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ChemRxiv224_SI.pdf (6.65 MB)
Activation of Ammonia and Hydrazine by Electron Rich Fe(II) Complexes Supported by a Dianionic Pentadentate Ligand Platform Through a Common Terminal Fe(III) Amido Intermediate
Preprints are manuscripts made publicly available before they have been submitted for formal peer review and publication. They might contain new research findings or data. Preprints can be a draft or final version of an author's research but must not have been accepted for publication at the time of submission.
submitted on 17.11.2020, 21:27 and posted on 18.11.2020, 12:43by Lucie Nurdin, Yan Yang, Peter Neate, Warren Piers, Laurent Maron, Michael L. Neidig, Jian-Bin Lin, Benjamin
We report the use of electron rich iron complexes supported by a dianionic diborate
pentadentate ligand system, B2Pz4Py, for the coordination and activation of ammonia (NH3) and
hydrazine (NH2NH2). For ammonia, coordination to neutral (B2Pz4Py)Fe(II) or cationic
[(B2Pz4Py)Fe(III)]+ platforms leads to well characterized ammine complexes from which
hydrogen atoms or protons can be removed to generate, fleetingly, a proposed (B2Pz4Py)Fe(III)-
NH2 complex (3Ar-NH2). DFT computations suggest a high degree of spin density on the amido
ligand, giving it significant aminyl radical character. It rapidly traps the H atom abstracting agent
2,4,6-tri-tert-butylphenoxy radical (ArO•) to form a C-N bond in a fully characterized product
(2Ar), or scavenges hydrogen atoms to return to the ammonia complex (B2Pz4Py)Fe(II)-NH3 (1ArNH3). Interestingly, when (B2Pz4Py)Fe(II) is reacted with NH2NH2, a fully characterized bridging
diazene complex, 4Ar, is formed along with ammonia adduct 1Ar-NH3 as the spectroscopically
observed (-78˚C) (B2Pz4Py)Fe(II)-NH2NH2-Fe(II)( B2Pz4Py) dimer (1Ar)2-NH2NH2 is allowed to
warm to room temperature. Experimental and computational evidence is presented to suggest
that (B2Pz4Py)Fe(II) induces reductive cleavage of the N-N bond in hydrazine to produce the
Fe(III)-NH2 complex 3Ar-NH2, which abstracts H• atoms from (1Ar)2-NH2NH2 to generate the
observed products. All of these transformations are relevant to proposed steps in the ammonia
oxidation reaction, an important process for the use of nitrogen-based fuels enabled by
abundant first row transition metals.