As/Se-units as building blocks in cobalt complexes containing the C5Me4Et ligand. Crystal structure of (eta(5)-C5Me4Et)Co(eta(4)-As6Se)

The reaction of Cp-2*Co-2(CO)(2) 1 (Cp* = C5Me4Et) with equimolar amounts o f As4Se4 was investigated at different temperatures and compared to the rea ction of 1 with As4S4. In boiling toluene the formation of Cp-2*Co2As2Se3 ( 4-Se) and Cp-3*Co3As2Se4 (5-Se) was observed, whereas in boiling xylene in addition to 4-Se and 5-Se Cp*CoAs6Se (7) was formed. Spectroscopic investig ations show that the structures of 4-Se and 5-Se are analogous to those of the known compounds Cp-2*Co2As2S3 (4-S) and Cp-3*Co3As2S4 (5-S). As 7 is th e first complex derived from selenium substituted E-7(3-) (E = P, As, Sb) Z intl ions, an X-ray diffraction analysis was carried out showing that it co nsists of a norbornadiene-like cage of the main group elements to which a C p*Co fragment is coordinated via four As atoms as a four-electron ligand. ( C) 1998 Elsevier Science Ltd. All rights reserved.