New General Synthetic Strategy of Fulvalene Homodinuclear Zwitterions. Electrochemical Behavior of (η:5η5-(C5H3CO2Me)2)Mo2(CO)6R2 (R = I, Me)

The reaction of Li2[(η5:η5-(C5H3CO2Me)2)Mo2(CO)6] (from trans-(η5:η5-(C5H3CO2Me)2)Mo2(CO)6) (1) with MeI yields (η5:η5-(C5H3CO2Me)2)Mo2(CO)6Me2 (3). The reaction of cis-(η5:η5-(C5H3CO2Me)2)Mo2(CO)6 (2) with I2 leads to the formation of (η5:η5-(C5H3CO2Me)2)Mo2(CO)6I2 (4). The X-ray structure of 4 has been determined. The reactions of 1 with P-donor nucleophiles (PPhMe2, PPh2Me, P(n-Bu)3, and PMe3) and (η5:η5-(C10H8)M2(CO)6 (M = Mo and W) with PMe3, in the presence of 1 equiv of Me3NO, produce CO labilization and formation of the dinuclear zwitterions (η5:η5-(C5H3CO2Me)2)Mo2(CO)5L2 and (η5:η5-(C10H8)M2(CO)5(PMe3)2 (M = Mo and W) 5, 6, 7, 8, 9, and 10, respectively). The dimer [(η5-C5H4CO2Me)Mo(CO)3]2 (11) was obtained by reaction of Mo(CO)6 with sodium carbomethoxy cyclopentadienide in THF followed by oxidation with ferric sulfate. The reaction of 11 with PPh2Me in the presence of 1 equiv of Me3NO gives the disproportionation species [(η5-C5H4CO2Me)Mo(CO)2(PPh2Me)2 +][η5-C5H4CO2Me)Mo(CO)3 -] (12). The electrochemical study of 3 and 4 is reported. Two distinct cathodic waves are observed in the voltammetric reduction of 4, the less negative one with a coupled anodic peak at high sweep rates in PC.