New catalyst transforms carbon dioxide into commodity chemicals

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.