Organotin Sulfonates

The first section, Chemical Reactions on Polymers, deals with aspects of chemical reactions occurring on polymers—aspects relating to polymer size, shape, and composition are described in detail. One of the timely fields of applications comprises the use of modified polymers as catalysts (such as the immobilization of centers for homogeneous catalysis). This topic is considered in detail in Chapters 2, 3, 8, 9, and 11 and dealt with to a lesser extent in other chapters. The use of models and neighboring group effect(s) is described in detail. The modification of polymers for chemical and physical change is also described in detail in Chapters 2 (polystyrene) 4 (polyvinyl chloride) 5 (polyacrylic acid, polyvinyl alcohol, polyethyleneimine, and polyacrylamide) 6 (polyimides) 7 (polyvinyl alcohol) 8 (polystyrene sulfonate and polyvinylphosphonate) 10 (polyacrylamide) and 12 (organotin carboxylates). 

Transesterification of an ester is commonly carried out by heating it with an excess of an alcohol in the presence of a strong acid catalyst such as toluene p-sulfonic acid. On the industrial scale, this presents problems of corrosion and of decomposition and colouration of the excess alcohol. Organotin compounds are alternative catalysts they can be used in small amounts (0.1-0.25%), they present no corrosion problem, and the excess of alcohol is not dehydrated or decolourised, and can be recirculated. 

Organotin carboxylates and sulfonates form an important class among the family of organotin compounds.These compounds possess rich structural diversity. A range of structures from simple mononuclear compounds to complex polynuclear cages and clusters are formed." The structural diversity of these compounds emanates from several features. These include ... 

The theme of this chapter revolves around clusters of organotin carboxylates and sulfonates. For the sake of completion other structural types are mentioned briefly. 

Organotin Carboxylate and Sulfonate Clusters 101 Table 2.4.2 Representative examples of trinuclear diorganostannoxane macrocycles... 

Concerning the oxygen-containing bidentate ligands [R E02+ ] and MC, discrete dimeric, tetrameric and hexameric ring assemblies have been reported for organotin carboxylate, phosphinate, phosphonate monoester, phosphate diester, " sulfonate, and tungstate derivatives. 

Hydrolytically stable organotin compounds are also being prepared with sulfonic acids. " These di-alkyltin and trialkyltin sulfonates can be used in combination with t -amines as catalysts in the preparation of polyurethane foams. 

Advances in techniques include sophisticated NMR methods, both in solution and the solid-state, and computational methods, and these, coupled with X-ray diffraction and other established methods, have been applied to the study of a wide variety of structures. Topics covered in the book include Sn(II) clusters, tin Zintl ions, Sn(II) heterobimetallic compounds, RsSn+ cations, stannylenes (R2Sn ), stannenes (R2Sn=SnR2 and R2Sn=CR2), stannynes (RSn=SnR), organotin oxide, carboxylate and sulfonate clusters, dendrimers and macrocycles, organotin polymers, Sh-tt interactions, unusual bondings and structures, and compounds with non-linear optical properties. 

Organotin hydride/AIBN desulfurization enabled efficient desulfonylation of n-deficient heterocyclic sulfones, which cannot be removed by a conventional method such as use of Al(Hg) and Na(Hg) (Scheme 12.124) [226]. 

Reductive Desulfonylations by Tin Hydrides. Reductive desulfonylation of allyl, vinyl, and a-functionalized sulfones can be carried out employing tin hydrides. This radical reaction is usually promoted thermally or photochemically and provides organotin derivatives as intermediates which are finally subjected to protonolysis (Eq. 32). Both steps can be carried out in one pot employing catalytic amounts of tin. 

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