Isolation and Structural Characterization of Unsolvated Lithium Aryls

Karin Ruhlandt-Senge, Jeffrey J. Ellison, Rudolf J. Wehmschulte, Frank Pauer, Philip P. Power

Research output: Contribution to journalArticle

165 Scopus citations

Abstract

The synthesis and characterization of three examples of unsolvated lithium aryls are described. The compounds {Li(Trip)}4 (1, Trip = 2,4,6-i-Pr3C6H2), {Li(2,6-Mes2C6H3)}2 (2, Mes = 2,4,6-Me3C6H2), {Li(n-Bu)}2(LiMes*)2 (3), and {Li(n-Bu)}2(LiMes*)2·Mes*Br (3·Mes*Br, Mes* = 2,4,6-i-Bu3C6H2) were synthesized by a metal-halogen exchange reaction between n-butyllithium and the appropriate aryl bromide (1 and 3) or iodide (2). The X-ray crystal structures of 1 and 3 show that they are tetrametallic lithium species involving almost planar arrays of four lithium atoms. The bonding involves both σ- and π-interactions to the aryl ligands. In contrast, the structure of 2 is dimeric with the two aryl groups linked by two µ2-bridging lithiums which are primarily σ-bonded to ipso carbons. Weaker interactions were also observed between the ortho mesityl substituents and the lithiums. The structure of 3 Mes*Br shows that the halide starting material Mes*Br can be included in the isolated crystals. This is a consequence of the fact that the metal-halogen exchange reaction used in their synthesis is sluggish. The main reasons for this probably are the use of hydrocarbon rather than ether solvent and the large size of the aryl ligands. The compounds were characterized by 1H, 13C, and 7Li NMR spectroscopy and X-ray crystallography and represent the first examples of structurally characterized simple, nonsolvated, σ-bonded lithium aryls. Crystal data with Mo Kα (λ = 0.71069 Å) at 130 K: 1, a = b = 13.098(2) Å, c = 16.791(8) Å, V = 2881(2) Å3, Z = 2, space group, 597 (I > 2σ(I)) data, R = 0.089; 2, a = 30.190(7) Å, b = 13.423(2) Å, c = 19.048(4) Å, V = 7719(3) A3, Z = 8 (two independent molecules), space group Pnna, 3419 (I> 2σ(I)) data, R = 0.097; 3, a = 22.721(11) Å, b = 10.072(5) Å, c = 19.327(8) Å, V = 4423(3) A3, Z = 4, space group Pna21 1811 (I > 2.5σ(I)) data, R = 0.082; 3·Mes*Br, a = 11.385(2) Å, b = 15.261(3) Å, c = 17.458(5) Å, β = 91.16(2)°, V= 3032.4(12) Å3, Z = 2, space group C2/m, 1821 (I > 3σ(I)) data, R = 0.104.

Original languageEnglish (US)
Pages (from-to)11353-11357
Number of pages5
JournalJournal of the American Chemical Society
Volume115
Issue number24
DOIs
StatePublished - Dec 1 1993
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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