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)(6)Fe2Se2{mu-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 [Fe-2(CO)(6)Se-2{mu-(Co)(3)Cr(eta(5)-C-5(R)(R')(Ph)(OEt)}] (8a R = H, R' = Ph; 8b R, R' = Ph; 8c R = H, R' = (CH2)(3)-CH3; and 8d R, R' = C2H5) are formed in 72-79% yield. The corresponding SSe analogue [(Co)(6)Fe2SSe{mu-C(Ph)=C-C(OEt)=Cr(CO)(5)}] (7) reacts with phenylacetylene or diphenylacetylene to form [Fe-2(CO)(6)SSe{mu-C(H)C(O)C(H)=C(eta(6)-C6H6Cr(CO)(3))C(Ph)}] (9a) or [Fe-2(CO)(6)-SSe{mu-C(H)C(O)C(Ph)=C(eta(6)-C6H5Cr(CO)(3))C(PhP}] (9b) in high yields (82% and 85%). All new compounds have been characterized by IR and H-1, C-13, and Se-77 NMR spectroscopy, and structural types were unequivocally established by crystallographic analysis of compounds 8b and 9b