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

Abstract

The synthesis and structure of lithium, magnesium, and zinc complexes N,N'-chelated by a hybrid amine-amido ligand ([2-(Me₂NCH₂)C₆H₄NR]^-, abbreviated as L^NR, where R = H, SiMe₃, or Bn) are reported. The reaction of the least sterically demanding L^NH with various magnesium sources gives the hexameric imide [L^NMg]₆ (4) by the elimination of n-butane from L^NHMgⁿBu (2) or by the reaction of L^NHLi (1) with MeMgBr. [L^NH]₂Mg (3) is obtained through the addition of 0.5 equiv of ⁿBu₂Mg or Mg[N(SiMe₃)₂]₂ to L^NH₂ and with 1 equiv of ⁿBu₂Mg reacting to 2. Both L^NHMgN(SiMe₃)₂ (6) and isostructural L^NHZnN(SiMe₃)₂ (16) have been prepared using two different approaches: monodeprotonation of L^NH₂ by Zn/Mg[N(SiMe₃)₂]₂ in a 1:1 ratio or ligand substitution of 2 or L^NHZnEt (12) by 0.5 equiv of Sn[N(SiMe₃)₂]₂. The reactions of 2 or 3 with 1 provide the heterotrimetallic complex [L^NH]₄Li₂Mg (5). Benzyl- or trimethylsilyl-substituted anilines [L^N(SiMe₃)H (7) and L^N(Bn)H (8)] with 0.5 equiv of ⁿBu₂Mg allow the formation of homoleptic bis(amides) of the [L^N(R)]₂Mg type (10 and 11). Nevertheless, only the silylated secondary amine 7 is able to provide the heteroleptic n-butylmagnesium amide L^N(SiMe₃)MgⁿBu (9) upon reaction with an equimolar amount of ⁿBu₂Mg. Similarly, 12, [L^NH]₂Zn (13), L^N(R)ZnEt (17 and 18), and [L^N(R)]₂Zn [R = SiMe₃ (19) and Bn (20)] were prepared by the monodeprotonation of L^NH₂ or L^N(R)H using Et₂Zn in the corresponding stoichiometric ratio. L^NHZnI was prepared by the nucleophilic substitution of an ethyl chain in 12 by molecular iodine. A heterometallic complex, [L^NH]₄Li₂Zn (14), analogous to 5 was prepared from 12 or 13 with 1 or 2 equiv of 1, respectively.