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

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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.

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