Annulation reactions of Fischer Carbene complexes tethered on a chalcogen-stabilized iron carbonyl cluster: dependence of reaction pathway on chalcogen atom

Abstract

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 [Fe₂(CO)₆SSe{ μ-C(H)C(O)C(H)=C(η⁶-C₆H₅Cr(CO)₃)C(Ph)}] (9a) or [Fe₂(CO)₆SSe{ μ-C(H)C(O)C(Ph)=C(η⁶-C₆H₅Cr(CO)₃)C(Ph)}] (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.