Subvalent group 4B metal alkyls and amides. Part 7. Transition-metal chemistry of metal(II) bis(trimethylsilyl)amides M′(NR2)2(R = SiMe3; M′= Ge, Sn, or Pb)

Abstract

The transition-metal (M) chemistry of the compounds M′(NR₂)₂(M′= Ge, Sn, or Pb; R = SiMe₃) falls into three categories. These heavy Group 4B atom carbene analogues behave as (a) M′-centred neutral ligands with respect to Lewis acids, (b) co-ordinatively unsaturated fragments, by inserting into transition-metal M–X bonds, or (c) as sources of other bivalent molecules M′X′₂. Reactions of class (a) afford complexes in which the Group 4 metal atom is usually [but note: [W(CO)₅{SnCl(NR₂)(thf)}](thf = tetrahydrofuran) in a three-co-ordinate environment, as in [M(CO)₅{M′(NR₂)₂}](M = Cr, Mo, or W; M′= Ge or Sn), trans-[M(CO)₄{M′(NR₂)₂}₂](M = Mo or W, M′= Ge or Sn), [Sc(η-C₅H₅)₂-Me{Sn(NR₂)₂}], or cis-[Pd(η-C₃H₅)Cl{M′(NR₂)₂}](M′= Sn or Pb). Reactions of class (b) afford complexes in which the Group 4 metal atom is in a four-co-ordinated environment, as in [Mn(CO)₅-{SnBr(NR₂)₂}], [Fe(η-C₅H₅)(CO)₂{Sn(NR₂)₂X}](X = F, I, or Me), [{Pt(µ-Cl)[M′Cl(NR₂)₂](PEt₃)}₂](M′= Ge, Sn, or Pb), or cis-[Pd(cod){SnCl(NR₂)₂}₂](cod = cyclo-octa-1,5-diene). A product of a reaction of type (c) is [Sn{Mo(η-C₅H₅)(CO)₃}₂]. Type (a) reactions are those in which an M′(NR₂)₂ ligand either displaces another neutral ligand (CO or olefin) from the inner co-ordination sphere of a transition metal, or effects the nucleophilic cleavage of an M(µ-Cl)₂M bridge. Type (b) reactions are insertions of an M′(NR₂)₂ moiety into a transition metal–halide or –alkyl bond, while the sole type (c) reaction demonstrates the facility with which the N(SiMe₃)₂^– group is displaced from the Group 4 metal M′ by a transition metal-centred nucleophile.