Tin IV and Organotin Halides

Formation of Tin-Transition or Inner Transition-Metal Bond 5.8.5.3. from Tin(IV) and Organotin Halides... 

In basic aqueous media, a kinetic study of the reaction between stannate(II) ions and alkyl halide shows that mono- and disubstituted organotin compounds are formed (Eq. 6.12a).27 The monosubstituted organotin compound is obtained after a nucleophilic substitution catalyzed by a complexation between the tin(II) and the halide atom. The disubstituted compound results from an electrophilic substitution coupled with a redox reaction on a complex between the monosubstituted organotin compound and the stannate(II) ion. Stannate(IV) ions prevent the synthesis of the disubstituted compound by complexation. Similarly, when allyl bromide and tin were stirred in D2O at 60° C, allyltin(II) bromide was formed first. This was followed by further reaction with another molecule of allyl bromide to give diallyltin(IV) dibromide (Eq. 6.12b).28... 

The most substantial study of this sort, analysing structures of 186 four-, five- and six-coordinated tin compounds, was published by Britton and Dunitz (1981) under the memorable title Pathways for SN2 and SN3 Substitution at Sn(IV) . Organotin halides readily increase their coordination number to 5 or 6 (Davies and Smith, 1982), and a wide range of structures are stable in the solid state. 

Reactions of tin(IV) halides or organotin halides with organic derivatives of more electropositive metals provide the most important general synthetic routes to carbon-tin bonds (equation 6). The most frequently used R -M compounds are those of magnesium and lithium, with sodium, zinc, and aluminum having a more limited use. Some examples of these reactions are given in equations (7-9). 

Alkyl and aryltin(IV) diphenyldithioarsenates R Sn(S2AsPh2)4 ( = 2, R = Me, Bu , Ph = 3, R = Me, cy, Ph) are available from the organotin halides and the sodium salt of diphenyldithioarsenates. The dialkyl and trialkyltin species are four-coordinate by spectroscopy whereas the phenyl derivatives are six-coordinate. A structural study of Me2Sn(S2AsMc2)2 reveals a four-coordinate tin center with monodentate coordination of the dithioarsenate." ... 

The acidity of the cyclopentadienes makes the cyclopentadienyltin compounds readily accessible97 either through the reaction of other cyclopentadienylmetal derivatives with tin(IV) halides (equation 9-44),99 or by acidolysis of an aminostannane with a cyclopentadiene (equation 9-45).100 101 Ferrocenylstannanes can also be obtained from ferrocenylmercury compounds and organotin sulfides (equation 9-54).102... 

One of the more commonly used organotin reagents in both free-radical reactions and Lewis acid-mediated reactions is allyltributyltin [3, 7]. This reagent permits the construction of new carbon-carbon bonds from free radical precursors such as alkyl halides however, reactions with a-ketocydopropanes were poorly understood. Tin(IV) enolates generated from a-ketocyclopropane 44 and allyltributyltin undergo both radical allylation and electrophilic quench as shown in Scheme 11, forming O-stannyl ketyl 45 with allyltributyltin and subsequent scission of the cyclopropane... 

The normal targeted products of reactions between tin (IV) halides and organomagnesium or organolithium reagents are the tetraorganotins, as it is difficult to control alkylation sufficiently well to a lower extent. However, controlled reactions can be achieved in certain cases, e.g. when bulky groups are present (such as cyclohexyl) or when an organotin halide product can be stabilized by chelation (equation 10). 

The Kocheshkov redistribution reaction between tetra-organotins and tin(IV) halides, in appropriate mole ratios, is a general method of synthesis of organotin halides (equations 59 and 60). It is a particularly useful reaction, since it is difficult to control the alkylation of SnX4 by organolithium or Grignard reagents to the desired extent. 

Another very widely used synthesis of the organotin halides involves the proportionation reaction between tetra-organotins and tin(IV) halidesi . In these reactions, illustrated below, it is to be noted that there is conservation ofthe whole organic content of the reaction as the required organotin halide, in contrast to the losses of organic groups in the above equations. 

The attractive proportionation reaction between tetra-organotins and tin(I V) tetrahalides for the preparation of organotin halides is of little use in organolead chemistry, as the low thermal stability of organolead halides and the lead(IV) halides does not allow the temperature range of these proportionations to be reached, except in a few special cases os. 

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