An S = ½ iron complex featuring N₂, thiolate, and hydride ligands: Reductive elimination of H₂ and relevant thermochemical Fe-H parameters

Abstract

Believed to accumulate on the Fe sites of the FeMo-cofactor (FeMoco) of MoFe-nitrogenase under turnover, strongly donating hydrides have been proposed to facilitate N₂ binding to Fe and may also participate in the hydrogen evolution process concomitant to nitrogen fixation. Here, we report the synthesis and characterization of a thiolate-coordinated Fe^(III)(H)(N₂) complex, which releases H₂ upon warming to yield an Fe^(II)–N₂–Fe^(II) complex. Bimolecular reductive elimination of H₂ from metal hydrides is pertinent to the hydrogen evolution processes of both enzymes and electrocatalysts, but well-defined examples are uncommon and usually observed from diamagnetic second- and third-row transition metals. Kinetic data obtained on the HER of this ferric hydride species are consistent with a bimolecular reductive elimination pathway, arising from cleavage of the Fe–H bond with a computationally determined BDFE of 55.6 kcal/mol.

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