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, 6:4 pentane/Et2O for Fe2(CO)6 complex), crystn. from pentane at -60°C (Fe2(CO)6 complex);