Precursors to dinitrogenreduction: structures and reactivity of trans-[Fe(DMeOPrPE)2(η2-H2)H]+ and trans-[Fe(DMeOPrPE)2(N2)H]+

Abstract

trans-[Fe(DMeOPrPE)₂(H₂)H]⁺ and trans-[Fe(DMeOPrPE)₂(N₂)H]⁺ (DMeOPrPE = 1,2-bis(dimethoxypropylphosphino)ethane) were synthesized and their structures determined by X-ray crystallography. These complexes are important species in a dinitrogen reduction scheme involving protonation of an iron(0) dinitrogen complex to produce ammonia. The rates of substitution of the coordinated H₂ and N₂ molecules with acetonitrile were monitored in a variety of organic solvents. The coordinated N₂ substituted ∼6 times faster than H₂, but surprisingly the solvent had little effect on the observed rates. The results suggest that the H₂ molecule in trans-[Fe(DMeOPrPE)₂(H₂)H]⁺ does not participate in hydrogen bonding to the bulk solvent, as was previously observed in the analogous Ru complex. The deprotonation of trans-[Fe(DMeOPrPE)₂(N₂)H]⁺ to yield Fe(DMeOPrPE)₂N₂ was investigated in the presence of a variety of anions, and it was found that the anion facilitates the reaction through an ion-pairing interaction in which the anion removes electron density from the hydride ligand.