Annulation Reactions of Fischer Carbene Complexes Tethered on a Chalcogen-Stabilized Iron Carbonyl Cluster: Dependence of Reaction Pathway on Chalcogen Atom

When a benzene solution containing the Fischer carbene complex [(CO)6Fe2Se2{μ-C(Ph)C−C(OEt)Cr(CO)5}] (6) and phenylacetylene, diphenylacetylene, 1-hexyne, or 3-hexyne is
subjected to reflux, the substituted cyclopentadienylchromium complexes [Fe2(CO)6Se2{μ-(CO)3Cr(η5-C5(R)(R‘)(Ph)(OEt)}] (8a R = H, R‘ = Ph; 8b R, R‘ = Ph; 8c R = H, R‘ = (CH2)3CH3; and 8d R, R‘ = C2H5) are formed in 72−79% yield. The corresponding SSe analogue
[(CO)6Fe2SSe{μ-C(Ph)C−C(OEt)Cr(CO)5}] (7) reacts with phenylacetylene or diphenylacetylene to form (9a) or (9b) in high yields (82% and 85%). All
new compounds have been characterized by IR and 1H, 13C, and 77Se NMR spectroscopy,
and structural types were unequivocally established by crystallographic analysis of
compounds 8b and 9b.