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

Abstract

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.

Zwitterionic Organometallates

“…[{η 1 :η 6 -C 6 H 5 (TiCp 2 Cl)}Cr(CO) 3 ]), [92] zwitterionic bimetallic complexes of Group 6 metals are found in the fulvalene series. Homodinuclear complexes, in which the metals exhibit different CO vs. phosphane substitution patterns, can be prepared by several methods (A, [93] B, [94] or C [95] ) from (fulvalene)Mo 2 (CO) 6 and basic phosphanes. After metalmetal bond cleavage, the steric repulsion between the metal centers overrides the electrostatic attraction and results in a 180°rotation of the cyclopentadienyl metal moieties, which, in turn, leads to a trans arrangement of the opposite charges with respect to the cyclopentadienyl plane.…”