Oxotungsten(VI) Chemistry of Hydrotris(3,5-dimethylpyrazol-1-yl)borate: Hydroxodioxotungsten(VI), Trioxotungsten(VI), and (μ-Oxo)bis[dioxotungsten(VI)] Complexes

Colorless, diamagnetic, air-stable
LWVIO2(OH) [L =
hydrotris(3,5-dimethylpyrazol-1-yl)borate] forms
when
suspensions of LWIII(CO)3 in dimethyl
sulfoxide are heated at 100 °C. The complex was characterized
by
microanalysis, high-resolution mass spectrometry, and IR, NMR, and
EXAFS spectroscopic techniques. The
complex behaves as a weak acid with a pKa of
around 4.7. Reaction of LWO2(OH) with
NEt4OMe results in the
formation of colorless, diamagnetic, air-stable
NEt4[LWVIO3], which
crystallizes as a tetrahydrate. Crystals of
NEt4[LWO3]·4H2O are
monoclinic, space group P21/c, with
a = 18.804(4) Å, b = 9.901(8) Å,
c = 17.447(3) Å,
β = 104.35(2)°, and V = 3146(1)
Å3 for Z = 4. The structure is composed
of discrete NEt4+ and
fac-[LWO3]-
ions strung in an alternating fashion along both sides of a zigzag
ladder of hydrogen-bonded water molecules
(directed parallel to the b axis). The
distorted-octahedral [LWO3]- anions, with
W−O(1) = 1.740(4) Å, W−O(2)
= 1.759(4) Å, and W−O(3) = 1.765(4) Å, are
hydrogen-bonded to water molecules through two oxo groups,
with WO(2)··O(5)i = 2.666(6) Å and
WO(3)··O(4)ii = 2.693(6) Å. The
EXAFS spectra of
NEt4[LWO3]·4H2O
and LWO2(OH) and related complexes are diagnostic of
the respective trioxo or hydroxo−dioxo centers present.
Colorless, diamagnetic, air-stable
[LWVIO2]2(μ-O) is produced
in a number of reactions, including the oxidation
of LWVIO2(μ-O)WIVO(CO)L and
metathesis reactions involving LWVIO2Cl.
The complex exhibits NMR spectra
consistent with molecular C2 symmetry and IR
bands assignable to ν(WO2) (945 and 900
cm-1) and
νas(WOW)
(780 cm-1) vibrational modes. Crystals
of [LWVIO2]2(μ-O) are
monoclinic, space group C2/c, with a
= 28.112(7) Å, b = 9.538(7) Å, c =
15.722(8) Å, β = 115.56(2)°, and V =
3802(3) Å3 for Z = 4. The dinuclear
structure
is composed of distorted-octahedral LWO2 units linked by
the μ-oxo ligand; the terminal WO bond lengths are
identical at 1.715(5) Å, while the bridging W−O(3) distance is
1.893(1) Å.