New indenyl phosphinooxazoline complexes of iron and their catalytic activity in the Mukaiyama aldol reaction

New phosphinooxazoline (PHOX) η⁵-indenyl complexes of iron were synthesized and applied as catalysts in the Mukaiyama aldol reaction. Reaction of three different PHOX ligands with Fe(η⁵-Ind)I(CO)₂] afforded the iodide salts of three complexes of the general formula Fe(η⁵-Ind)(CO)(PHOX)]⁺ in 73-81% isolated yields. The molecular structure of one of the new complexes was determined, revealing a pseudo octahedral coordination geometry about the iron center. The iron complexes are catalytically active in the Mukaiyama aldol reaction between aldehydes and 1-(tert-butyldimethylsilyloxy)-1-methoxyethene to give the corresponding aldol adducts (3 mol % catalyst, 15 min, room temperature, 48-83% isolated yields). A previously synthesized iron complex of the general formula Fe(η⁵-Cp)(CO)(PHOX)]⁺ was found to be catalytically active in the title reaction as well, but needed three hours at room temperature to convert the starting materials to the products.