Gauging the donor strength of iron(0) complexes via their N-heterocyclic carbene gold(i) adducts

Abstract

We isolate and characterize the gold(I)–iron(0) adducts [(ⁱPr₂-bimy)Au–Fe(CO)₃(PMe₃)₂][BAr^F₄] and [Au–{Fe(CO)₃(PMe₃)₂}₂][BAr^F₄] (ⁱPr₂-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene, BAr^F₄ = tetrakis(pentafluorophenyl)borate). DFT analysis reveals that the gold–iron interaction in [(ⁱPr₂-bimy)Au–Fe(CO)₃(PMe₃)₂][BAr^F₄] is predominantly a σ-donation from iron to gold. We further extend this class of compounds to include [(ⁱPr₂-bimy)Au–Fe(CO)₃(PR₃)₂][BAr^F₄] (PR₃ = PPh₃, PCy₃, PCyPh₂, PMePh₂, PMe₂Ph, P(4-C₆H₄F)₃) and [(ⁱPr₂-bimy)Au–Fe(CO)₄(PPh₃)][BAr^F₄] and correlate the ⁱPr₂-bimy carbenic ¹³C NMR signal with the relative donor strength of the iron(0) ligand. This approach allows for a fast and simple approach to gauge relative donor strength of Fe(0) donors.