Distannoxanes dimeric

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. 

A number of molecules have been described involving bonds between tin and various types of CN group. The tetramethyl-l,3-di-isothiocyanato-distannoxane dimer contains two types of tin atom, both in trigonal-bipyramidal sites with (Me2SnO) equatorial groups but with different axial... 

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... 

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... 

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... 

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... 

Figure 2.5.3 Frequent tin-containing secondary building units (SBUs) that can be used for the generation of macrocyclic or extended supramolecular assemblies (a) Sn202 dimers (b) Sn402X2Y2-distannoxanes (c) Sn Oe drums...

A more convenient method for 1 was developed starting from commercially available Ph2SnCl2. All fluoroalkyldistannoxanes thus prepared were isolated as crystalline materials, and Sn NMR spectra gave rise to two distinct resonances diagnostic of the characteristic dimeric distannoxane formulation. 

Related dimeric supramolecular aggregates can be obtained with other terminal funetional groups, e.g. j6-diketonates, in the distannoxanes an example is the (ben-zoyltrifluoroacetonato)(trifluoroacetato)tetramethyldistannoxane dimer [383]. This chemistry has not been pursued further. 

Complex (a) was isolated as a dimer. Carbon dioxide uptake was found to be reversible at room temperature and consists of the insertion of carbon dioxide into Sn-OiPr bond to form a monodentate allq lcarbonato ligand. Notably, an identical structure was characterised from [(CH3)2Sn(OCH3)2]2, which is also active for dimethyl carbonate formation in an excess of methanol and carbon dioxide at 180 °C and 30 MPa. In the distannoxane series, the structure of the isolated species (b) is also dimeric with a similar insertion of carbon dioxide into a Sn-OiPr bond to form a monodentate allq l carbonate ligand. Species (c) has a higher nuclearity of 10 tin atoms. 

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