Bis(halodiphenylstannyl)alkanes as bidentate Lewis acids toward halide ions

Article abstract of DOI:10.1021/om00005a057

¹¹⁹Sn and ¹⁹F NMR spectroscopies were used to study reaction of bis(halodiphenylstannyl)-alkanes (Ph₂XSn)₂(CH₂)_n (X = F, Cl, Br, I; n = 1, 2, 3) with various halide ions in dichloromethane solution. All three series of bis(halodiphenylstannyl)alkanes, (Ph₂XSn)₂-(CH₂)_n (X = F, Cl, Br, I; n = 1, 2, 3), exhibit chelate ability toward halide, forming anionic 1:1 adducts [(Ph₂XSn)₂(CH₂)_nX]^- which are static at -100°C on the NMR time scale. The bis(halodiphenylstannyl)alkanes always preferentially chelate fluoride ion over chloride or bromide. Endocyclic Sn-CH₂ rotation brings about intramolecular exchange between bridging and terminal fluorine atoms at higher temperature. For n = 1, and 1:1 adducts [(Ph₂XSn)₂(CH₂)X]^- react with additional fluoride (but not chloride or bromide) eventually to give [(Ph₂F₂Sn)₂(CH₂)]^2- in which both tin atoms are five-coordinated. For n = 2, the 1:1 adducts [(Ph₂XSn)₂(CH₂)₂X]^- appear particularly stable and there is no evidence for formation of 1:2 adducts [(Ph₂X₂Sn)₂(CH₂)₂] ^2-. Propylene-bridged 1:1 adducts, [(Ph₂XSn)₂(CH₂)₃X]^-, react with both fluoride and chloride to give 1:2 adducts, [(Ph₂F₂Sn)₂(CH₂)₃] ^2- and [(Ph₂Cl₂Sn)₂(CH₂)₃] ^2-, respectively, in which the tin atoms remain five-coordinated. The crystal structures of [(Ph₂FSn)₂CH₂F]^- (1), [(Ph₂BrSn)₂CH₂F]^- (4), [(Ph₂ISn)₂CH₂F]^- (8), and [(Ph₂ClSnCH₂)₂F]^- (11), as their tetraethylammonium salts (1a, 4a, 8a, and 11a, respetively), are described. Colorless crystals of 1a are monoclinic, space group P2₁/n, with a = 11.695(4) A?, b = 14.667(2) A?, c = 18.956(2) A?, β = 103.33(1)°, V = 3164(1) A?³, and Z = 4. Colorless crystals of 4a are monoclinic, space group Cc, with a = 11.758(1) A?, b = 14.880(2) A?, c = 19.316(2) A?, β = 93.981(9)°, V = 3371.3(6) A?³, and Z = 4. Colorless crystals of 8a are monoclinic, space group P2₁/n, with a = 10.032(1) A?, b = 16.923(3) A?, c = 20.523(3) A?, β = 99.65(1)°, V = 3434.9(8) A?³, and Z = 4. Colorless crystals of 11a are monoclinic, space group P2₁, with a = 9.562(2) A?, b = 15.529(4) A?, c = 11.359(4) A?, β = 95.51(2)°, V = 1678.9(9) A?³, and Z = 2. The structures were refined to final R = 0.027, 0.029, 0.033, and 0.029 for 4661, 2647, 3843, and 3457 reflections with I ≥ 3.0σ(I), respectively.