Iron(II) N-heterocyclic carbene complexes in catalytic one-pot Wittig reactions: Mechanistic insights

- First reported Fe(II) NHC complex applied in catalytic aldehyde olefination.
- High olefin yields (90%) with excellent E/Z selectivity (>94%).
- Mechanistic studies reveal catalytic formation of ylide, then Wittig-type reaction.

An iron(II) N-heterocyclic carbene (NHC) complex is applied as catalyst for aldehyde olefination with ethyl diazoacetate (EDA) in the presence of triphenylphosphine. The reaction leads to high olefin yields with very good E-selectivities. The key step of the reaction is the catalytic in situ generation of a phosphorus ylide. Mechanistic studies reveal two possible pathways for the formation of the Wittig reagent with respect to the carbene source being the metal carbene (NHC)FeIVCH(CO2Et), and phosphazine, Ph3PNNCH(CO2Et). Based on the experimental observations a new mechanism for the transformation of phosphazine is proposed.

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