Extremely bulky amido-group 14 element chloride complexes: Potential synthons for low oxidation state main group chemistry

Abstract

The preparation of a series of extremely bulky secondary amines, Ar*N(H)SiR₃ (Ar* = C₆H₂{C(H)Ph₂}₂Me-2,6,4; R₃ = Me₃, MePh₂ or Ph₃) is described. Their deprotonation with either LiBuⁿ, NaH or KH yields alkali metal amide complexes, several monomeric examples of which, [Li(L){N(SiMe₃)(Ar*)}] (L = OEt₂ or THF), [Na(THF)₃{N(SiMe₃)(Ar*)}] and [K(OEt₂){N(SiPh₃)(Ar*)], have been crystallographically characterised. Reactions of the lithium amides with germanium, tin or lead dichloride have yielded the first structurally characterised two-coordinate, monomeric amido germanium(II) and tin(II) chloride complexes, [{(SiR₃)(Ar*)N}ECl] (E = Ge or Sn; R = Me or Ph), and a chloride bridged amido-lead(II) dimer, [{[(SiMe₃)(Ar*)N]Pb(μ-Cl)}₂]. DFT calculations on [{(SiMe₃)(Ar*)N}GeCl] show its HOMO to exhibit Ge lone pair character and its LUMO to encompass its Ge based p-orbital. A series of bulky amido silicon(IV) chloride complexes have also been prepared and several examples, [{(SiR₃)(Ar*)N}SiCl₃] (R₃ = Me₃, MePh₂) and [{(SiMe₃)(Ar*)N}SiHCl₂], were crystallographically characterised. The sterically hindered group 14 complexes reported in this study hold significant potential as precursors for kinetically stabilised low oxidation state and/or low coordination number group 14 complexes.