Studies on the reactions of ferrocenylphenylacetylene and diferrocenyl-acetylene with (η5-cyclopentadienyl)dicarbonylcobalt, and an x-ray crystallographic determination of one of the products: (η5-cyclopentadienyl)(η4-1,3-diferrocenyl-2,4-diphenylcyclobutadiene)cobalt

The reaction of (η5-C5H5)Co(CO)2 and diferrocenylacetylene has been shown to produce the mixed sandwich complex (η5-cyclopentadienyl)(η4-tetraferrocenylcyclobutadiene)cobalt in 83% yield. A similar reaction between (η5-C5H5)Co(CO)2 and ferrocenylphenylacetylene produces two structural isomers, (η5-cyclopentadienyl)(η4-1,2-diferrocenyl-3,4-diphenylcyclobutadiene)cobalt and (η5-cyclopentadienyl)(η4-1,3-diferrocenyl-2,4-diphenylcyclobutadiene)cobalt, in 78% combined yield. The structures of these two products have been inferred from proton NMR and mass spectral studies, and unequivocally established by means of a single crystal X-ray diffraction investigation of the latter isomer. (η5-cyclopentadienyl)(η4-1,3-diferrocenyl-2,4-diphenylcyclobutadiene) cobalt, c41H33CoFe2, is monoclinic, P21/c with a = 10.551(3), b = 16.345(2), c = 19.796(3) Å and B = 93.19°. However, the unit cell was found to contain 2 hexane molecules in addition to 4 parent molecules to yield a calculated density of 1.441 g/cm−3. The measured density was 1.44(2) g/cm−3. Intensity data were gathered by the 8–28 scan method with an automated 4-circle diffractometer (CAD-4) yielding 7315 reflections (10,450 scanned) greater than 3Ï. Refinement by full matrix least squares led to a final R of 0.039. The cyclobutadiene ring is square with average bond length of 1.462(5) Å. However, the ring is not quite planar, one of the carbons being 0.035 Å out of the plane formed by the other three. Other features of the structure are regular with the ferrocene C5 rings being in the eclipsed conformation.