A Nonclassical Dihydrogen Adduct of <i>S</i> = ¹/₂ Fe(I)

We have exploited the capacity of the “(SiPiPr3)Fe(I)” scaffold to accommodate additional axial ligands and characterized the mononuclear S = 1/2 H2 adduct complex (SiPiPr3)FeI(H2). EPR and ENDOR data, in the context of X-ray structural results, revealed that this complex provides a highly unusual example of an open-shell metal complex that binds dihydrogen as a ligand. The H2 ligand at 2 K dynamically reorients within the ligand-binding pocket, tunneling among the energy minima created by strong interactions with the three Fe–P bonds.