Organotin carboxylates

Organotin Carboxylates and other Oxyesters. Stannylium Ions 

Organotin carboxylates, R Sn(02CR )4- , are most commonly prepared2 by treating the corresponding oxide or hydroxide with the carboxylic acid (equations 13-1-13-3), or from the reaction of the corresponding chloride with a metal carboxylate (equation 13-4), or by cleaving a tin-carbon bond with a carboxylic acid (equation 13-5) or a mercury or mercury(II), or lead(IV) carboxylate (equation 13-6). 

The first group of reactions (13-1-13-3) can be carried out by mixing aliquots of the tin oxide or hydroxide and acid in a solvent such as methanol (e.g. equation 13-7).3 The water can often be conveniently removed by azeotropic dehydration in benzene or toluene, but with aryltin compounds it may be better to use molecular sieves, to avoid the risk of cleaving the aryl-tin bonds.4 

The products of the reaction of dialkyltin oxides R2SnO (R = Bu, Bu1, Bus, or Bu ) with carboxylic acids R C02H (R = Me, Et, Pr1, or Bu1) (equation 13-8) depend on the size of the groups R and R and on the molar ratios.5 

R2Sn(02CR )2 or (R C02)R2Sn0SnR2(02CR ) or R2Sn(0H)02CR (13-1) (13-2) (13-3) 

The structural chemistry of organotin carboxylates has been thoroughly reviewed [419, 420] and only a brief survey of self-assembled supramolecular systems will be presented here. 

Triorganotin carboxylates tend to be monomers (.142 and 143) only with aromatic carboxylic acids (substituted benzoates) or with bulky substituents at tin (e.g. Ph or Cy) [420]. Most other organotin carboxylates are supramolecular aggregates, usually chain polymers with carboxylato bridging. 

In the polymers tin becomes live-coordinated, trigonal bipyramidal, with the oxygen atoms in axial positions. Intra-unit Sn- -O distances are ca. 3.0 A, which suggests very weak interaction, and in many crystal structure determinations they were simply ignored. They usually distort the trigonal bipyranaidal geometry, however. 

It has been shown by Sn Mossbauer spectral studies [416] that the supra-molecular self-assembly is maintained in solution. 

A selection of structurally characterized triorganotin carboxylates is listed in Table 3.13, in order of complexity of the organic groups at tin. The Sn-O and Sn O bond lengths and O-Sn O axial bond angles are given. 

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The organotin maleate and maleate half-ester derivatives also exhibit this bleaching effect reportedly by a Diels-Alder addition reaction (18). The reaction is specific to the organotin maleates other organotin carboxylates containing normal dieneopltiles fail to produce similar results (19). 

The resulting derivatives, unlike most organotin carboxylates, are hydrolyzed relatively readily in air. An X-ray crystallographic study 399) showed that trimethyltin glycinate has an intermolecularly associated, polymeric structure, with bridging amino groups. 

SEC-RI/UV has also been used to analyse some 26 thioorganotin compounds, organotin carboxylates and chlorides, essentially PVC stabilisers, and some of their main by-products and related compounds (thioesters and dithioesters, n-alkanes) [803]. Not all organotin chlorides were stable in the adopted analysis conditions. N, Ai -ethylene-bis-stearamide and -oleamide in common plastics (ABS, SAN, PUR, LDPE, PA6.6) can be analysed by SEC after derivatisation with trifluo-roacetic anhydride. SEC analysis of fatty alcohol ethoxy-lates (FAE), used as nonionic surfactants, has also been described [759]. 

Complex formation in binary systems under the influence of organotin monomers (organotin carboxylate and epoxide monomers) was studied by IR and NMR techniques 2,3,18 -23). 

Organotin carboxylates (R3SnOOC—R ) are applied to metal surface as a thin layer and hardened by heating to high temperatures (about 400 °C)69). 

Then, it appears, that photochemical cross-linking of an organotin copolymer is the result of complex supramolecular conversions and intermoleeular reactions of anhydride and organotin units involving the formation of transverse coordination-bound organotin carboxylate fragments 109). 

A large variety of organotin carboxylates have been prepared, and their structures determined by X-ray diffraction. Part of the impetus for this work has been the search for anticancer drugs, and the aim of relating activity to structure. The early work on structure has been thoroughly reviewed,346 as well as recent developments,347 including the structural work on the organotin derivatives of amino acids and peptides.348... 

Structure, Mechanism, and Reactivity of Organotin Carboxylate Polymers... 

Antifouling performance of these organotin carboxylate polymers indicates that their mode of action corresponds to the bulk abiotic bond cleavage model proposed by Castelli and Yeager (8). The controlling factors to be considered here are ... 

Antifouling performance of organotin carboxylate polymers show that their mode of action corresponds to the "bulk abiotic bond cleavage" model. All the controlling factors are analyzed. 

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). 

An added advantage of these esters is the ready transformation into other esters by alkylation of the intermediate organotin carboxylates in the above reaction. 

The organotin carboxylates may adopt a variety of structural modes depending on the nature of the organic substituent on the tin atom and/or the carboxylate... 

The tin-oxygen interatomic distances present in organotin carboxylates were classified in terms of primary Sn—O covalent bonds ca 2.0 A), slightly longer dative Sn—O bonds (ca 2.2-2.3 A) and Sn- -O secondary interactions (>2.5 A)214. Triorganotin carboxylates can adopt the three idealised structure types 124a-c. 

Organotin carboxylates are generally available from the oxides (or hydroxides) on reaction with the carboxylic acid (equation 98), or from the organotin halides with sodium carboxylates (equation 99). Electrophilic cleavage of the... 

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