High Spin Iron–Phosphinidene and Arsinidene Complexes With Attenuated Metal–Ligand Multiple Bond Character

The MEH₂ salts (M = Na, K; E = P, As) react with high spin (S = 2) PhB(AdIm)₃FeCl (PhB(AdIm)₃^– = tris(3-adamantylimidazol-2-ylidene)phenylborate) to afford the corresponding PhB(AdIm)₃FePH₂ and PhB(AdIm)₃FeAsH₂ complexes. Remarkably, these complexes can be deprotonated by benzyl potassium in the presence of equimolar 18-crown–6 or 2,2,2-crypt to provide the parent phosphinidene and arsinidene complexes, [PhB(AdIm)₃FePH]^– and [PhB(AdIm)₃FeAsH]^–. Structural and spectroscopic characterization, combined with computational investigations, provide evidence for multiconfigurational electronic structures in which the metal–ligand multiple bond character is attenuated by the high spin iron(II) center. Initial reactivity studies reveal the nucleophilic character of the pnictogenidene ligands, which provide phosphinophosphinidene and phosphinoarsinidene products with a chlorodiazaphospholidine electrophile.