Oxide Formation upon Thermolysis of a Pb(II)/Zr(IV) Alkoxide

While
Pb(μ-OtBu)3Zr(OtBu)3
is stable for days in refluxing toluene, addition of stoichiometric
[Pb(OtBu)2]3
prior to reflux yields tBuOH,
H2CCMe2, and
Pb3ZrO(OtBu)8, which
was characterized by multinuclear NMR and
X-ray diffraction. Highly pure
[Pb(OtBu)2]3 itself is
unchanged in refluxing toluene, although it is slowly
converted
to Pb4O(OtBu)6 by catalytic
quantities of tBuOH, LiNMe2, or
HN(SiMe3)2, but not by Pb metal.
Stoichiometric
water converts [Pb(OtBu)2]3
completely to Pb4O(OtBu)6,
which reacts at 25 °C with
Zr(OtBu)4 to give
Pb3ZrO(OtBu)8. Since
PbZr(OtBu)6 and
[Pb(OtBu)2]3 show no
NMR spectroscopic evidence of reacting at 25 °C in
toluene,
the mechanism of the formation of
Pb3ZrO(OtBu)8 is
suggested to involve O/C heterolysis and C−H bond
scission
as the rate determining step during thermolysis. Convenient
syntheses of Pb4O(OtBu)6 and
Pb6O4(OtBu)4 are
described,
and 207Pb and 17O NMR spectra of all
species are described. Crystallographic data for
Pb3ZrO(OtBu)8 (at
−174 °C)
include a = 16.663(2) Å, b =
12.608(1), c = 21.117(2), and Z = 4
in space group Pbc21.