NOVEL PRODUCTS FROM REACTIONS OF LI[(MU-CO)(MU-RS)FE2(CO)(6)] SALTS WITH ETHOXYACETYLENE

Reactions of Li[(mu-CO)(mu-RS)Fe-2(CO)(6)] salts with ethoxyacetylene followed by reaction of the anionic intermediate thus generated with acetyl or benzoyl chloride gave an Fe-2(CO)(6) 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(O(2)CR(1))= <-> =C(OEt)CH=C(O(2)CR(1))-. The structure of the complex in which R = t-Bu and R(1) = CH3 was determined by X-ray diffraction. Extended Huckel MO calculations for a model system, Fe-2(CO)(6)(mu-SH)(mu-C3H3), led to its description in terms of an ideally delocalized C-3 bridge coupled to the iron atoms of the (mu-HS)Fe-2(CO)(6) unit by two strong sigma-bonds and by moderate pi-back-bonding. Protonation of the anionic intermediate with trifluoroacetic acid gave the alpha,beta-unsaturated bridging acyl complexes (mu-EtOC(=CH2)C=O)(mu-RS)Fe-2(CO)(6) (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 (mu-EtOC=CH2)(mu-RS)Fe-2(CO)(6).