Exploiting the Liquid Phase to Enhance the Cross-Coupling of Alcohols over Nanoporous Gold Catalysts

Journal Article · Tue Dec 14 00:00:00 EST 2021 · ACS Catalysis

DOI:https://doi.org/10.1021/acscatal.1c04383· OSTI ID:1845281

Eagan, Nathaniel M. ^[1]; Luneau, Mathilde ^[2]; Friend, Cynthia M. ^[2]; Madix, Robert J. ^[2]

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1. Harvard Univ., Cambridge, MA (United States); Harvard
2. Harvard Univ., Cambridge, MA (United States)

Controlling selectivity in the cross-coupling of two similar compounds is a classic challenge in heterogeneous catalysis. Here it is shown that the phase in which the catalysis is performed has a dramatic impact on the selectivity of the oxidative coupling of alcohols to esters over unsupported nanoporous gold catalysts, affording nearly optimal cross-coupling to a single ester at equimolar concentrations in the liquid. Operation in the liquid vs the gas phase affects 1) the relative C-H activation rates of methoxy and 1-propoxy, 2) the fraction of C-H activation which leads to esters vs aldehydes, and 3) the fraction of esters which result from cross-coupling vs self-coupling. While activation of the critical adsorbed reactive alkoxy intermediate is faster for 1-propoxy than methoxy in both phases, the liquid phase is more effective in coupling the resulting aldehyde with adsorbed methoxy or 1-propoxy to yield an ester. Additionally, operation in the liquid phase promotes cross-coupling to methyl propionate, whereas in the gas-phase self-coupling of 1-propanol to propyl propionate is favored. The promotion of self-coupling in the gas phase results from the stabilization of larger alkoxides on the surface by Au-alkyl van der Waals forces. However, such forces do not appear dominant in the liquid phase, as evidenced by similar cross-coupling selectivities of methanol with ethanol, 1-propanol, and 1-butanol. Introducing steric hindrance into the higher alcohol (i.e., 2-methyl-1-propanol) further promotes cross-coupling. Here, this promotion is attributed to a kinetic preference for an aldehyde to couple with less-hindered alkoxides. Altogether, these findings demonstrate that alcohol cross-coupling selectivities are strongly impacted by the phase in which the catalysis is conducted, thus altering the phase provides opportunities for selective and efficient chemical syntheses.

• Research Organization: Harvard Univ., Cambridge, MA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0012573
• OSTI ID: 1845281
• Journal Information: ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 1 Vol. 12; ISSN 2155-5435
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
alcohol coupling
alcohols
cross coupling reaction
gold
liquid phase
liquids
methyl ester
organic compounds
selectivity