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Triggering N2 uptake via redox-induced expulsion of coordinated NH3 and N2 silylation at trigonal bipyramidal iron

Abstract

The biological reduction of N2 to give NH3 may occur by one of two predominant pathways in which nitrogenous NxHy intermediates, including hydrazine (N2H4), diazene (N2H2), nitride (N3−) and imide (NH2−), may be involved. To test the validity of hypotheses on iron's direct role in the stepwise reduction of N2, model systems for iron are needed. Such systems can test the chemical compatibility of iron with various proposed NxHy intermediates and the reactivity patterns of such species. Here we describe a trigonal bipyramidal Si(o-C6H4PR2)3Fe–L scaffold (R = Ph or i-Pr) in which the apical site is occupied by nitrogenous ligands such as N2, N2H4, NH3 and N2R. The system accommodates terminally bound N2 in the three formal oxidation states (iron(0), +1 and +2). N2 uptake is demonstrated by the displacement of its reduction partners NH3 and N2H4, and N2 functionalizaton is illustrated by electrophilic silylation.

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Figure 1: Synthetic scheme for the generation of Fe–N2+, Fe–N2 and Fe–N2 (3, 4b, 5 and 5′).
Figure 2: CV behaviour of (SiPi-Pr3)Fe(N2) (4b).
Figure 3: Solid-state structures of 3, 5 and 5′.
Figure 4: Solid-state structures of {6b}{OTf}, 7a, N2H4B(C6F5)3 and 9b.
Figure 5: Synthesis and characterization of 10 and 11.
Figure 6: Synthesis and characterization of 12.
Figure 7: Zero-field Mössbauer spectra.

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Acknowledgements

We acknowledge the National Institutes of Health (GM-070757). Funding for the Massechussetts Institute of Technology Department of Chemistry Instrumentation Facility was provided in part by the National Science Foundation (NSF) (CHE-0234877). P. Mueller provided assistance with XRD analyses. N.P.M. received an NSF graduate fellowship. We thank R.H. Holm and T.A. Betley at Harvard University for providing us with access to a Mössbauer spectrometer.

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Y.L., N.P.M. and J.C.P. conceived and designed the experiments, Y.L. and N.P.M. performed the experiments and Y.L. and J.C.P. co-wrote the paper.

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Correspondence to Jonas C. Peters.

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Supplementary information

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Supplementary information (PDF 9061 kb)

Supplementary information

Crystallographic information for compound 1a (CIF 25 kb)

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Crystallographic information for compound 1b (CIF 22 kb)

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Crystallographic information for compound 3 (CIF 37 kb)

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Crystallographic information for compound 4b (CIF 23 kb)

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Crystallographic information for compound 5 (CIF 16 kb)

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Crystallographic information for compound 5′ (CIF 46 kb)

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Crystallographic information for compound 6a·BArF (CIF 75 kb)

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Crystallographic information for compound 6a·OTf (CIF 49 kb)

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Crystallographic information for compound 6b·OTf (CIF 25 kb)

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Crystallographic information for compound 7a (CIF 46 kb)

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Crystallographic information for compound 7b (CIF 65 kb)

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Crystallographic information for compound 8 (CIF 31 kb)

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Crystallographic information for compound 9a (CIF 34 kb)

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Crystallographic information for compound 9b (CIF 35 kb)

Supplementary information

Crystallographic information for compound 10 (CIF 23 kb)

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Crystallographic information for compound 11 (CIF 43 kb)

Supplementary information

Crystallographic information for compound 12 (CIF 20 kb)

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Lee, Y., Mankad, N. & Peters, J. Triggering N2 uptake via redox-induced expulsion of coordinated NH3 and N2 silylation at trigonal bipyramidal iron. Nature Chem 2, 558–565 (2010). https://doi.org/10.1038/nchem.660

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