Low‐Temperature N2 Binding to Two‐Coordinate L2Fe0 Enables Reductive Trapping of L2FeN2− and NH3 Generation

Gaël Ung, Jonas C. Peters

doi:10.1002/anie.201409454

<jats:title>Abstract</jats:title><jats:p>The two‐coordinate [(CAAC)<jats:sub>2</jats:sub>Fe] complex [CAAC=cyclic (alkyl)(amino)carbene] binds dinitrogen at low temperature (T<−80 °C). The resulting putative three‐coordinate N<jats:sub>2</jats:sub> complex, [(CAAC)<jats:sub>2</jats:sub>Fe(N<jats:sub>2</jats:sub>)], was trapped by one‐electron reduction to its corresponding anion [(CAAC)<jats:sub>2</jats:sub>FeN<jats:sub>2</jats:sub>]<jats:sup>−</jats:sup> at low temperature. This complex was structurally characterized and features an activated dinitrogen unit which can be silylated at the β‐nitrogen atom. The redox‐linked complexes [(CAAC)<jats:sub>2</jats:sub>Fe<jats:sup>I</jats:sup>][BAr<jats:sup>F</jats:sup><jats:sub>4</jats:sub>], [(CAAC)<jats:sub>2</jats:sub>Fe<jats:sup>0</jats:sup>], and [(CAAC)<jats:sub>2</jats:sub>Fe<jats:sup>−I</jats:sup>N<jats:sub>2</jats:sub>]<jats:sup>−</jats:sup> were all found to be active for the reduction of dinitrogen to ammonia upon treatment with KC<jats:sub>8</jats:sub> and HBAr<jats:sup>F</jats:sup><jats:sub>4</jats:sub>⋅2 Et<jats:sub>2</jats:sub>O at −95 °C [up to (3.4±1.0) equivalents of ammonia per Fe center]. The N<jats:sub>2</jats:sub> reduction activity is highly temperature dependent, with significant N<jats:sub>2</jats:sub> reduction to NH<jats:sub>3</jats:sub> only occurring below −78 °C. This reactivity profile tracks with the low temperatures needed for N<jats:sub>2</jats:sub> binding and an otherwise unavailable electron‐transfer step to generate reactive [(CAAC)<jats:sub>2</jats:sub>FeN<jats:sub>2</jats:sub>]<jats:sup>−</jats:sup>.</jats:p>

Low‐Temperature N<sub>2</sub> Binding to Two‐Coordinate L<sub>2</sub>Fe<sup>0</sup> Enables Reductive Trapping of L<sub>2</sub>FeN<sub>2</sub><sup>−</sup> and NH<sub>3</sub> Generation

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