Multinuclear NMR study of the solution structure and reactivity of tris(trimethylsilyl)methyllithium and its iodine ate complex.

The extreme steric bulk of tris(trimethylsilyl)methyl derivatives (1-X) provides interesting structural and dynamic behavior for study. Dynamic NMR studies on 1-SePh and 1-I showed restricted rotation around the C-Si bonds of each trimethylsilyl groups. An extensive multinuclear NMR study of natural abundance and (6)Li and (13)C enriched 1-Li revealed three species in THF-containing solvents, a dimer 1T, and two monomers, the contact ion pair 1C, and solvent separated ion pair 1S.

Reactivity of the triple ion and separated ion pair of tris(trimethylsilyl)methyllithium with aldehydes: a RINMR study.

Low-temperature rapid-injection NMR (RINMR) experiments were performed on tris(trimethylsilyl)methyllithium. In THF/Me2O solutions, the separated ion (1S) reacted faster than can be measured at -130 degrees C with MeI and substituted benzaldehydes (k >/= 2 s -1), whereas the contact ion (1C) dissociated to 1S before reacting. Unexpectedly, the triple ion reacted faster with electron-rich benzaldehydes relative to electron-deficient ones.

Interconversion of contact and separated ion pairs in silyl- and arylthio-substituted alkyllithium reagents.

Ether-solvated contact and separated ion pairs (CIP and SIP) for two lithium reagents, tris(trimethylsilyl)methyllithium (1) and bis(3,5-bistrifluoromethylphenylthio)methyllithium (2), have been characterized and observed for the first time under conditions of slow exchange by NMR spectroscopy, and barriers to interconversion have been measured. A Saunders isotope perturbation experiment was used to support identification of the CIP and SIP species for 2.