- Wurtz-type reductive coupling reaction of allyl bromides and haloorganotins in cosolvent/H2O(NH4Cl)/Zn media as a route to allylstannanes and hexaaryldistannanes
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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.
- Von Gyldenfeldt, Friederike,Marton, Daniele,Tagliavini, Giuseppe
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p. 906 - 913
(2008/10/08)
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- Ueber gemischte Gruppe 14-Gruppe 14-Bindungen. IV. Hexa-p-tolylethan-Analoga p-Tol6Sn2, p-Tol6PbSn und p-Tol6Pb2: Darstellung, Homoeotype Structuren, NMR-Kopplungen und Valenzschwingungen
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p-Tol6PbSn has been synthesized by reaction of p-Tol3PbLi with p-Tol3SnI in THF/ether (1:2) at -78 deg C.The crystal structures of p-Tol4Pb (I) and of p-Tol6Sn2, p-Tol6PbSn and p-Tol6Pb2 have been determined.The three dinuclear compounds crystallize not strictly isomorphous.They exhibit the same space group (R) and rather similar unit cell dimensions.Yet according to the solvent of crystallization, two types with differing atomic position parameters can be distinguished ( homoeotypism with differences of parameters in the definition of Laves).In both types, the individual molecules have a chiral C3-symmetric conformation and the non-chiral unit cell encloses both enantiomers.The metal-metal distances are Sn-Sn = 2.777(1), Pb-Sn = 2.813(2) and Pb-Pb = 2.851(1) Angstroem, NMR (13C, 119Sn, 207Pb) and Raman data are given (1J(119Sn- 119Sn) = 4570, 1J(119Sn-207Pb) = 3640 Hz; ν(Sn-Sn) = 131, ν(Pb-Sn) = 114, ν(Pb-Pb) = 105 cm-1).
- Schneider, Claudia,Draeger, Martin
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p. 349 - 362
(2007/10/02)
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