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.