SOLVATION OF AGGREGATES OF LITHIUM PHENOLATES BY HEXAMETHYLPHOSPHORIC TRIAMIDE - HMPA CAUSES BOTH AGGREGATION AND DEAGGREGATION

The tetramer of lithium 3,5-dimethylphenolate in diethyl ether undergoes sequential solvation by HMPA and is fully converted to the HMPA tetrasolvate by 1 equiv of the cosolvent. Addition of 8 equiv of HMPA does not cause dissociation of the tetramer. Addition of HMPA to lithium p-bromo- and p-(trifluoromethyl)phenolates in THF results in conversion of their dimers to tetramers and, at high cosolvent ratios, monomers. Two equivalents of HMPA in either THF or diethyl ether converts dimeric lithium 2,6-dimethylphenolate to the monomer. C-13, Li-7, and P-31 chemical shifts for the various HMPA solvates are reported. The Li-7 quadrupole splitting constant for tetrameric lithium 3,5-dimethylphenolate HMPA tetrasolvate is 35 kHz. Lithium p-bromophenolate in THF at -120-degrees-C forms a small quantity of a trimer together with the dimer and tetramer.