Lihung Pu

Substituent effects in ditetrel alkyne analogues: multiple vs. single bonded isomers

The synthesis and characterization of a series of digermynes and distannynes stabilized by terphenyl ligands are described. The ligands are based on the Ar′ (Ar′ = C6H3-2,6(C6H3-2,6-iPr2)2) or Ar* (Ar* = C6H3-2,6(C6H2-2,4,6-iPr3)2) platforms which were modified at the meta or para positions of their central aryl rings to yield 4-X-Ar′ (4-X-Ar′ = 4-X-C6H2-2,6(C6H3-2,6-iPr2)2, X = H, F, Cl, OMe, tBu, SiMe3, GeMe3) and 3,5-iPr2-Ar′ or Ar* and 3,5-iPr2-Ar*. The compounds were synthesized by reduction of the terphenyl germanium(II) or tin(II) halide precursors with a variety of reducing agents. The precursors were obtained by the reaction of one equivalent of the lithium terphenyl with GeCl2 dioxane or SnCl2. For germanium, their X-ray crystal structures showed them to be either Ge–Ge bonded dimers with trans-pyramidal geometries or V-shaped monomers. In contrast, the terphenyl tin halides had no tin–tin bonding but existed either as halide bridged dimers or V-shaped monomers. Reduction with a variety of reducing agents afforded the digermynes ArGeGeAr (Ar = 4-Cl-Ar′, 4-SiMe3-Ar′ or 3,5-iPr2-Ar*) or the distannynes ArSnSnAr (Ar = 4-F-Ar′, 4-Cl-Ar′, 4-MeO-Ar′, 4-tBu-Ar′, 4-SiMe3-Ar′, 4-GeMe3-Ar′, 3,5-iPr2-Ar′, 3,5-iPr2-Ar*), which were characterized structurally and spectroscopically. The digermynes display planar trans-bent core geometries with Ge–Ge distances near 2.26 A and bending angles near 128° consistent with Ge–Ge multiple bonding. In contrast, the distannynes had either multiple bonded geometries with Sn–Sn distances that averaged 2.65 A and an average bending angle near 123.8°, or single bonded geometries with a Sn–Sn bond length near 3.06 A and a bending angle near 98°. The 3,5-iPr2-Ar*SnSnAr*-3,5-iPr2 species had an intermediate structure with a longer multiple bond near 2.73 A and a variable torsion angle (14–28°) between the tin coordination planes. Mossbauer data for the multiple and single bonded species displayed similar isomer shifts but had different quadrupole splittings.

The synthesis and structure of sterically encumbered terphenyl tin(II) halide derivatives: simultaneous existence of monomers and dimers in the crystalline phase

Abstract The reaction of Et2O·LiC6H3-2,6–Trip2 (Trip=C6H2–2,4,6-i-Pr3) with SnCl2 afforded the two coordinate monomer Sn(Cl)C6H3-2,6–Trip2 (1), and its dimer {Sn(μ-Cl)C6H3–2,6-Trip2}2 (2), as orange and yellow crystals, respectively. Solution 119Sn NMR spectroscopy of 2 in C6D6 solution showed that it dissociated readily to give 1. The addition of pyridine (py) to a solution of 1 yielded the adduct py·Sn(Cl)C6H3–2,6-Trip2 (3) which featured tin in a three coordinate pyramidal environment. The reaction of the closely related bulky terphenyl lithium reagent LiC6H3–2,6-Dipp2 (Dipp=C6H3–2,6-i-Pr2) with SnCl2 afforded the mixed halide species {Sn(μ-Cl)0.35(μ-I)0.65C6H3–2,6-Dipp2}2 (4). This arose from the preparation of the lithium aryl precursor in situ from IC6H3–2,6-Dipp2 and n-BuLi. The monomeric nature of 1, and the weak association of 2 and 4, were attributed to the large size of the terphenyl ligands. All compounds were characterized by X-ray crystallography, 1H, 13C and 119Sn NMR spectroscopy, and IR and UV–Vis spectroscopy.

Synthesis and structural characterization of (THF)3Na{(SnC6H3–2,6-Trip2)2} (Trip=C6H2-2,4,6-i-Pr3): effects of cation–anion association on Sn–Sn multiple bonding

The synthesis and structural characterization of the contact ion-pair species (THF) 3 Na{(SnC 6 H 3 –2,6-Trip 2 ) 2 } ( 1 ) are described. The compound 1 was synthesized by the reduction of Sn(Cl)C 6 H 3 –2,6-Trip 2 with sodium anthracenide in THF. Its UV–vis and EPR spectra are very similar to those previously reported for the solvent separated ion pairs [K(THF) 6 ] [(SnC 6 H 3 –2,6-Trip 2 ) 2 ] and [K(dibenzo–18–crown–6)(THF) 3 ] [(SnC 6 H 3 –2,6-Trip 2 ) 2 ]. The X-ray crystal structure of 1 reveals an Sn–Sn distance 2.8107(13)A and an Na–Sn bond length of 3.240(7)A with C–Sn–Sn angles of ca. 98°. The Sn–Sn distance and tin geometry are very similar to those previously observed. These similarities lead to the conclusion that the Sn–Sn bonding is affected only in a minor way by sodium coordination. Crystal data at 130 K with CuK α ( λ =1.54178A) radiation; 1 , a =22.142(5), b =15.845(4), c =23.425(7)A, β =107.83(2)°, Z=4, monoclinic, space group C 2/ c , R 1=0.0615 for 4872 ( I =2 σ ( I )) data.

Reduction of Ge(Cl)C6H3mes2-2,6 togive the cyclotrigermenyl radical(GeC6H3mes2-2,6)3· andthe trigermenyl anion saltK(GeC6H3mes2-2,6)3

Treatment of Ge(Cl)C 6 H 3 mes 2 -2,6 1 with 1 equiv. of KC 8 furnishes the new cyclotrigermenyl radical (GeC 6 H 3 mes 2 -2,6) 3 ·, 2) which is characterized by EPR and X-ray crystallography; reduction with a further equivalent of KC 8 gives the new trigermenyl allyl anion analogue K(GeC 6 H 3 mes 2 -2,6) 3 which has an open Ge 3 framework with a wide Ge–Ge–Ge angle of 159.19(10)°at the central Ge and a Ge–Ge distance of 2.422(2) A.