Modifying catalytic sustainability: aromaticity, conceptual DFT and steric mapping

Abstract

Catalytic hydrogenation, is a crucial process in the chemical and pharmaceutical industries. Traditional catalysts for this process often use noble metals like palladium, ruthenium, and iridium.

Despite their effectiveness, these metals pose significant drawbacks, including limited availability, high cost, and environmental and toxicity concerns. Consequently, there has been a shift

toward using more sustainable and abundant first-row transition metals, with iron complexes

emerging as a promising alternative.

The research on iron complexes aims to enhance the efficiency of these catalysts by modifying

the substituents on the cyclopentadienone structure of Kno¨olker-type iron catalysts. Previous

studies have indicated that such modifications can lower energetic barriers, thereby improving

the reactivity of the catalysts. The study focuses on understanding how these structural changes

impact the activation of the catalyst and the rate-determining step (rds) in the catalytic cycle.

In this context, the activation involves the release of a CO ligand facilitated by trimethylamineN -oxide, which generates the active species essential for the catalytic process. The rds is the

hydrogenation step, mediated by molecular hydrogen, and it is notably energy-demanding. Solvents like ethanol or water can assist this step by reducing the energy barrier.

The results reveal that altering the substituents on the cyclopentadienone and the annulatedring structure significantly reduces the energy barriers, thereby enhancing catalytic efficiency.

Computational analyses, including evaluations of electronic and geometric indices such as atomic

charges, Mayer Bond Orders, and Fukui functions, provide insights into the reactivity and

interaction patterns within the catalyst structure. Steric maps offer visual representations of

the catalyst’s spatial arrangement and interactions with substrates, further clarifying the effects

of structural modifications on catalytic performance.

Overall, the study demonstrates that structural modifications in iron-based catalysts can directly influence the energy barriers of the catalytic cycle, thereby affecting the efficiency of the

hydrogenation process and the conditions under which the synthesis of the complexes can occur