Distannoxanes structures

A new cation-anionic complex of hypercoordinate tin (593) was obtained by treatment of (L5)2SnCl2 (L5 is a bidentate (2-oxopyrrolidino)methyl C,0-chelating ligand) with AgBF41250. As in the case of (L7)2GeCl2 (Section VIII.A), the reaction occurs with replacement of both Cl atoms. As shown by X-ray crystallography, the reaction product, however, has a dimeric distannoxane structure, in which both tin atoms are stannacenium... 

Control of Distannoxane Structure by Silicon-Containing Spacers... 

The solid-state structure of tetrabutylbis(2,3 4,6-diisopropylidene-2-keto-L-gulonato)distannoxane has been determined. The [Bu2Sn(IV)] complex of D-lactobionic acid also proved to be oligomeric, containing octa- (within the chain) and pentacoordinated (at the end of the chain) Sn centers in a ratio of 2 4. ... 

Unless the organic groups are very large, the difunctional distannoxanes are dimeric in the solid state, with all the tin atoms rendered at least five coordinate. The two most common structural motifs are represented by the dichloride 37, where there are two four-membered rings about the central distannoxane core, and the dicarboxylate 38, where there are four six-membered rings about the center, but a number of variants on these basic models have been identified.347... 

If bridged bis(dichlorodistannoxanes), X2RSn SnRX2, are converted into the distannoxanes (usually by reaction with Buc2SnO), the products have a more complex structure, with the alternatives shown in Equation (134). 

The 119Sn chemical shifts for the distannoxanes provide evidence for the existence of a dimeric ladder structure [9] in solution. (73) The tetrabutyl-dichloro- and -dibromo-distannoxanes and tetramethyl-bis-(trimethylsiloxy)distannoxane show two well-resolved u9Sn signals... 

High dilutions reduced the amount of oligomers formed. Preliminary experiments on enantio-enriched hydroxyl esters 20.6 and 20.7, using distannoxane transesterification catalyst, produced stereochemically diverse homo- and heterodimers 20.8-20.10. Functionalization of the macrodiolides was investigated in an effort to create additional structural diversity. Electrophilic epoxidation of macrodiolide 20.9 afforded bis-epoxide 20.11. Further diversification was achieved by treating the macrodiolide bis-epoxide with DBU, which resulted in epoxide ring opening to afford a,P-unsaturated macrolide 20.12. 

Componnds 8 and 9 are associated as dimers via O Sn interactions there are intermolecnlar O Sn distances (2.327 and 2.587 A) approximately trans to S (angle 150.6°) and N (angle 146.92°) with a symmetrical distannoxane Sn202 nnit. In addition, there are intramolecnlar O Sn bonds (2.679 A with HOCH2CH2S ligands in 8) and transannnlar N Sn bonds (2.224 A in 9) and the tin coordination is raised to 6. Only one signal at 28.7 ppm is observed in the Sn NMR spectrum of 8, which is within the range for the four-coordinated tin nucleus. Therefore, the structure of 8 in solution is... 

The difunctional distannoxanes XRjSnOSnR X have been reported to be particularly effective catalysts, and this has been rationalized in terms of their dimeric structure (XR2SnOSnR2X)2 , but at a tin concentration of 4 x 10 moldm", the catalytic reactivity for the addition of BuOH to PhNCO is in the order Bu2Sn(OAc)Cl > AcOBu2SnOSnBu2Cl > Bu2Sn(OAc)2 > AcOBu2SnOSnBu20Ac °. 

The X-ray crystal structures of many of these dimeric distannoxanes have now been determined 28 examples are listed in the first edition of this book many more have now been described, and details can be retrieved from the database on the CD ROM that accompanies this second edition.82 All have the common feature of dimerisation to give a central SnOSnO ring as shown in 12-17, but the detailed structures depend on the identity of the groups X.83... 

These preliminary results show that the silicon-containing spacers play an essential role in controlling the structure of the distannoxane dimers 7,8a, and 8b. 

Poly(l,4-cyclohexylenedimethylene succinate) (PCDS) (Figure 6.2), can be produced by the distannoxane-catalyzed polycondensation of succinic acid and 1,4-CHDM (18). The crystal structure of frans-PCDS studied by X-ray and electron diffraction revealed that this polyester crystallizes with a unit cell ofa = 0.649 nm, b = 0.948 nm and c = 1.351 nm, and P = 49.5° in the space group Pljn (19,20). 

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