Synthesis, Reactivity, Electrochemical Study, and Crystal Structures of (η⁵:η⁵-(C₅H₃CO₂Me)₂)Mo₂(CO)₆

Abstract

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.

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

“…6 and 12 show stretching modes at higher frequencies than the analogous unsubstituted species, which is due to the electron-withdrawing properties of the carbomethoxy substituent in the Fv and Cp rings, respectively. On the other hand, the bands observed at 1905 and 1848 cm -1 in the IR spectra of 5 − 8 are very similar to those shown by the lithium salt Li 2 [(η 5 :η 5 -C 5 H 3 CO 2 Me) 2 Mo 2 (CO) 6 ], which supports their ionic nature.…”

“…The ionic nature of 5 − 8 is in accordance with the two signals observed (triplet and multiplet) at ca. 4.80 and 5.50 ppm attributable to the anionic half, by analogy with the lithium salt previously prepared . The 31 P NMR spectra show a single signal for all compounds in the characteristic range of the cis isomer. , …”

“…The molecular structure determination of 4 shows that the Mo(CO) 3 I units are on opposite sides of the Fv ligand. In the parent molecule (η 5 :η 5 -C 5 H 3 CO 2 Me) 2 Mo 2 (CO) 6 , 2 , both Mo(CO) 3 I units are on the same side of the Fv ligand . Some structural differences between 1 , 2 , and 4 arise as a result of the new orientation of the Mo(CO) 3 I units.…”

“…Me 3 NO was sublimed prior to use and stored under argon. The compounds trans - and cis -(η 5 :η 5 -C 5 H 3 CO 2 Me) 2 Mo 2 (CO) 6 ( 1 and 2 ), Li 2 (η 5 :η 5 -C 5 H 3 CO 2 Me) 2 Mo 2 (CO) 6 , Na(η 5 -C 5 H 4 CO 2 Me), (η 5 :η 5 -C 10 H 8 )Mo 2 (CO) 6 , and (η 5 :η 5 -C 10 H 8 )W 2 (CO) 6 were prepared according to literature procedures, ,, and all reagents were used without further purification unless otherwise noted.…”

“…The synthesis of (η 5 :η 5 -(C 5 H 3 CO 2 Me) 2 )Mo 2 (CO) 6 has been recently reported . Two pure isomers trans ( 1 ) and cis ( 2 ) were easily isolated by thin-layer chromatography (TLC), and each of them has been well-characterized.…”