A Mixed-Valence Tri-Zinc Complex, [LZnZnZnL] (L=Bulky Amide), Bearing a Linear Chain of Two-Coordinate Zinc Atoms

Reduction of a variety of extremely bulky amido Group12 metal halide complexes, [LMX(THF)_0,1] (L=amide; M=Zn, Cd, or Hg; X=halide) with a magnesium(I) dimer gave a homologous series of two-coordinate metal(I) dimers, [L′MML′] (L′=N(Ar^†)(SiMe₃), Ar^†=C₆H₂{C(H)Ph₂}₂Prⁱ-2,6,4); and the formally zinc(0) complex, [L∗ZnMg(^MesNacnac)] (L∗=N(Arz.ast;)(SiPrⁱ₃); Arz.ast;=C₆H₂{C(H)Ph₂}₂Me-2,6,4; ^MesNacnac=[(MesNCMe)₂CH]^-, Mes=mesityl), which contains the first unsupported Zn-Mg bond. Two equivalents of [Lz.ast;ZnMg(^MesNacnac)] react with ZnBr₂ or ZnBr₂(tmeda) to give the mixed valence, two-coordinate, linear tri-zinc complex, [Lz.ast;Zn^IZn⁰Zn^ILv], and the first zinc(I) halide complex, [Lz.ast;ZnZnBr(tmeda)], respectively. The analogues [Lz.ast;ZnMZnLz.ast;] (M=Cd or Hg), were also prepared, the Cd species contains the first Zn-Cd bond in a molecular compound. Metal-metal bonding was studied by DFT calculations. Form an orderly queue! Reduction of an extremely bulky amido (Lz.ast;) zinc bromide complex, [Lz.ast;ZnBr] with a magnesium(I) dimer yields the formally zinc(0) complex, [Lz.ast;ZnMg(^MesNacnac)], which contains the first example of an unsupported Zn-Mg bond. Its subsequent reaction with ZnBr₂ affords the unprecedented mixed-valence, linear tri-zinc complex, [Lz.ast;Zn^IZn⁰Zn^ILz.ast;] (see picture).