Low-Temperature N-2 Binding to Two-Coordinate L2Fe0 Enables Reductive Trapping of L2FeN2- and NH3 Generation

摘要

The two-coordinate [(CAAC)(2)Fe] complex [CAAC=cyclic (alkyl)(amino)carbene] binds dinitrogen at low temperature (T<-80 degrees C). The resulting putative three-coordinate N-2 complex, [(CAAC)(2)Fe(N-2)], was trapped by one-electron reduction to its corresponding anion [(CAAC)(2)FeN2](-) at low temperature. This complex was structurally characterized and features an activated dinitrogen unit which can be silylated at the -nitrogen atom. The redox-linked complexes [(CAAC)(2)Fe-I][BAr4F], [(CAAC)(2)Fe-0], and [(CAAC)(2)Fe-IN2](-) were all found to be active for the reduction of dinitrogen to ammonia upon treatment with KC8 and HBAr(4)(F)2Et(2)O at -95 degrees C [up to (3.4 +/- 1.0)equivalents of ammonia per Fe center]. The N-2 reduction activity is highly temperature dependent, with significant N-2 reduction to NH3 only occurring below -78 degrees C. This reactivity profile tracks with the low temperatures needed for N-2 binding and an otherwise unavailable electron-transfer step to generate reactive [(CAAC)(2)FeN2](-).