Microsolvation and sp²-stereoinversion of monomeric α-(2,6-di-tert-butylphenyl)vinyllithium as measured by NMR

• Rudolf Knorr,
• Monika Knittl and
• Eva C. Rossmann

Beilstein J. Org. Chem. 2014, 10, 2521–2530, doi:10.3762/bjoc.10.263

• exclusively disolvated monomers in tert-butyl methyl ether, Et2O, TMEDA, or toluene with TMEDA (1.4 equiv). This was established at low temperatures through the observation of separated NMR signals for free and lithium-coordinated ligands and/or through the patterns and magnitudes of 13C,6Li NMR coupling

• with the transient immobilization of one additional THF ligand, followed by stereoinversion of the quasi-sp2-hybridized carbanionic center in cooperation with a “conducted tour” migration of Li+(THF)4 along the α-aryl group within the solvent-separated ion pair. Keywords: 13C,6Li NMR coupling; ion

• , t-BuOMe, and 1,2-bis(dimethylamino)ethane (TMEDA). All dimeric species of 1a and 1b are disolvated (d = 1 at each Li) by the above three donor ligands in toluene solution and in the solid state [9]. These d values were found [9] to change inversely with the magnitude of the scalar one-bond 13C,6Li