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.