Cobaltocene reduction of LMoVIO2(SPh)
complexes yielded extremely dioxygen-sensitive
cobaltocenium
salts of the cis-dioxo-Mo(V) radical anions
cis-[LMoVO2(SPh)]-,
while sodium acenaphthalenide reduction of
LaMoVIO2(SPh) yielded a complex sodium salt
containing
[LaMoVO2(SPh)]-
[L = hydrotris(3,5-dimethylpyrazol-1-yl)borate (La),
hydrotris(3-isopropylpyrazol-1-yl)borate (Lb), or
hydrotris(3,5-dimethyl-1,2,4-triazol-1-yl)borate
(Lc)].
Crystals of
[CoCp2][LcMoVO2(SPh)]·toluene
were orthorhombic, space group Pbca, with a =
17.695(3) Å, b =
19.490(3) Å, c = 21.925(4) Å, V =
7561(2) Å3 for Z = 8. The structure,
refined using a full-matrix least-squares
procedure and 2269 data, converged with R = 0.067
(R
w = 0.067). In the distorted octahedral
anion, the metrical
parameters of the cis-MoVO2 fragment
[Mo−O = 1.742(9) Å, O−Mo−O = 112.1(4)°] are
significantly larger than
those of LcMoVIO2(SPh)
[average Mo−O = 1.700(6) Å, O−Mo−O =
103.9(2)°]. 18O-Substitution of
[CoCp2][La,bMoVO2(SPh)] permitted the assignment of
bands at ca. 870 and 770 cm-1 to the
νs and νas modes, respectively,
of
the cis-MoVO2 fragment. Freshly
prepared solutions of
[CoCp2][LMoVO2(SPh)]
exhibited a broad EPR signal (g,
1.92; W
1/2, 20 G) characteristic of a
cis-[MoVO2]+
complex. The signal was stable when L = Lc but when
L = La
or Lb it was replaced by a proton-coupled signal
characteristic of a
cis-[MoVO(OH)]2+ center.
The complex LaMoVO(OH)(SPh) was isolated as a coprecipitate with
its conjugate base salt
[CoCp2][LaMoVO2(SPh)].
It was
characterized by infrared bands at 915 and 535
cm-1, assigned to ν(MoO) and
ν(MoOH) modes, respectively.
The anions were readily converted to air-stable
LMoVO(OSiMe3)(SPh) upon reaction with
Me3SiCl and reacted
with dioxygen to regenerate LMoVIO2(SPh).
The paper reports the first isolation in substance of compounds
containing
novel cis-[MoVO2]+
and cis-[MoVO(OH)]2+
centers and the first crystallographic characterization of a
cis-dioxo-Mo(V) species.