Jump to main content
Jump to site search


Mechanistic Insights into HCO2H Dehydrogenation and CO2 Hydrogenation Catalyzed by Ir(Cp*) Containing Tetrahydroxy Bipyrimidine Ligand: The Role of Sodium and Proton Shuttle

Abstract

The mechanism of HCO2H dehydrogenation catalyzed by [IrCp*(H2O)(bpymO4H4)]2+, (bpymO4H4 = 2,2ʹ,6,6ʹ-tetrahydroxy-4,4ʹ-bipyrimidine) was investigated using density functional theory. The relative free energy profiles at various protonation states, corrected to pH 3.5 and pH 7.6, suggested that Na+ together with the ortho-oxyanion of bipyrimidine facilitates the formation of the Ir-HCO2, subsequent hydride transfer, and H2 formation. HCO2H was found to be a more effective proton shuttle than H2O for H2 formation. Under experimental conditions, the highest catalytic reactivity was found at pH 3.5-4.0, where both HCO2Na and HCO2H are present. At lower pH, at low formate concentration, HCO2H dehydrogenation tends to proceed via a Na+ independent pathway, involving a higher energy barrier. At higher pH, although Na+ can mediate hydride transfer and H2 formation, the low amount of HCO2H results in H2O as the proton shuttle, which involves a higher energy barrier than HCO2H proton shuttle. That is, the catalytic activity of HCO2H dehydrogenation by the proton-responsive Ir complexes at different pH values is influenced by the protonation state, involvement of Na+, and the availability of HCO2H as a proton shuttle. For the hydrogenation of CO2 at pH 8.3, the rate determining step is heterolytic cleavage of H2 mediated by Na+, via a HCO3- proton shuttle. Our results demonstrate the importance of alkali metal ions in the design of catalysts for efficient, reversible, CO2 conversion.

Back to tab navigation

Supplementary files

Publication details

The article was received on 10 Aug 2018, accepted on 05 Nov 2018 and first published on 06 Nov 2018


Article type: Paper
DOI: 10.1039/C8DT03283A
Citation: Dalton Trans., 2018, Accepted Manuscript
  •   Request permissions

    Mechanistic Insights into HCO2H Dehydrogenation and CO2 Hydrogenation Catalyzed by Ir(Cp*) Containing Tetrahydroxy Bipyrimidine Ligand: The Role of Sodium and Proton Shuttle

    P. Surawatanawong and T. Wonglakhon, Dalton Trans., 2018, Accepted Manuscript , DOI: 10.1039/C8DT03283A

Search articles by author

Spotlight

Advertisements