A. Antinolo et al., SYNTHESIS, ELECTROSYNTHESIS AND STRUCTURAL STUDIES OF BIS(SILYLCYCLOPENTADIENYL)NIOBIUM COMPLEXES WITH ACETYLENE LIGANDS, Journal of organometallic chemistry, 481(1), 1994, pp. 27-35
The reduction of [Nb(eta(5)-C(5)H(4)SiMe(3))(2)Cl-2] (1) with one equi
valent of sodium amalgam (10%) in the presence of acetylenes yields [N
b(eta(5)-C(5)H(4)SiMe(3))(2)Cl(eta(2)-RC(1) = CR(2))], (R(1) = H, R(2)
= COOMe, 3c; R(1) = Me, R(2) = COOMe, 3d; R(1)= R(2) = COOMe, 3e). Th
e structural characterization of these compounds has been carried out
by NMR spectroscopy. The reduction of the (acetylene)niobium(V) comple
xes [Nb(eta(5)-C(5)H(4)SiMe(3))(2)Cl(eta(2) R(1)C = CR(2))] with one e
quivalent of sodium amalgam (10%) gives the paramagnetic niobium(IV) c
omplexes [Nb(eta(5)-C(5)H(4)SiMe(3))(2)(eta(2)-R(1)C = CR(2))] (R(1) =
R(2) = Ph, 4a; R(1) = H, R(2) = Ph, 4b; R(1) = H, R(2) = COOMe, 4c; R
(1) = Me, R(2) = COOMe, 4d; R(1) = R(2) = COOMe, 4e), which have been
characterized by ESR spectroscopy. However, electroreduction of 1 in t
he presence of the acetyIenes gives the complexes 3 or 4 depending bot
h on the nature of the acetylene and on the experimental conditions. I
n the electrolysis of 1 in the presence of acetylenes c or d a slow pr
oduction of 4e and 4d, respectively, occurs to yield the alkenyl compl
exes [Nb(eta(5)-C(5)H(4)SiMe(3))(2)Cl(eta(1)-R(1)C = CHR(2))], 4'c and
4'd. Finally, the addition of HCl to solutions of 4a gives a mixture
of 1 and cis-stilbene.