Reduction and Condensation of Aldehydes by the Isolated Cofactor of Nitrogenase

Isolated nitrogenase cofactors can reduce CO, CN^-, and CO₂ to short-chain hydrocarbons in reactions driven by a strong reductant. Here, we use activity analyses and isotope labeling experiments to show that formaldehyde and acetaldehydes can be reduced as-is or reductively condensed into alkanes and alkenes by the isolated cofactor of Mo-nitrogenase in the presence of Eu^II-diethylenetriamine pentaacetate (DTPA). Further, we demonstrate that aldehydes can be condensed with CO by the isolated cofactor under the same reaction conditions, pointing to aldehyde-derived species as possible intermediates of nitrogenase-catalyzed CO reduction. Our deuterium labeling experiments suggest the formation of a cofactor-bound hydroxymethyl intermediate upon activation of the formaldehyde, as well as the release of C₂H₄ as a product upon β-hydride elimination of an acetaldehyde-derived hydroxyethyl intermediate. These findings establish the reductive condensation of aldehydes as a previously unobserved reactivity of a biogenic catalyst while at the same time shed light on the mechanism of enzymatic CO reduction and C-C bond formation, thereby providing a useful framework for further exploration of the unique reactivity and potential applications of nitrogenase-based reactions.