Cyclisation of diferrocenylbutadiyne dicobalt hexacarbonyl mono-adduct to novel ferrocenotropones

Treatment of 1,4-diferrocenyl-1,3-butadiyne dicobalt hexacarbonyl complex with trifluoroacetic acid resulted in cyclisation with concomitant CO insertion to give the green 2,3-ferroceno-7-ferrocenyl-4,5-dehydrotropone dicobalt hexacarbonyl, which in turn was converted by trifluoroacetic acid to red 2,3-ferroceno-7-ferrocenyltropone. The first step implied the involvement of a second dicobalt hexacarbonyl complex as a CO source. The molecular structures of the novel tropones were determined by X-ray analysis.