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

Abstract

AbstractThe two‐coordinate [(CAAC)2Fe] complex [CAAC=cyclic (alkyl)(amino)carbene] binds dinitrogen at low temperature (T<−80 °C). The resulting putative three‐coordinate N2 complex, [(CAAC)2Fe(N2)], was trapped by one‐electron reduction to its corresponding anion [(CAAC)2FeN2]− 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)2FeI][BArF4], [(CAAC)2Fe0], and [(CAAC)2Fe−IN2]− were all found to be active for the reduction of dinitrogen to ammonia upon treatment with KC8 and HBArF4⋅2 Et2O at −95 °C [up to (3.4±1.0) equivalents of ammonia per Fe center]. The N2 reduction activity is highly temperature dependent, with significant N2 reduction to NH3 only occurring below −78 °C. This reactivity profile tracks with the low temperatures needed for N2 binding and an otherwise unavailable electron‐transfer step to generate reactive [(CAAC)2FeN2]−.