A bonding evolution theory study on the catalytic Noyori hydrogenation reaction

ABSTRACT

The electronic rearrangements involved in Noyori hydrogenation reactions with double bonds (ethene and formaldehyde) are analysed using the bonding evolution theory. The study and analysis of the changes on the electron localisation function topology along a given reaction path reveals fluxes of electron density, allowing to unambiguously identify the main chemical events happening along the chemical reactions. This analysis shows that the first hydrogen transfer (with hydride character) occurs before the transition state (TS), while the second hydrogen transfer (with proton character) takes places after having reached the TS. The lower energy barrier found for formaldehyde over ethene is explained by two reasons. First, the hydride transfer is favoured for the C = O bond over C = C due to the electrophilic character of the carbon atom. Second, a negatively charged CH₃–X (X = CH₂, O) hidden intermediate is formed in the proximities of the TS region. The oxygen atom is able to stabilise this negatively charged species more effectively than the CH₂ group due to its higher electronegativity and the presence of V(O) lone pairs. The obtained analysis explains and rationalises catalyst chemoselectivity (C = O vs. C = C). Finally, a curly arrow representation diagram accounting for the electronic rearrangements is proposed on the basis of BET results.

GRAPHICAL ABSTRACT

KEYWORDS:

• DFT calculations
• organometallic chemistry
• electron localisation function (ELF)
• catastrophe theory
• bonding evolution theory

Acknowledgements

All authors gratefully acknowledge the resources from the supercomputers ‘Memento’ and ‘Terminus’, technical expertise and assistance provided by the Institute for Biocomputation and Physics of Complex Systems (BIFI) – Universidad de Zaragoza. J. M. thankfully acknowledges Spanish MECD for an FPU fellow (FPU14/06003). R. L. acknowledges ED388 for a PhD grant.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Ministerio de Ciencia, Innovacion y Universidades [grant number CTQ2015-67366-P].