Evidence for hexacoordinate tin centers in triorganotin halides containing two 8-(dimethylamino)-1-naphthyl ligands

A series of novel triorganotin halides, SnX[1-C₁₀H₆NMe₂-8]₂R, containing two potentially intramolecular-coordinating 8-(dimethylamino)-1-naphthyl groups has been synthesized and characterized. The compounds were prepared via oxidative addition of an alkyl halide RX (R = Me, X = I; R = Et, X = I; R = benzyl, X = Br) to bis[8-(dimethylamino)-1-naphthyl]tin(II). From one of these compounds (R = Me, X = I) the molecular structure in the solid state has been determined by X-ray diffraction methods: C₂₅H₂₇IN₂Sn, orthorhombic, space group Pbca with a = 19.212 (3) Å, b = 25.540 (8) Å, c = 9.482 (1) Å, and Z = 8, final R = 0.052 for 1798 observed reflections. The tin center has a distorted-octahedral coordination geometry with mutual trans positions of the two C(1)_naphthyl atoms, one of the coordinating nitrogen atoms and the iodine atom, and the other coordinating nitrogen atom and the methyl group at tin. The length of the Sn-N bond trans to the iodine atom is in the normal range as expected for a Sn-N coordination bond (2.53 (1) Å) while the Sn-N bond trans to the methyl group is extremely long (3.10 (1) Å). ¹H, ¹³C, and ¹¹⁹Sn NMR spectra of these triorganotin halides show that, at low temperature in solution, these compounds exist in two geometrically different forms, one as found in the solid state and one with the two C(1)_naphthyl atoms, the two coordinating nitrogen atoms, and the methyl group at tin and the iodine atom in cis position. At higher temperatures a process involving interconversion between these two isomers becomes fast on the NMR time scale.