Nucleophilic attack within Ge, Sn and Pb complexes containing Me2N(CH2)3 - As a potential intramolecular donor ligand

Article abstract of DOI:10.1016/s0020-1693(98)00071-1

Thirteen tin compounds L_xPh_ySnCl_z and LPh₂SnPhX (x=1-4, y=0-3, z=0-2; X=Ph, F, Cl, Br, I, OPh), six germanium compounds L_xPh_yGeCl_z and four lead compounds LPh₂PbPhX (X=Ph, Cl, Br, I) containing the potential intramolecular donor L = Me₂N(CH₂)_3- have been synthesized by Grignard reactions, redistribution, halogenation, exchange of halide and phenylation. Evidence for 1,5-chelation in which the donor Me₂N intramolecularly attacks the Lewis-acidic atoms Ge, Sn or Pb is provided by six crystal structure determinations: Me₂N(CH₂)₃SnPh₂Cl,5;Me ₂N(CH₂)₃SnPh₂Br,5a;Me ₂N(CH₂)₃SnPh₂I,5b;Me ₂N(CH₂)₃SnPh₂OPh,5d;Me ₂N(CH₂)₃SnPh3·HCl·H₂O, 1a; Me₂N(CH₂)₃PbPh₂I, 17b), and by solution ¹³C, ¹¹⁹Sn and ²⁰⁷Pb NMR data. This nucleophilic attack originates from the π-basicity and the charge flow from the ligands into a σ*-LUMO at Ge, Sn or Pb. The electronegativity of the ligands at Ge, Sn or Pb inhibits nucleophilic attack. The ligand sequences PhCl₂>Ph₂Cl>PhCl>Ph₃ and Ph₂I>Ph₂Br>Ph₂OPh>Ph ₂Cl>Ph₂F hold for an increasing approach (N?Ge/Sn/Pb). The δ values (¹³C) of the α-methylene in CDCl₃ solution are shifted distinctly to high frequency by increasing the approach between the Me₂N donor and the central atom. A qualitative discussion of ¹¹⁹Sn NMR chemical shifts and spin-spin coupling constants is given, which supports the arguments on the basis of interactions of frontier orbitals.