Reactions of co-ordinated ligands. Part 21. Reaction of 3,3,3-trifluoroprop-1-yne with methyl- and benzyl-dicarbonyl(η-cyclopentadienyl)iron and of hexafluorobut-2-yne with tricarbonyl(1—3-η-2-methylallyl)cobalt. Crystal and molecular structure of [1—5-η-exo-1-acetyl-2,4,6-tris(trifluoromethyl)cyclohexadienyl](η-cyclopentadienyl)iron

Abstract

The u.v. irradiation of a hexane solution of 3,3,3-trifluoroprop-1-yne and [FeR(CO)₂(η-C₅H₅)](R = Me, CH₂C₆H₅, or C₃H₅) affords the vinyl complexes [Fe{C(CF₃)C(H)R}(CO)₂(η-C₅H₅)](R = Me, CH₂C₆H₅), or C₃H₅) arising from cis insertion of the acetylene, and η⁵-pyranyl complexes [Fe{[graphic ommitted](CF₃)}(–(η-C₅H₅)](R = Me or CH₂C₆H₅). In the case of the methyl and benzyl system, [1–5-η-exo-1-acyl-2,4,6-tris(trifluoromethyl)cyclohexadienyl](η-cyclopentadienyl) iron complexes are also formed. An X-ray determination of the molecular structure of the acetyl compound shows that the 3,3,3-trifluoroprop-1-yne molecules have linked head to tail to form a six-membered ring of envelope conformation, with five atoms coplanar and η⁵-bonded to the iron atom. The cyclopentadienyl ring is likewise η⁵-bonded to the iron and completes a parallel-plane sandwich. The sixth carbon atom of the C₆ ring bends away from the metal, and the acetyl group completes a tetrahedral arrangement around this atom, again bending away (exo configuration) in the same sense. The bond lengths in the planar portion of the C₆ ring suggest extensive delocalisation. The crystals are monoclinic, space group P2₁/n(no. 14) with Z= 4 in a unit cell of dimensions a= 13.025(3), b= 10.432(2), c= 12.503(2)Å, and β= 101.93(5)°. The structure has been solved by heavy-atom methods from 3 236 independent intensities measured on a fourcircle diffractometer and refined to R 0.056. The possible reaction paths available for the formation of these products are discussed. A reinvestigation of the reaction of hexafluorobut-2-yne with [Co(CO)₃(η³-2-MeC₃H₄)] has afforded only the two compounds [[graphic ommitted]CH₂}(CO)₃] and [[graphic ommitted]CH₂}(CO)₃] there being no evidence for the formation of a bis-insertion product.