Low Temperature N2 Binding to 2-coordinate L2Fe0 Enables Reductive Trapping of L2FeN2− and NH3 Generation.

摘要

The 2-coordinate (CAAC)2Fe complex [CAAC = cyclic (alkyl)(amino)carbene] binds dinitrogen at low temperature (T < −80 °C). The resulting putative 3-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 that can be silylated at the β-nitrogen. The redox linked complexes (CAAC)2Fe^IBAr^F24, (CAAC)2Fe⁰ and [(CAAC)2Fe^−IN2]⁻ were all found to be active for the reduction of dinitrogen to ammonia upon treatment with reductant (KC8) and acid (HBAr^F24·2Et2O) at −95 °C (up to 3.4 ±1.0 equivalent 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]⁻.