Coupling Reactions of Ferrocenylacetylene with Mononuclear Metal Carbonyls Fe(CO)5 and M(CO)6 (M = Mo, W): Synthesis and Characterization of [Fe(CO)2{η5-2,5-Fc2C5H2CO}C(Fc)CH], [Fe(CO)2{η2:η2-2,5-Fc2C4H2Fe(CO)3}-μ-CO], [Fe(CO)3{η2:η2-2,5-Fc2C4H2CO}], 1,2,4-Triferrocenylbenzene, 2,5-Diferrocenylthiophene, and 2,5-Diferrocenylselenophene

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Thermolysis of a benzene solution containing Fe(CO) 5 and ferrocenylacetylene yielded three new compounds: [Fe(CO) 2 {η 5 -2,5-Fc 2 C 5 H 2 CO}C(Fc)=CH] (1), [Fe(CO) 2 {η 2 :η 2 -2,5-Fc 2 C 4 H 2 -Fe(CO) 3 }-μ-CO] (2), and [Fe(CO) 3 {η 2 :η 2 -2,5-Fc 2 C 4 H 2 CO}] (3). When a benzene solution containing ferrocenylacetylene and M(CO) 6 (M = Mo, W) was refluxed, 1,2,4-triferrocenylbenzene (4) was formed. In contrast to the reaction of ferrocenylacetylene with Fe(CO) 5 , which leads to cyclization with insertion of a CO molecule, in the reaction with M(CO) 6 no insertion of CO takes place during cyclization. However, if the reactions with M(CO) 6 are carried out in the presence of S 8 -powder or Se-powder, insertion of these chalcogen atoms during cyclization does take place and 2,5-diferrocenylthiophene (5) and 2,5-diferrocenylselenophene (6) are formed respectively, along with 4. All new compounds were characterized by IR and 1 H and 1 3 C NMR spectroscopy. Structures of 1-5 were established by single-crystal X-ray crystallography.