(Carbonyl)iron-selenolates: New synthetic methods and reactions with electrophiles. Crystal structures of [(CO)(6)Fe-2(mu-SeR)(2)]; R = Me3SiCH2 and p-O2NC6H4CH2, {(CO)(6)Fe-2[mu-eta(2)-Se,Se '-o-(SeCH2C6H4CH2Se)]}, and [(CO)(6)Fe-2(mu-SeFe(CO)(2)cp)(2)]

The reactions of Fe(CO)(5) or Fe-3(CO)(12) with NaBEt3H or KB[CH(CH3)C2H5]( 3)H, respectively and treatment of the resulting carbonylates M2Fe(CO)(4), M = Na, K with elemental selenium in appropriate ratios lead to the formati on of M-2[Fe-2(CO)(6)(mu-Se)(2)]. Subsequent reactions with organo halides or the complex fragment cpFe(CO)(2)(+), cp = eta(5)-C5H5 afforded the selen olato complexes [Fe-2(CO)(6)(mu-SeR)(2)], R = CH2SiMe3 (1), CH2Ph (2), p-CH 2C6H4NO2 (3), o-CH2C6H4CH2 (4) and cpFe(CO)(2)(+) (5) in moderate to good y ields. A similar reaction employing Ru-3(CO)(12), Se and p-O2NC6H4CH2Br lea ds to the formation of the corresponding organic diselenide. The X-ray stru ctures of 1, 3, 4 and 5 were determined and revealed butterfly structures o f the Fe2Se2 cores. The substituents in 1, 3 and 5 adopt different conforma tions depending on their steric demand. In 4, the conformation is fixed bec ause of the chelate effect of the ligand. The Fe-Se bond lengths lie in the range 235 to 240 pm, with corresponding Fe-Fe bond lengths of 254 to 256 p m. The Se-77 NMR data of the new complexes are discussed and compared with the corresponding data of related complexes.