in tetrahydrofuran under N2; addn. of α-imino ketone to stirred suspn. of Fe2(CO)9 in THF, stirring for 3 h at room temp.; evapn., column chromy. (SiO2, pentane for Fe3(CO)12, 7:1 pentane/Et2O for Fe2(CO)6 complex, 2:3 Et2O/CH2Cl2 for Fe2(CO)4 complex), crystn. frompentane at -60°C (Fe2(CO)6 complex) and 2:3 pentane/CH2Cl2 (Fe2(CO)4 complex;