Title:
Redox reactivity and comprehensive synthetic chemistry of the
perchloroditungstate [W(2)(mu-Cl)(3)Cl(6)](n-) (n = 3, 2, 1) anions in
organic media
Abstract:
The catalytic reactivity of the perchloroditungstate anions
[W(2)(mu-Cl)(3)Cl(6)](n-) (n=3, 2, 1) [n=3, 2 (W(2)(6+),a’(2)
e’(4)); n = 2, 3 (W(2)(7+), a’(2) e’(3)); n = 1, 4 (W(2)(8+), a’(2)
e’(2))] in organic media remains unexplored, despite the facile redox
activity of the W(2)(n+) core (n = 4, 6-8), due to, among other reasons,
the lack of simple and efficient methods for their synthesis. The
preparation of salts of 2 with the bulky organic cations [(n)Bu(4)N(+)
(TBA(+), a); Ph(4)P(+) (TPP(+), b)] can be achieved in high yield from
the room temperature reduction Of WCl(4) with Na/Hg in toluene (similar
to 90%), or from the reaction Of W(CO)6 with Me(3)SiCl in boiling
chlorobenzene (74%). Their oxidized counterparts 3a,b can be isolated
in high yield directly from the oxidative decarbonylation Of W(CO)6 with
1,2-dichloroethane in the presence of TBACl or TPPCl in boiling
chlorobenzene, or indirectly from the facile one-electron oxidation of
2a,b induced by (a) HCl((g)) in organic aprotic solvents (CH(2)Cl(2),
THF, MeCN) or in biphasic media (aqueous HCl 6-12 M/CH(2)Cl(2)); (b)
Lewis acids (SnCl(2), AlCl(3) in CH(2)Cl(2): (c) various metal halide
oxidants (FeCl(3), CuCl(2), HgCl(2)) in organic media (CH(2)Cl(2), THF,
MeCN); and (d) carbon tetrachloride in solution (CH(2)Cl(2), CCl(4)) or
in the solid state (2a,b/CCl(4)). The redox chemistry (chemical or
electrochemical) of the complexes in organic media, as well as their
UV-Vis, ESI-MS, CV and EPR spectra are also reported. Examination of 2b
by cyclic voltammetry in CH(2)Cl(2) gives two reversible waves at -0.741
and -0.021 V versus Fc(+)/Fc, which are related spectroelectrochemically
to the following successive one-electron processes: W(2)(6+) -> W(2)(7+)
-> W(2)(8+). Thus, the synthesis of 3b can be accomplished by bulk
electrolysis of 2b at 0.750V. Whereas 2a,b do not react anaerobically
with PhCH(2)OH at ambient temperature, complexes 3a,b are reduced to
2a,b producing a mixture of PhCHO and PhCH(2)Cl. The facile 2/3 redox
chemistry and the capability of 3 in oxidizing PhCH(2)OH makes this
redox couple functional and of potential utility in catalytic oxidations
of organic substrates. (C) 2008 Elsevier Ltd. All rights reserved.
