Recent Development about the Use of Pyrocarbonates as Activator in Organic Synthesis: A Review

Synthesis and Structure of Pb[C2O5]: An Inorganic Pyrocarbonate Salt

We have synthesized Pb[C₂O₅], an inorganic pyrocarbonate salt, in a laser-heated diamond anvil cell (LH-DAC) at 30 GPa by heating a Pb[CO₃] + CO₂ mixture to ≈2000(200) K. Inorganic pyrocarbonates contain isolated [C₂O₅]^2- groups without functional groups attached. The [C₂O₅]^2- groups consist of two oxygen-sharing [CO₃]^3- groups. Pb[C₂O₅] was characterized by synchrotron-based single-crystal structure refinement, Raman spectroscopy, and density functional theory calculations. Pb[C₂O₅] is isostructural to Sr[C₂O₅] and crystallizes in the monoclinic space group P2₁/c with Z = 4. The synthesis of Pb[C₂O₅] demonstrates that, just like in other carbonates, cation substitution is possible and that therefore inorganic pyrocarbonates are a novel family of carbonates, in addition to the established sp² and sp³ carbonates.

Sr[C2O5] is an Inorganic Pyrocarbonate Salt with [C2O5]2- Complex Anions

The synthesis of a novel type of carbonate, namely of the inorganic pyrocarbonate salt Sr[C₂O₅], which contains isolated [C₂O₅]^2--groups, significantly extends the crystal chemistry of inorganic carbonates beyond the established sp²- and sp³-carbonates. We synthesized Sr[C₂O₅] in a laser-heated diamond anvil cell by reacting Sr[CO₃] with CO₂. By single crystal synchrotron diffraction, Raman spectroscopy, and density functional theory (DFT) calculations, we show that it is a pyrocarbonate salt. Sr[C₂O₅] is the first member of a novel family of inorganic carbonates. We predict, based on DFT calculations, that further inorganic pyrocarbonates can be obtained and that these will be relevant to geoscience and may provide a better understanding of reactions converting CO₂ into useful inorganic compounds.