Mixed-Valence Iron Complexes Containing End-On Bridging Cyaphide Ions.

Iron cyanide compounds are among the oldest known synthetic coordination compounds, dating back to the early 18th century. By contrast, iron complexes of the cyaphide ion (C≡P-)─a heavy valence isoelectronic analog of the cyanide ion─are unknown. Herein we report the synthesis of highly stable mono- and bis-cyaphide complexes of iron(II), namely Fe(depe)2(Cl)(CP) and Fe(depe)2(CP)2 (depe = 1,2-bis(diethylphosphino)ethane). These iron(II) cyaphide complexes are capable of further coordination to iron(I) in a hitherto unknown linear coordination geometry, affording the conjugated multimetallic mixed-valence complexes [{Fe(depe)2}2(μ-CP)(N2)][BArF4]2 and [{Fe(depe)2}3(μ-CP)2][OTf]2.