Cyclisation of diferrocenylbutadiyne dicobalt hexacarbonyl mono-adduct to novel ferrocenotropones

Treatment of 1,4-diferrocenyl-1,3-butadiyne dicobalt hexacarbonyl complex (1) [CARN: 178388-65-3] with trifluoroacetic acid resulted in cyclisation with concomitant CO insertion to give the green 2,3-ferroceno-7-ferrocenyl-4,5-dehydrotropone dicobalt hexacarbonyl (2), which in turn was converted by trifluoroacetic acid to red 2,3-ferroceno-7-ferrocenyltropone (3). The first step implied the involvement of a second dicobalt hexacarbonyl complex as a CO source. The molecular structures of 2 and 3 were determined by single crystal X-ray analysis, and pairs of enantiomers with different conformations were observed in 3.