The Diphenylacetylene Reaction with Tricarbonylbis(η2-cis-cyclooctene)iron in the Presence or Absence of Carbon Monoxide

Known to be a facile irontricarbonyl transfer reagent, (η²-cis-C₈H₁₄)₂Fe(CO)₃ 1 transfers its Fe(CO)₃ unit to a variety of ligands at low temperature. Stirring a THF mixture of 1 and PhC=CPh under N₂(g) at ?60 °C for 1 h then at room temperature overnight provides mainly a flyover-bridge product -CPh=CPhC(0)-CPh=CPh-]Fe₂(CO)₆ 2 with the organic bridge on diiron core in a complicated μ-(1,2,5-η³:1,4,5-η³) fashion. The keto fragment in 2 comes presumably from the decomposition of 1 that liberates CO. However, stirring a THF mixture of 1 and PhC=CPh under CO(g) at ?60 °C for 3 h then at room temperature overnight results in -C(0)CPh=CPhC(0)-]Fe(CO)₄ 3, a compound not isolated in the earlier thermal or photochemical reactions of PhC=CPh with ironcarbonyl. The X-ray structure determinations for both 2 and 3 have been performed.