Associative organotin polymers

These empirical observations confirm that primary supramolecular associates typical of conventional polyelectrolytes rather than individual intermolecular interactions exist in organotin polymer solutions. 

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... 

Dumartin and associates described the preparation of in situ polymer-supported organ-otin hydrides for use as clean reducing agents (equation 15)47, while Deleuze and coworkers reported the preparation of a novel, macroporous polymer-supported organotin hydride (37), for use in catalytic free-radical reductions (equation 16)48,49. 

Recent research at Bell Laboratories has shown that defect sites play a dominant role under some conditions. This conclusion is based on the discovery that stability enhancements ranging up to a factor of 9 can be produced by the prior reaction of PVC with a number of organo-tins (22,23,24,25). These enhancements are associated with the incorporation of only a few organotin ligands into the polymer (22, 23,24,25), and they cannot be ascribed to morphological changes since they are observed in solution (25) as well as in bulk (22,23,24,25). Several other possible explanations are excluded by the available facts, and it now seems that the stability enhancements must result from the chemical deactivation of defect structures (22,23,24,25). However, the reason for the residual instability of the modified polymers is not known at the present time (22,23). 

Here we will look at some findings that highhght potential modes of activity as well as problems associated with looking at organotin activity. Further, essentially no mechanistic studies have been carried out on tin polymers, so results from studies of small molecule-containing organotin agents will be examined. 

Some triorganotin carboxylate structures, in particular those containing two RsSn moieties, deserve additional comment because their structures are more varied. For example, rare types of organotin carboxylates include derivatives of carborane-carboxylic acids [ (l,7-C2BioHn-l-COO)Bu2Sn 20]2 (structure of type A) [451]. The bis(triphenyltin) derivative of phenylmaleic acid, 145, contains only four-coordinate tetrahedral tin (Sn O 2.077 and 2.090 A) and is not associated, but in the bis(triphenyltin) citraconate, 146, one tin atom participates in the supramolecular association, 147, and polymer-chain formation and becomes five-coordinate (trigonal pyramidal Sn-O 2.193 A, Sn O 2.397 A) whereas the second remains four-coordinate (Sn-O 2.089 A), as a part of a dangling side chain [441]. 

Organotin compounds with Sn-S bonds can be prepared by substituation at tin by sulfur nucleophile. There are many parallels between the chemistry of compounds containing Sn-S bonds and those containing Sn-0 bonds. An important difference between them is that whereas Sn-0 bonded compounds often self-associate to give oligomers or polymers with 5-coordinate tin, the sulfur compounds show fewer tendencies to associate. The Sn-S bonds also less easily cleaved in substitution (e. g. hydrolysis) and addition reactions [54,56]. 

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