Sidney E Creutz1, Jonas C Peters. 1. Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
Abstract
While recent spectroscopic studies have established the presence of an interstitial carbon atom at the center of the iron-molybdenum cofactor (FeMoco) of MoFe-nitrogenase, its role is unknown. We have pursued Fe-N2 model chemistry to explore a hypothesis whereby this C-atom (previously denoted as a light X-atom) may provide a flexible trans interaction with an Fe center to expose an Fe-N2 binding site. In this context, we now report on Fe complexes of a new tris(phosphino)alkyl (CP(iPr)3) ligand featuring an axial carbon donor. It is established that the iron center in this scaffold binds dinitrogen trans to the C(alkyl)-atom anchor in three distinct and structurally characterized oxidation states. Fe-C(alkyl) lengthening is observed upon reduction, reflective of significant ionic character in the Fe-C(alkyl) interaction. The anionic (CP(iPr)3)FeN2(-) species can be functionalized by a silyl electrophile to generate (CP(iPr)3)Fe-N2SiR3. (CP(iPr)3)FeN2(-) also functions as a modest catalyst for the reduction of N2 to NH3 when supplied with electrons and protons at -78 °C under 1 atm N2 (4.6 equiv NH3/Fe).
While recent spectroscopic studies have established the presence of an interstitial n class="Chemical">carbon atom at the center of the iron-molybdenum cofactor (FeMoco) of MoFe-nitrogenase, its role is unknown. We have pursued Fe-N2 model chemistry to explore a hypothesis whereby this C-atom (previously denoted as a light X-atom) may provide a flexible trans interaction with an Fe center to expose an Fe-N2binding site. In this context, we now report on Fe complexes of a new tris(phosphino)alkyl (CP(iPr)3) ligand featuring an axial carbondonor. It is established that the iron center in this scaffold binds dinitrogen trans to the C(alkyl)-atom anchor in three distinct and structurally characterized oxidation states. Fe-C(alkyl) lengthening is observed upon reduction, reflective of significant ionic character in the Fe-C(alkyl) interaction. The anionic (CP(iPr)3)FeN2(-) species can be functionalized by a silyl electrophile to generate (CP(iPr)3)Fe-N2SiR3. (CP(iPr)3)FeN2(-) also functions as a modest catalyst for the reduction of N2 to NH3 when supplied with electrons and protons at -78 °C under 1 atm N2 (4.6 equiv NH3/Fe).
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