-, and 6-CO coupling reactions mediated by Mg(I) complexes using the single-component artificial force induced reaction (SC-AFIR) and the Δ-learning neural network potential methodologies to provide deeper understanding. These unbiased explorations reveal pathways for all experimentally observed products while uncovering a rich mechanistic landscape. While CO coupling steps for 2- and 3-CO coupling reactions are similar to earlier reports, the network uncovers new pathways for C-H activation in the 2-CO coupling reaction. SC-AFIR exploration of the 4-CO coupling reaction highlights competing reaction pathways, leading to both kinetically and thermodynamically controlled products. A key resting state for Mg complexes provides a rationale for related CO coupling in Al complexes with similar ligand environments. Intrinsic bond orbital (IBO) analysis shows that strong ionic Mg-O interactions facilitate the rare event of C-O cleavage in the 4-CO coupling reaction. The 6-CO coupling proceeds stepwise, contrasting earlier reports, with the Mo-center acting as an organizing nucleus that facilitates sequential CO coupling. The network also identifies several accessible channels for previously unidentified products. Overall, this study reveals pronounced mechanistic diversity in Mg(I)-mediated CO coupling and demonstrates how reaction path network exploration can resolve complex, multichannel reactivity in low-valent main-group systems.