Lithium, Magnesium, and Zinc Centers N,N'-Chelated by an Amine-Amide Hybrid Ligand

The synthesis and structure of lithium, magnesium, and zinc complexes N,N'-chelated by a hybrid amine-amido ligand ([2-(Me₂NCH₂)C₆H₄NR]^-, abbreviated as LR, where R = H, SiMe₃, or Bn) are reported. The reaction of the least sterically demanding LH with various magnesium sources gives the hexameric imide [LMg]₆ (4) by the elimination of n-butane from LHMgBu (2) or by the reaction of LHLi (1) with MeMgBr. [LH]₂Mg (3) is obtained through the addition of 0.5 equiv of Bu₂Mg or Mg[N(SiMe₃)₂]₂ to LH₂ and with 1 equiv of Bu₂Mg reacting to 2. Both LHMgN(SiMe₃)₂ (6) and isostructural LHZnN(SiMe₃)₂ (16) have been prepared using two different approaches: monodeprotonation of LH₂ by Zn/Mg[N(SiMe₃)₂]₂ in a 1:1 ratio or ligand substitution of 2 or LHZnEt (12) by 0.5 equiv of Sn[N(SiMe₃)₂]₂. The reactions of 2 or 3 with 1 provide the heterotrimetallic complex [LH]₄Li₂Mg (5). Benzyl- or trimethylsilyl-substituted anilines [L(SiMe₃)H (7) and L(Bn)H (8)] with 0.5 equiv of Bu₂Mg allow the formation of homoleptic bis(amides) of the [L(R)]₂Mg type (10 and 11). Nevertheless, only the silylated secondary amine 7 is able to provide the heteroleptic n-butylmagnesium amide L(SiMe₃)MgBu (9) upon reaction with an equimolar amount of Bu₂Mg. Similarly, 12, [LH]₂Zn (13), L(R)ZnEt (17 and 18), and [L(R)]₂Zn [R = SiMe₃ (19) and Bn (20)] were prepared by the monodeprotonation of LH₂ or L(R)H using Et₂Zn in the corresponding stoichiometric ratio. LHZnI was prepared by the nucleophilic substitution of an ethyl chain in 12 by molecular iodine. A heterometallic complex, [LH]₄Li₂Zn (14), analogous to 5 was prepared from 12 or 13 with 1 or 2 equiv of 1, respectively.