Reaction of ethynediyl, butadiynediyl and ethynyl iron complexes, ( η5-C 5R 5)(CO) 2Fe–(CC) n–X [X=Fe( η5-C 5R 5)(CO) 2, H; R 5=Me 5, Me 4Et; n=1, 2], with Fe 2(CO) 9 leading to polynuclear C 2 and C 4 complexes

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Polynuclear C 2 and C 4 cluster compounds are prepared by treatment of the iron complexes containing μ-C 2 (ethynediyl), μ-C 4 (butadiynediyl) and C 2H (ethynyl) ligands with Fe 2(CO) 9. The ethynediyl complex ( η 5-C 5Me 5)(CO) 2Fe–CC–Fe( η 5-C 5Me 5)(CO) 2 gives the tetrairon dicarbide complex, ( μ 4-C 2)Fe 4( η 5-C 5Me 5) 2(CO) 9, which shows dynamic behavior by way of reversible scission and recombination of the Fe–Fe bonds. Reaction of the butadiynediyl complex, ( η 5-C 5Me 5)(CO) 2Fe–CC–CC–Fe( η 5-C 5Me 5)(CO) 2, affords tetranuclear nona- and decacarbonyl cluster compounds depending on the reaction conditions. The nonacarbonyl cluster compound formed exclusively in benzene adopts a normal acetylide cluster type structure and one of the two CC functional groups remains unreacted, but the decacarbonyl cluster isolated as a minor product from the reaction in THF consists of a μ 3- η 3-propargylidene diiron core and a ketene functional group, which should be formed by addition of an Fe 2 unit followed by migration of CO to the terminal carbon atom of the C 4 bridge. In contrast, reactions of polyynyl complexes are found to be less selective. Reaction of ( η 5-C 5Me 5)(CO) 2Fe–CC–H results in the formation of a low yield mixture of products, of which the p-quinone complex, c-2,5-[Fe( η 5-C 5Me 5)(CO) 2] 2–C 6H 2O 2, has been isolated and characterized by X-ray crystallography, though ( η 5-C 5Me 5)(CO) 2Fe–CC–CC–H merely gives an intractable reaction mixture.