The reaction of a dicarbomethoxydihydrofulvalene solution with Mo(CO)6 leads to the formation of two isomers of (η5:η5-(C5H3CO2Me)2)Mo2(CO)6 (1 and 2). The X-ray structure of both compounds has been determined. Reaction of 2 with LiEt3BH yields Li2[(η5:η5-(C5H3CO2Me)2)Mo2(CO)6] (3), and this with Hg(CN)2 results in the insertion of Hg into the Mo−Mo bond giving (η5:η5-(C5H3CO2Me)2)Mo2(CO)6Hg (4). The electrochemical study of 1−4 is reported. The two-electron reduction of 1 and 2, through an ECE mechanism, leads to the dianions. This reduction takes place at a significantly less negative potential than for the unsubstituted fulvalene (η5:η5-C10H8)Mo2(CO)6 (5) due to the electron-withdrawing properties of the carbomethoxy substituents. The oxidation of 1 and 2 is also affected by the substituents, taking place at a more positive potential than 5. The reduction of 4 yields the dianion 2 2- and liberates Hg.

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