Low-temperature N2 binding to two-coordinate L2Fe(0) enables reductive trapping of L2FeN2(-) and NH3 generation.
The 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)2Fe(I)][BAr(F)4], [(CAAC)2Fe(0)], and [(CAAC)2Fe(-I)N2](-) were all found to be active for the reduction of dinitrogen to ammonia upon treatment with KC8 and HBAr(F)4⋅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](-) .
Division of Chemistry and Chemical Engineering, California Institute of Technology (USA).
Gaël
G
Ung
Jonas C
JC
Peters
D000641:Ammonia / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D013696:Temperature
D005290:Ferric Compounds; D000641:Ammonia
carbenes; coordination modes; iron; nitrogen fixation; structure elucidation