Tilt the Molecule and Change the Chemistry: Mechanism of S‐Promoted Chemoselective Catalytic Hydrogenation of Crotonaldehyde on Cu(111)

Abstract

The chemoselective hydrogenation of a,b-unsaturated carbonyl compounds to form unsaturated alcohols is challenging, fundamentally interesting, and important both in the research laboratory and on a technical scale, as these materials are valuable and versatile intermediates in the production of fine chemicals and pharmaceuticals. Thermodynamics favors hydrogenation of the C=C bond to form the (unwanted) saturated aldehyde or ketone as shown in Scheme 1, which refers to the particular case of crotonaldehyde. Thus chemoselective C = O hydrogenation is a demanding process that requires the manipulation of kinetic effects by means of a suitable catalyst.A variety of supported metal-particle catalysts (including Pt, Pd, Cu, Ag, Au, Ir, and Os) that exhibit a wide range of chemoselectivity have been investigated for this purpose, [1] though very little has emerged in terms of fundamental understanding. Theoretical studies [2] suggest that the adsorption geometry of the reactant molecule may be a key Scheme 1. Possible hydrogenation products of crotonaldehyde.

Molecular Lifting, Twisting, and Curling during Metal-Assisted Polycyclic Hydrocarbon Dehydrogenation

“…Finally, the control of molecular tilt in PAHs could tailor their chemical reactivity, by activating or inhibiting specific reactions that are usually catalyzed by the surface, as reported for example in the case of different carbonyl compounds, more specifically aldehydes, on transition metal substrates. 40,41…”

“…The use of nanostructured surfaces, such as those formed by a high density of monoatomic steps or vacancies, could be a possibility to reduce the geometrical degree of freedom forced by the hexagonal surface of Ir(111), with C 3 v symmetry, and achieve an easier control of the reaction parameters. Finally, the control of molecular tilt in PAHs could tailor their chemical reactivity, by activating or inhibiting specific reactions that are usually catalyzed by the surface, as reported, for example, in the case of different carbonyl compounds, more specifically aldehydes, on transition metal substrates. , …”

“…40,41 ■ ASSOCIATED CONTENT * S Supporting InformationThe Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.5b12504.Angle-resolved photoemission data, additional DFTcalculated adsorption configurations, C−C bond length histograms, and microkinetic reaction model (PDF)Movie showing the structural changes of the coronene molecule during the dehydrogenation process as obtained by the Nudged Elastic Band calculations (MPG)…”

Highly Selective Catalysts for the Hydrogenation of Unsaturated Aldehydes: A Review

“…This enhanced selectivity was ascribed to the increased electron density of Pt by the promotion with NaCl. Chiu et al , studied Cu(111) modified with sulfur for the hydrogenation of CRAL in an ultrahigh vacuum chamber. The NEXAFS spectrum was used to estimate the CC and CO tilt angles, with respect to the metal surface.…”