Identity of the Silyl Ligand in an Iron Silyl Complex Influences Olefin Hydrogenation: An Experimental and Computational Study

In this study, we explore the selective synthesis of iron silyl complexes using the reaction of an iron mesityl complex (^MesCCC)FeMes(Py) with various hydrosilanes. These resulting iron silyl complexes, (^MesCCC)Fe(SiH₂Ph)(Py)(N₂), (^MesCCC)Fe(SiMe₂Ph)(Py)(N₂), and (^MesCCC)Fe[SiMe(OSiMe₃)₂](Py)(N₂), serve as effective precatalysts for olefin hydrogenation. The key to their efficiency in catalysis lies in the specific nature of the silyl ligand attached to the iron center. Experimental observations, supported by density functional theory (DFT) simulations, reveal that the catalytic performance correlates with the relative stability of dihydrogen and hydride species associated with each iron silyl complex. The stability of these intermediates is crucial for efficient hydrogen transfer during the catalytic cycle. The DFT simulations help to quantify these stability factors, showing a direct relationship between the silyl ligand's electronic and steric properties and the overall catalytic activity. Complexes with certain silyl ligands exhibit better performance due to the optimal balance between the stability and reactivity of the key active catalyst. This work highlights the importance of ligand design in the development of iron-based hydrogenation catalysts.