14540-08-0Relevant academic research and scientific papers
Wurtz-type reductive coupling reaction of allyl bromides and haloorganotins in cosolvent/H2O(NH4Cl)/Zn media as a route to allylstannanes and hexaaryldistannanes
Von Gyldenfeldt, Friederike,Marton, Daniele,Tagliavini, Giuseppe
, p. 906 - 913 (2008/10/08)
Twenty-one allylstannanes have been prepared via a simple Wurtz-type coupling reaction of allyl bromides and R3SnX compounds (R = Me, Et, Pr, Bu, Ph; X = Cl, I, OH), Bu2SnCl2, and (Bu2SnCl)2O in cosolvent/H2O (NH4Cl saturated) media under the mediation of zinc powder. Also R3SnSnR3 compounds (R = Ph, p- and m-Tol) have been prepared via coupling of triaryltin chlorides. The stereochemical course of the reaction between R3SnCl and (C4H7)Br (C4H7 = α-methylallyl, trans- and cis-crotyl) has been extensively studied. Two distinct reactions are involved in the overall process: (i) the coupling reaction, which gives rise stereoselectively to the sole R3SnCH(CH3)CH=CH2 (α-isomer), and (ii) the subsequent isomerization of the α-isomer furnishing mixtures of (α, trans, cis)-isomers. The occurrence of reaction ii depends upon the nature either of the R group or the employed cosolvent. In cyclohexane, the α-isomer is exclusively obtained with R = Bu, while with R = Me, Et, and Pr it is found as a major component in the ternary isomeric mixture. In tetrahydrofuran, 2-propanol, acetonitrile, and pyridine, the isomerization occurs to an extent which depends on the polarity and the coordinating ability of the cosolvent itself. The observed stereoselection has been hypothesized to occur through one-electron transfer from the zinc metal to the (C4H7)Br to form stereoselectively an adsorbed CH2=CHCH(CH3)Br?-Zn?+ radical ion which is trapped by the R3SnCl reactant to form the α-isomer. Similarly, ditin compounds are thought to be formed by interaction of R3SnCl?-Zn?+ radical ions with R3SnCl molecules.
Allyl- and allyl-like-tin derivatives. 3. Crystal structures and solution conformations of some cyclohex-2-enyl- and cyclohept-2-enylstannanes
Kitching, William,Penman, Kerry G.,Valle, Giovanni,Tagliavini, Giuseppe,Ganis, Paolo
, p. 785 - 790 (2008/10/08)
The crystal structures of the allylic stannanes cyclohex-2-enyl- (1) and cyclohept-2-enyltriphenylstannanes (2) have been determined, and in both, the coordination about tin is tetrahedral, although the enlargement of the 〈C(13)-Sn-C(19) angle in both 1 (114.4°) and 2 (117.0°) may be in response to a short intramolecular contact between one phenyl ring and the cycloalkene moiety. The Sn-C(phenyl) bond lengths are normal (2.144 ± 0.005 A?), but the allyl bond (Sn-C(19) = 2.185 ± 0.005 A?) is longer (ca. 0.04-0.05 A?) than the normal Sn-C(aliphatic) bond length (2.13 ± 0.01A?) and may be associated with a hyperconjugative σC-Sn-π effect. In 1, the (C6H6)Sn group formally occupies a quasi-equatorial orientation with a Sn-C(19)-C(20)-C(21) torsion angle of 121° which permits substantial σ-π interaction and may best accommodate other interactions in the crystal. Given the other values of bond and torsion angles, the actual distinction between quasi-axial and quasi-equatorial orientations with respect to double bond interaction with δC-Sn is a fine one. The molecular geometry of 2 is a slightly distorted chair arrangement with the (C6H5)3Sn group clearly occupying a quasi-axial position with a Sn-C(19)-C(25)-C(24) torsion angle of 90°, the most favored for σ-π interaction. However, this outward splaying of the C-Sn bond is probably also associated with relief of interactions between Sn(C6H5)3 and the regions of C(21) and C(23). Solid-state (MAS) 13C NMR spectra have been recorded of both 1 and 2, and although only one set of signals was observed for each, 119Sn-13C couplings were not located. 1H and 13C NMR spectra for 1 and 2 (in solution) have been obtained, and for 1 there is now a preponderance of the conformer with an axially disposed tin group, whereas for 2, the solution conformation is adequately described as a distorted chair arrangement with a quasi-axial Sn(C6H5)3 group, as identified in the crystal.
