Efficient solventless dehydrogenation of formic acid by a CNC-based rhodium catalyst

Hermosilla, Pablo (Universidad de Zaragoza) ; Urriolabeitia, Asier (Universidad de Zaragoza) ; Iglesias, Manuel ; Polo, Victor (Universidad de Zaragoza) ; Casado, Miguel A. (Universidad de Zaragoza)

Resumen: The complex (CNC)MesRh(PMe2Ph)]PF6 (1) has been found to be an effective catalyst for solventless formic acid (FA) dehydrogenation, affording exclusively H2 and CO2 as decomposition products. The effect of the addition of a base as a co-catalyst was studied, and it was found that HCOONa was the most efficient additive in terms of catalyst efficiency with a catalyst loading of 0.016 mol%, reaching TOFmax values up to 5869 h-1. Additionally, we observed that the addition of water dramatically increased the catalytic activity in FA dehydrogenation, yielding TOFmax values up to 10 150 h-1. Additionally, VT kinetic NMR experiments allowed us to estimate the activation energy (¿G‡ = 18.12 ± 1.17 kcal mol-1) of the FA dehydrogenation catalysed by 1. Stoichiometric NMR experiments, aimed to shed light on the nature of possible catalytic intermediates, allowed us to detect and further isolate the RhIII hydrido formate complex (CNC)MesRh(¿O-OC(O)H)(PMe2Ph)H]PF6 (2), which originates from an oxidative addition of FA to 1; additionally, we could detect a bis(hydrido) RhIII complex (CNC)MesRh(PMe2Ph)H2]PF6 (1-H2), which is another operative intermediate in the catalytic FA dehydrogenation by 1. DFT calculations performed on the catalytic FA dehydrogenation perfectly accounted for the gathered experimental data; the approach of a FA molecule to 1 leads to O-H oxidative addition producing the ¿O-formate intermediate 2, which subsequently undergoes a FA-assisted isomerization to the ¿H-formate species. Further hydride abstraction generates the dihydrido intermediate 1-H2, which releases H2 upon interaction with another FA molecule closing the catalytic cycle. The rate-limiting step in the catalytic process corresponds to the hydride abstraction step, which agrees with the KIE values estimated by NMR experiments. © 2022 The Royal Society of Chemistry

Idioma: Inglés

DOI: 10.1039/d2qi01056a

Año: 2022

Publicado en: Inorganic Chemistry Frontiers 9, 17 (2022), 4538 [10 pp]
ISSN: 2052-1545

Factor impacto JCR: 7.0 (2022)

Categ. JCR: CHEMISTRY, INORGANIC & NUCLEAR rank: 3 / 42 = 0.071 (2022) - Q1 - T1

Factor impacto CITESCORE: 10.1 - Chemistry (Q1)

Factor impacto SCIMAGO: 1.331 - Inorganic Chemistry (Q1)

Financiación: info:eu-repo/grantAgreement/ES/DGA-FSE/E42-20R
Financiación: info:eu-repo/grantAgreement/ES/MICINN/PGC2018-099383-B-I00
Financiación: info:eu-repo/grantAgreement/ES/MICINN/RTI2018-099136-A-I00

Tipo y forma: Artículo (PostPrint)

Área (Departamento): Área Química Inorgánica (Dpto. Química Inorgánica)
Área (Departamento): Área Química Física (Dpto. Química Física)