Abstract
The recent measurement (J. Am. Chem. Soc.2008, 130, 14179–14188) of the microsolvation numbers of monodentate, nonchelating ethereal donor ligands coordinating to the monomers and dimers of two sterically shielded ═C(aryl)–Li compounds permits the determination of well-founded dimerization enthalpies (ΔH0) and entropies (ΔS0) from properly formulated equilibrium constants, which must include the concentrations of the free donor ligands. The monomers are found to dimerize endothermically (ΔH0 > 0) in [D8]toluene solution in the presence of the donor tBuOMe or THF, but only slightly exothermically (ΔH0 = −0.5 kcal per mol of dimer) with the donor Et2O. The dimerization entropies ΔS0 (in cal mol–1 K–1) with the respective equivalents of released donor ligands are 7.2 and 11.0 (with 2 equiv of tBuOMe in the two cases), 6.1 (with 2 Et2O), and 34.1 (with 4 THF). It is shown that the improper omission of microsolvation from the equilibrium constant (a usual practice when the ligand numbers are not known) can lea...
Published Version
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