N-heterocyclic carbene-stabilized germa-acylium ion: reactivity and utility in catalytic CO2 functionalizations

Debotra Sarkar, Catherine Weetman, Sayan Dutta, Emeric Schubert, Christian Jandl, Debasis Koley, Shigeyoshi Inoue

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The first acceptor-free heavier germanium analogue of an acylium ion, [RGe(O)(NHC)2]X (R = MesTer = 2,6-(2,4,6-Me3C6H2)2C6H3; NHC = IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene; X = (Cl or BArF = {(3,5-(CF3)2C6H5)4B}), was isolated by reacting [RGe(NHC)2]X with N2O. Conversion of the germa-acylium ion to the first solely donor-stabilized germanium ester [(NHC)RGe(O)(OSiPh3)] and corresponding heavier analogues ([RGe(S)(NHC)2]X and [RGe(Se)(NHC)2]X) demonstrated its classical acylium-like behavior. The polarized terminal GeO bond in the germa-acylium ion was utilized to activate CO2 and silane, with the former found to be an example of reversible activation of CO2, thus mimicking the behavior of transition metal oxides. Furthermore, its transition-metal-like nature is demonstrated as it was found to be an active catalyst in both CO2 hydrosilylation and reductive N-functionalization of amines using CO2 as the C1 source. Mechanistic studies were undertaken both experimentally and computationally, which revealed that the reaction proceeds via an N-heterocyclic carbene (NHC) siloxygermylene [(NHC)RGe(OSiHPh2)].

Original languageEnglish
Pages (from-to)15403-15411
Number of pages9
JournalJournal of the American Chemical Society
Issue number36
Early online date10 Aug 2020
Publication statusPublished - 9 Sep 2020


  • catalytic CO2 functionalizations
  • transition metal oxides
  • mechanistic studies


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