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New catalyst transforms carbon dioxide into commodity chemicals

A magnesium hydride complex pairs with a boron Lewis acid to selectively hydrosilylate CO2 and convert it to formaldehyde

by Stephen K. Ritter
January 1, 2018 | A version of this story appeared in Volume 96, Issue 1

Credit: Courtesy of Gerard Parkin
A structure shows a new magnesium benzimidazole hydride catalyst.
Credit: Courtesy of Gerard Parkin

A Columbia University research team has prepared a magnesium catalyst that can efficiently convert carbon dioxide to precursors for commodity chemicals such as formaldehyde. Carbon dioxide is usually thought of as an essential molecule for photosynthesis and as a greenhouse gas that helps control Earth’s climate. But because CO2 is abundant and cheap, it also offers much potential as a renewable carbon source for synthesizing chemicals and fuels. The catch is that the gas is not very reactive until it overreacts, so chemists need to come up with catalysts that selectively functionalize CO2 to produce targeted products. One approach is hydrosilylation, but control of the product distribution by high-priced precious-metal catalysts at the hot temperatures they require is challenging and may result in complete reduction of CO2 to methane. The new catalysts prepared by Columbia’s Michael Rauch and Gerard Parkin instead use less costly zinc or magnesium and work selectively at room temperature. In particular, the researchers found that a magnesium benzimidazole hydride treated with the Lewis acid B(C6F5)3 produces a reactive cation-anion pair that coordinates CO2 and transfers the hydride to carbon, efficiently creating a formate intermediate (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.7b10776). The formate group can be removed from the catalyst by reaction with different hydrosilanes in the presence of B(C6F5)3 to make various products. For example, triphenylsilane (Ph3SiH) generates a bis(silyl)acetal that is a protected form of formaldehyde, whereas phenylsilane (PhSiH3) generates methane.

A reaction scheme depicts a method for converting carbon dioxide to commodity chemicals using a magnesium catalyst.
A new magnesium hydride catalyst, when paired with the potent Lewis acid B(C6F5)3, produces a reactive species that coordinates CO2 and transfers the hydride to the Lewis acid, efficiently creating a formate intermediate that can be selectively rendered into different products depending on the silane used.


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