Synthesis of heteroleptic bis-phosphine bis-NHC iron (0) complexes: a strategy to enhance small molecule activation

We report the synthesis of heteroleptic iron complexes supported by both a bis-phosphine ligand (depe) and a bis-NHC ligand. The mixed ligand sets provide access to iron (0) adducts of N₂ and CO that are highly activated, in comparison to homoleptic (i.e. Fe(depe)₂L) variants. Computational and experimental studies revealed the mixed ligand set distorts the geometric and electronic structure to yield an unusually basic iron. Although protonation occurred at Fe, silylation of the Fe(0)N₂ complex afforded a highly activated silyldiazenido [FeNNSiMe₃]⁺ complex.