Synthesis and characterization of substituted (aminomethyl)lithium compounds: The structures of [Li2(CH2NPh2)2(THF)3] and [Li4(CH2NC5H10)4(THF)2]

Article abstract of DOI:10.1016/S0022-328X(97)00404-X

(Aminomethyl)lithium compounds LiCH₂NRR′ · x THF (NRR′ = NMe₂ (1a, x = 0), NPhMe (1b, x = 2), NPh₂ (1c, x = 1 ... 1,5), NC₅H₁₀ (1d, x = 0, NC₅H₁₀ = piperidino), and NC₇H₁₄ (1e, NC₇H₁₄ = 2,6-dimethylpiperidino)) were prepared by the reaction of Bu₃SnCH₂NRR′ with BuLi. 1a-d were isolated in solid state and characterized by NMR spectroscopy (¹H, ¹³C, ⁷Li). 1e was obtained in solution and characterized via reaction with MeOH and with benzophenone to generate MeNC₇H₁₄ and Ph₂C(OH)CH₂NC₇H₁₄, respectively. Recrystallization of 1c and 1d from n-hexane/THF gives [Li₂(CH₂NPh₂)₂(THF)₃] (1c′) and [Li₄(CH₂NC₅H₁₀)₄(THF)₂] (1d′), respectively, whose structures (X-ray) were determined. The dimeric compound 1c′ forms a central planar four-membered Li₂C₂ ring. One lithium atom is four-coordinated to two methylene carbon atoms (d(Li-C) = 2.246(9), 2.235(9) A) and two oxygen atoms of THF. Unusually, the second lithium exhibits a nearly planar coordination sphere represented by two methylene carbon atoms (d(Li-C) = 2.17(1) and 2.16(1) A) and by the oxygen atom of the disordered THF molecule. 1d′ is a tetrameric species exhibiting a molecular C₂ symmetry. The lithium atoms are arranged in a distorted tetrahedron with methylene carbon atoms occupying each face of the tetrahedron.