Method of continuous variation: characterization of alkali metal enolates using ¹H and ¹⁹F NMR spectroscopies

The method of continuous variation in conjunction with (1)H and (19)F NMR spectroscopies was used to characterize lithium and sodium enolates solvated by N,N,N',N'-tetramethylethyldiamine (TMEDA) and tetrahydrofuran (THF). A strategy developed using lithium enolates was then applied to the more challenging sodium enolates. A number of sodium enolates solvated by TMEDA or THF afford exclusively tetramers. Evidence suggests that TMEDA chelates sodium on cubic tetramers.

Lithium phenolates with a hexagonal-prismatic Li6O6 core isolated via a cage-shaped tripodal ligands system: crystal structures and their behavior in solution

Stable hexanuclear lithium phenolate bearing a cage-shaped tripodal ligand was isolated, which had a hexagonal-prismatic Li(6)O(6) core at room temperature, because of the hard mobility of the ligand and its reduction of the problematic steric repulsion. The properties of the lithium phenolates were analyzed by X-ray crystallography and NMR spectroscopy.

Analogy of the Coordination Chemistry of Alkaline Earth Metal and Lanthanide Ln2+ Ions: The Isostructural Zoo of Mixed Metal Cages [IM(OtBu)4{Li(thf)}4(OH)] (M=Ca, Sr, Ba, Eu), [MM′6(OPh)8(thf)6] (M=Ca, Sr, Ba, Sm, Eu, M′=Li, Na), and their Derivatives with 1,2-Dimethoxyethane

As previously shown, alkali and alkaline earth metal iodides in nonaqueous, aprotic solvents behave like transition metal halides, forming cis- and trans-dihalides with various neutral O-donor ligands. These compounds can be used as precursors for the synthesis of new mixed alkali/alkaline earth metal aggregates. We show here that Ln2+ ions form isostructural cluster compounds. Thus, with LiOtBu, 50% of the initial iodide can be replaced in MI2, M=Ca, Sr, Ba, Eu, to generate the mixed-metal alkoxide aggregates [IM(OtBu)4{Li(thf)}4(OH)], for which the M--OH contacts were investigated by theoretical methods. With M'OPh (M'=Li, Na), a new mixed-metal aryloxide cluster type [MM'6(OPh)8(thf)6] is obtained for M=Ca, Sr, Ba, Sm, Eu. Their stability versus DME (DME=1,2-dimethoxyethane) as bidentate ligand is studied.

4-Methoxy- and 4-cyano-substituted lithium aryloxides: electronic effects of substituents on aggregation

The para-substituted lithium aryloxides [{4-NC-C6H4OLi.(Pyr)2}2.Pyr] 1a, [{4-NC-C6H4OLi.(THF)2}2] 1b, [{4-MeO-C6H4OLi.Pyr}4] 2a, [4-MeO-C6H4OLi.(THF)n] 2b, [{4-NC-2,6-(t-Bu)2-C6H2OLi.(Pyr)2}infinity] 3a, [{4-NC-2,6-(t-Bu)2-C6H2OLi.(THF)2}infinity] 3b, [{4-MeO-2,6-(t-Bu)2-C6H2OLi.Pyr}2.(Pyr)2] 4a, and [4-MeO-2,6-(t-Bu)2-C6H2OLi.(THF)n] 4b were prepared by the direct deprotonation of the corresponding phenol with an alkyllithium base (BuLi or MeLi) in the appropriate solvent, either pyridine or THF. All compounds were characterized by 1H and 13C NMR spectroscopy, and the crystal structures of 1a, 1b, 2a, 3a, 3b and 4a were elucidated. The cyano derivatives 1a and 1b adopt discrete tetrasolvated Li2O2 ring dimers whereas the methoxy analogue 2a crystallizes as a tetrasolvated molecular tetramer with a pseudo cubic Li4O4 core. The sterically encumbered cyano derivatives 3a and 3b form isostructural 1D polymeric chains of monomers via bridging of the phenolate ligands through Li...NC and Li-O contacts. In comparison, the crystal structure of the methoxy counterpart 4a is a disolvated molecular Li2O2 ring dimer. Solution NMR spectroscopic studies of 1-4 in d5-pyridine and d8-THF indicate that the methoxy complexes are more highly aggregated than the cyano derivatives, consistent with the solid-state studies. Ab initio molecular orbital calculations at the HF/6-31G* level of theory indicate that the origin of the aggregation state variations between the cyano and methoxy complexes is due to electronic effects.

Synthesis of group 1 metal 2,6-diphenylphenoxide complexes [M(OC6H3Ph2-2,6)] (M = Li, Na, K, Rb, Cs) and structures of the solvent-free complexes [Rb(OC6H3Ph2-2,6)]x and [Cs(OC6H3Ph2-2,6)x: one-dimensional extended arrays of metal aryloxides

Reaction of 2,6-diphenylphenol (HOC(6)H(3)Ph(2)-2,6) with (n)BuLi, NaH, KH, or Rb or Cs metal in benzene gives the solvent-free complexes [M(OAr)]x in excellent yield. The complex [Rb(OC(6)H(3)Ph(2)-2,6)](x)() exhibits a ladderlike structure in the solid state with triply bridging oxygen atoms and Rb-O distances of 2.743(3), 2.930(2), and 2.973(2) A. The Rb cations interact with the pi-electron cloud of the arene moieties, giving rise to a high Rb coordination number. The cesium-containing congener forms a layered, columnlike structure consisting of [Cs(2)(mu(2)-OAr)(2)] units, with nearly identical Cs-O distances of 2.945(2) and 2.947(2) A. The individual layers are held together solely by Cs-arene pi-interactions.

Powder Structure Solutions of the Compounds Potassium Phenoxide-Phenol: C(6)H(5)OK.xC(6)H(5)OH (x = 2, 3)

We report the ab initio structure solutions of two solvent containing potassium phenoxides by high-resolution powder X-ray diffraction. Both compounds are of interest for the classification of the mechanism of Kolbe-Schmitt type reactions. C(6)H(5)OK.2C(6)H(5)OH crystallizes in space group Abm2, Z = 4, with unit cell parameters a = 10.12458(4) Å, b = 21.2413(1) Å, c = 7.89784(3) Å. C(6)H(5)OK.3C(6)H(5)OH crystallizes in space group Pbca, Z = 8, with unit cell parameters a = 22.7713(1) Å, b = 25.4479(2) Å, c = 7.75549(4) Å. Both compounds show polymeric zigzag chains [K([6])O(2)([2])O([1])pi(phenyl)([1])] aligned along the c-axis. The coordination of the potassium ions is similar for both compounds. They lie at the center of distorted octahedra of five oxygen atoms and one phenyl ring, which donates its pi electrons. The distortion decreases as the number of free phenol increases.