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

(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 (H-1, C-13, Li-7). 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 [Li-2(CH2NPh2)(2)(THF)(3)] (1c') and [Li-4(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) Angstrom) 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) Angstrom) and by the oxygen atom of the disordered THF molecule. 1d' is a tetrameric species exhibiting a molecular C-2 symmetry. The lithium atoms are arranged in a distorted tetrahedron with methylene carbon atoms occupying each face of the tetrahedron. (C) 1997 Elsevier Science S.A.