Organotin Lewis acid

To be complete one should add the extremely rich tin hydride chemistry, or the halodestannylation reaction as well as the creation of various carbon-heterode-ment bonds. We should also add the use of tin oxides or hydroxides as protecting groups in polyol chemistry, the use of organotins as catalysts for many reactions such as transesterifications or amide formation. Finally, we could also mention the use of optically active organotin Lewis acids as efficient chirality inductors. All of these reactions, which are not covered in this chapter tend to prove that the use of organotins for organic synthesis is now undoubtedly established and is not limited to the carbon-carbon bond formation with the aforementioned reactions. 

Ultimately, as the stabilization reactions continue, the metallic salts or soaps are depleted and the by-product metal chlorides result. These metal chlorides are potential Lewis acid catalysts and can greatiy accelerate the undesired dehydrochlorination of PVC. Both zinc chloride and cadmium chloride are particularly strong Lewis acids compared to the weakly acidic organotin chlorides and lead chlorides. This significant complication is effectively dealt with in commercial practice by the co-addition of alkaline-earth soaps or salts, such as calcium stearate or barium stearate, ie, by the use of mixed metal stabilizers. 

Group 14 metal halides also undergo metathesis reactions. For instance, organotin compounds are prepared on an industrial scale using organoaluminum reagents. These reactions take place because tin is a softer Lewis acid than aluminum, and carbon (in an alkyl group, represented by R) is a softer Lewis base than chlorine ... 

Organotin(IV) compounds are Lewis acids. The crystalline structure of Lewis acid-base adducts between compounds R SnCl4- (/ = 0,..., 3) and Ni complexes with Schiff bases was determined by XRD, 119Sn Mossbauer and IR spectroscopy. Adducts are formed in 1 1, 1 2 and 2 1 ratios121. 

Complex with a chloride salt. The organotin compound is a powerful bidentate Lewis acid, binding the chloride ion. 

Pentadienyltrimethylstannanes undergo regioselective conjugate additions to aldehydes, catalysed by Lewis acids. The dominant product obtained depends on the catalyst used, as shown in reaction 46. In the case of titanium tetrachloride catalysis the reaction is also stereoselective and only one diasteroisomer is obtained297. Reaction with chiral aldehydes leads to asymmetric induction with similar organotin compounds298. 

Besides the silyl enolate-mediated aldol reactions, organotin(IY) enolates are also versatile nucleophiles toward various aldehydes in the absence or presence of Lewis acid.60 However, this reaction requires a stoichiometric amount of the toxic trialkyl tin compound, which may limit its application. Yanagisawa et al.61 found that in the presence of one equivalent of methanol, the aldol reaction of an aldehyde with a cyclohexenol trichloroacetate proceeds readily at 20°C, providing the aldol product with more than 70% yield. They thus carried out the asymmetric version of this reaction using a BINAP silver(I) complex as chiral catalyst (Scheme 3-34). As shown in Table 3-8, the Sn(IY)-mediated aldol reaction results in a good diastereoselectivity (,anti/syn ratio) and also high enantioselectivity for the major component. 

The structural chemistry of the organotin halides is dominated by their Lewis acid properties and their propensity to form five- and six-coordinate complexes. Self-association may give oligomers or polymers in the solid state, which usually dissociate in solution. The structure of tricyclohexyltin chloride in the crystal is temperature-dependent. At 108 K, it has the form of a rod-like polymer with distorted trigonal-bipyramidal tin and Sn-Cl separations of 245.6(7) and 300.77(7) pm, but at 298 K, the structure is best regarded as consisting of near-tetrahedral discrete molecules.3... 

An additional entirely selective condensation synthesis for asymmetric TTF molecules is based on strategy S6, which consists in the reaction of an organotin dichalcogenolate with an ester in the presence of a Lewis acid such as MesAl (Yamada et al, 2004). A scheme of the reaction is given in Fig. 2.7. The method applies to the preparation of varied asymmetric IT Fs and can also be extended to the synthesis of selenium-containing analogues. 

It is known that the geometries of the reactants play an important role in the regio-and stereochemical outcome of radical reactions since they are commonly involved in early transition states. Previous attempts to affect rotamer populations during the reaction included, among others, control of temperature and addition of a Lewis acid. It was recently reported75 that organotin halides, common byproducts of radical reactions, act... 

A very unusual mixed-metal receptor has been prepared by Jurkschat and co-workers [68]. Macrocycle 102 comprises two ferrocene reporter units linked together by two Lewis acidic organotin spacers. Electrochemical measurements in dichloromethane solution show anion-induced cathodic shifts of the ferrocene/ferrocenium redox couple of 130 mV for chloride, 210 mV for fluoride and 480 mV for dihydrogenphosphate. 

The transmetalation of organotin derivatives to their indium counterparts (Scheme 1) has recently been used to investigate a new route to Group 13 polyfunctional Lewis acids, which are becoming important in catalysis, molecular recognition, and materials synthesis. ... 

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