ELECTROCHEMISTRY OF [MO2CP2(CO)(4)(MU-N(2) - ETA(3)-HC-C-C(R1)(R2))](- R1 = ME, R2 = ME, PH) - CONTROL OF THE REDUCTION PROCESS (2-ELECTRONVS ONE-ELECTRON) BY THE SUBSTITUENTS R1 AND R2 - EHMO RATIONALIZATION() COMPLEXES (R1 = H, R2 = H, ME, ET, FC )
Jf. Capon et al., ELECTROCHEMISTRY OF [MO2CP2(CO)(4)(MU-N(2) - ETA(3)-HC-C-C(R1)(R2))](- R1 = ME, R2 = ME, PH) - CONTROL OF THE REDUCTION PROCESS (2-ELECTRONVS ONE-ELECTRON) BY THE SUBSTITUENTS R1 AND R2 - EHMO RATIONALIZATION() COMPLEXES (R1 = H, R2 = H, ME, ET, FC ), Organometallics, 16(21), 1997, pp. 4645-4656
The electrochemical reduction of Mo2Cp2(CO)(4){mu-eta(2):eta(3)-HC=C-C
(R1)(R2)}](+) complexes has been investigated by cyclic voltammetry, c
ontrolled-potential electrolysis, and coulometry. On the cyclic voltam
metry time scale, the complexes with R1 = H, R2 = H (1(+)): Me (2(+)),
Et (3(+)) undergo an irreversible or a quasi-reversible one-electron
reduction whereas the analogues with R1 = H, R2 = Fc (4(+)) and R1 Me,
R2 = Me (5(+)) and Ph (6(+)) reduce in a single-step, reversible or q
uasi-reversible, two-electron process. Two different chemical reaction
s are involved in the overall reduction mechanism. The first chemical
step is assigned as a structural rearrangement, responsible for slowin
g down the heterogeneous electron transfer. Extended Huckel MO calcula
tions indicate that in the case of the complexes with R1 = H, R2 = Pc
and R1 = Me, R2 = Me or Ph, a small increase in the distance between o
ne metal center and the carbon of the C(R1)(R2) group could trigger th
e two-electron transfer process. The second chemical reaction leading
to the final product(s) of the reduction involves radical species, eve
n when a two-electron transfer is observed by cyclic voltammetry. The
final products formed in these processes have been identified either b
y H-1 NMR spectroscopy of the compounds extracted from the catholyte a
fter controlled-potential electrolyses or from a comparison of their c
haracteristic redox potentials with those of authentic samples. The na
ture of the final product(s), either a dimer or mu-alkyne and mu-enyne
complexes, is also dependent on the nature of R1 and R2.