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)

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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.

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