Solution characterizations and ligand binding constants were determined for n-butyllithium in hydrocarbon and ethereal solvents using diffusion-ordered NMR. In hydrocarbon solvents, n-butyllithium exists primarily as an octamer at -40 °C and deaggregates to a hexamer when the temperature is increased. In the presence of THF or diethyl ether, n-butyllithium exists predominantly as a tetra-solvated tetramer and deaggregates to a tetra-solvated dimer in the presence of a large excess or neat THF. The ligand binding constants for the tetra-solvated tetramers were measured using H NMR/DOSY titration.

We report the direct measurement of ligand-binding constants of organolithium complexes using a H NMR/diffusion-ordered NMR spectroscopy (DOSY) titration technique. Lithium hexamethyldisilazide complexes with ethereal and ester donor ligands (THF, diethyl ether, MTBE, THP, tert-butyl acetate) are characterized usingH NMR and X-ray crystallography. Their aggregation and solvation states are confirmed using diffusion coefficient-formula weight correlation analysis, and the H NMR/DOSY titration technique is applied to obtain their binding constants. Our work suggests that steric hindrance of ethereal ligands plays an important role in the aggregation, solvation, and reactivity of these complexes. It is noteworthy that diffusion methodology is utilized to obtain binding constants.

A straightforward procedure is outlined for prediction of the complete three-dimensional coordinate set for a highly disordered phase. For a mother and daughter phase, where one of the pair has an “unsolvable” structure, one needs only to (a) establish the topotaxy using previously published techniques, (b) obtain the topotactic transformation matrix, φ, between the ordered and highly disordered phase, and (c) apply the transpose of φ–1 to obtain a trial set of coordinates for refinement using the reflection data set of the highly disordered phase. For the inclusion compound [Fe­(η-C5H5)]­·3­(NH2)2CS (1), which contains highly disordered ferrocene molecules above 160 K (polymorph 1_I), we found a more ordered structure at low temperature. At 135 K (polymorph 1_II), two ferrocene moieties are present in the thiourea channel in an approximately 1:1 ratio. One is nearly orthogonal (87.0°) to the channel axis, while the other is tipped 16.2° from that direction. Using steps (a–c) outlined above, a trial structure may be obtained for 1_I, and refinement leads to R 1 = 4.25%. The structure of 1_1, containing 12-fold disordered ferrocene molecules, is similar to that found at temperatures below the phase transition, with a greater amount of the orthogonal orientation (55:45 vs 51:48), consistent with, but lower than, amounts found using solid-state NMR techniques. The low temperature polymorph is a trill, with an approximately 3:1:1 ratio of twin components. The exact alignment of the mother phase and the three daughters has been established using the methods of topotactic analysis described previously.