Reactions of LiCHR2 and related lithium alkyls with α-H free nitriles and the crystal structures of eleven representative lithium 1,3-diazaallyls, 1-azaallyls and β-diketiminates

Abstract

Reactions between bis(trimethylsilyl)methyllithium LiCHR₂ and a nitrile R′CN gave lithium 1-azaallyls, β-diketiminates or 1,3-diazaallyls. The products of related processes involving the lithium alkyl LiCH₂R, LiCH(R)Ph or [Li(tmen)]₂[1,2-{C(H)R}₂C₆H₄] have also been obtained (R = SiMe₃ and R′ = Bu^t, Ph or C₆H₄Me-4). Analytical and spectroscopic data served to identify the following crystalline compounds: [Li{N(R)C(Bu^t)C(H)R}(D)]_n [D absent and n = 2; D = tmen or dme and n = 1], [Li{N(R)C(Ph)C(H)R}(D)]_n [D = tmen or pmdien and n = 1, or D = thf and n = 2], [Li{N(R)C(Ph)C(H)C(R′′)NR}(D)]_n [D absent, n = 2 and R′′ = Ph (4a), C₆H₄Me-4 (4b) or Bu^t; or D = tmen, (thf)₂ (9b), NEt₃ or thf and NCPh and n = 1 and R′′ = Ph], [Li{N(R)C(Ph)C(H)C(Ph)NR}(D)Li(CHR₂)] [D = OEt₂ or thf], [Li{N(R)C(Ar)NC(Ph)C(H)R}(D)]_n [D = tmen, n = 1 and Ar = Ph or C₆H₄Me-4; or D = thf, n = 2 and Ar = Ph], [Li{N(Ph)C(R)NC(Ph)C(H)R}(tmen)], [Li{N(R)C(Bu^t)CH₂]₂, [Li{N(R)C(Ph)C(H)Ph}(tmen)], and [Li(tmen)]₂[1,2-{N(R)C(Bu^t)CH}₂C₆H₄]. Each of the three classes of ligands has a diversity of ligating possibilities, functioning towards lithium variously in a terminal or bridging and mono- or bi-dentate fashion, the role of a neutral donor D often being crucial. For an isomeric pair, the lithium β-diketiminate was thermodynamically preferred over the 1,3-diazaallyl. From [Li{N(R)C(Bu^t)C(H)R}]₂ and successively CH₂Br₂ and LiBuⁿ, the further lithium 1-azaallyl compound [Li{N(R)C(Bu^t)C(H)C(H)(R)Buⁿ}]₂ was obtained. From 4a and CH₂Br₂ or (BrCH₂)₂ a bis(β-diketiminyl)methane CH₂[C{C(Ph)NR}C(Ph)N(H)R]₂ or 9b or β-diketimine HN(R)C(Ph)C(H)C(Ph)NR were obtained, while 4b with successively KOBu^t and H₂O gave the β-diketimine HN(R)C(C₆H₄Me-4)C(H)C(C₆H₄Me-4)NR. Mechanistic pathways are proposed, which involve Me₃Si migrations: from C to N or N to N; or, for the latter a 1,2-dyotropic Me₃Si/H exchange. The crystal structures of eleven of these compounds have been determined. Each of the new lithium compounds may in principle behave as an N-, C-, (N,N′)-, or (N,C)-centred nucleophile. Reactions demonstrating the first two alternatives for the β-diketiminate [Li{N(R)C(Ar)C(H)C(Ar)NR}]₂ are (i) those with water (Ar = C₆H₄Me-4) or (BrCH₂)₂ (Ar = Ph) which gave the diketimine N(R)C(Ar)C(H)C(Ar)N(H)R, whereas (ii) that with CH₂Br₂ (Ar = Ph) yielded CH₂[C{C(Ph)NR}C(Ph)N(H)R]₂.