Intramolecular penta- and hexacoordinate tetraorganotin compounds containing the 8-(dimethylamino)-1-naphthyl ligand

Article abstract of DOI:10.1021/om00050a025

A series of novel tetraorganotin compounds, Sn[(8-Me₂N)C₁₀H₆-1]RR′R″, containing the 8-(dimethylamino)-1-naphthyl group, has been synthesized and characterized. For one of these compounds (R = R′ = R″ = Ph) the molecular structure in the solid state has been determined by X-ray diffraction methods: C₃₀H₂₇NSn, monoclinic, space group P2₁/a, and a = 24.8365 (7) ?, b = 12.3785 (4) ?, c = 17.1997 (6) ?, β = 109.102 (3)°, and Z = 8; final R = 0.031 for 7920 observed reflections. The tin center has a distorted trigonal-bipyramidal coordination geometry with the nitrogen atom (Sn-N = 2.884 (3) ?) and one of the phenyl groups at approximately axial positions. The structure of this tetraorganotin compound was compared with that of [8-(dimethylamino)-1-naphthyl]methylphenyltin bromide, for which the structure in the solid state has been determined by X-ray diffraction methods: C₁₉H₂₀BrNSn, monoclinic, space group P2₁/a, with a = 16.356 (3) ?, b = 13.922 (4) ?, c = 8.082 (2) ?, β = 102.91 (2); and Z = 4; final R = 0.042 for 2804 observed reflections. The tin center has a trigonal-bipyramidal coordination geometry in which the organic ligands occupy the equatorial sites, while the more electronegative Br and N ligands are in the axial positions. ¹H, ¹³C, and ¹¹⁹Sn NMR spectra of the tetraorganotin compounds show that, most likely as a result of the fixed orientation of the nitrogen atom with respect to the tin atom, also in solution these species are pentacoordinate. This may be concluded from the observations that (i) the ¹H and ¹³C NMR spectra of chiral [8-(dimethylamino)-1-naphthyl]methylphenylneopentyltin show two resonances for the diastereotopic NMe₂ group, indicating that pyramidal inversion of the nitrogen atom is blocked, and (ii) the increase of the ¹J(¹¹⁹Sn-¹³C(1)_naphthyl) values compared to those of unsubstituted naphthyltin compounds points to a coordination number larger than 4. Moreover, the tetraorganotin compounds show an enhanced reactivity in redistribution reactions, which may be the result of the labilization of the Sn-C bond in a trans position with respect to the coordinating nitrogen atom.