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 a cetyl or benzoyl chloride gave an Fe-2(CO)(6) complex that contained t he thiolate ligand as well as a novel resonance-stabilized bridging vi nylcarbene 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 calculati ons for a model system, Fe-2(CO)(6)(mu-SH)(mu-C3H3), led to its descri ption in terms of an ideally delocalized C-3 bridge coupled to the iro n atoms of the (mu-HS)Fe-2(CO)(6) unit by two strong sigma-bonds and b y moderate pi-back-bonding. Protonation of the anionic intermediate wi th 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-r ay crystal structure of the complex in which R = t-Bu was determined. These complexes lost CO in THF solution at room temperature, giving (m u-EtOC=CH2)(mu-RS)Fe-2(CO)(6).