Synthesis, Structures, and Kinetics of Mixed-Donor Amido−Amino−Siloxo Ligands from Symmetrical Diamidosilyl Ether Ligands via a Retro-Brook Rearrangement

Deprotonation of the new (R = propyl, 3,5-Me2Ph) and previously prepared (R = 2,4,6-Me3Ph, 2,6-iPr2Ph, 3,5-(CF3)2Ph) symmetrical diamidosilyl ether ligand precursors {[RNHSiMe2]2O} with 2 equiv of nBuLi in THF resulted
in a new class of mixed-donor amido−amino−siloxo ligands of the form {RNLiSiMe2N(R)SiMe2OLi} (R= propyl
(1c), 3,5-Me2Ph (2c), 2,4,6-Me3Ph (3c), 2,6-iPr2Ph (4c), 3,5-(CF3)2Ph (5c)) in one-step and high yield via a retro-Brook-type rearrangement mechanism. Ligands 1c, 3c, and 4c have been structurally characterized in the presence
and absence of THF/ether donor solvents and exhibited a range of aggregated structures with ring-laddering,
ring-stacking, and cubane motifs; higher-nuclearity clusters for base-free systems were observed for 1c and 4c.
1H, 7Li, and selected 13C{1H} NMR spectra in THF-d8 and toluene-d8 are described; the 7Li data are indicative of
intramolecular fluxional behavior as a function of temperature but do not shed light on the nuclearity of the salts
in solution. Reaction kinetics were investigated by variable-temperature 1H NMR spectroscopy and showed that
the rate of rearrangement reactions increases with decreasing steric hindrance and with increasing electron-donating
ability of the R substituents, with τ1/2 values ranging from 5.7 × 101 to 1.5 × 108 s for 2c and 5c, respectively.