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Reactions of Li[@-CO)@-RS)Fez(C0)6] salts with ethoxyacetylene followed by reaction of the anionic intermediate thus generated with acetyl or benzoyl chloride gave a n Fez(CO)s complex that contained the thiolate ligand as well as a novel resonance-stabilized bridging vinylcarbene ligand which incorporated the acetylene and an original CO ligand that may be written as -C(OEt)=CHC(OZCR')= -=C(OEt)CH-C(OzCR')-. The structure of the complex in which R = t-Bu and R1 = CH3 was determined by X-ray diffraction. Extended Huckel MO calculations for a model system, F~z(CO)~@-SH)@-C~H~), led to its description in terms of a n ideally delocalized C3 bridge coupled to the iron atoms of the @-HS)Fe~(co)6 unit by two strong a-bonds and by moderate mback-bonding. Protonation of the anionic intermediate with trifluoroacetic acid gave the a,/kinsaturated bridging acyl complexes @- (R = t-Bu, Et). The X-ray crystal structure of the complex in which R = t-Bu was determined. These complexes lost CO in THF solution at room temperature, giving Cu-EtOC=CHz)@-RS)Fez(C0)6. E~OC(=CHZ)C=O)@-RS)F~Z(CO)~