Organotin/halides

The organotin halides R SnX4 provide the starting materials from which most other functional organotin compounds R SnY4 (Y = H, OR, NR 2, OCOR etc.) are prepared (see Chapter 1), and a number of the halides are available commercially. 

The direct reaction between an organic halide and tin metal or a tin(II) halide. 

The reaction of a tetraorganostannane with a halogen X2, halogen acid HX, or metal halide (MX , e.g. M = Hg). 

The reaction of an organotin hydroxide or oxide with a halogen acid, HX, or acid halide. 

The first two of these reactions have been adequately described in Sections 4.1, 4.3, 5.3, and 7.1. We are concerned here with the other five methods. 

Among the organotin halides, as suggested by the intermolecular bond distances in associated structures, only fluorides seem to contain dative bonds. The chlorides 

Compound and ref. Form of association Sn-F bond length (A) Sn —F bond length (A) Sn-F-Sn bond angle (°) 

Triorganotin fluorides form polymeric chains in the solid state. The tin atom is five-coordinate and has trigonal bipyramidal geometry, with the halogen atoms in axial positions. 

Some triorganotin fluorides have been found to be monomeric, 120, and the bond length of 1.961 A in trimesityltin fluoride has been suggested as a standard value for the single covalent Sn-F bond [346]. 

Except for the unusually high value initially reported for tricyclohexyltin fluoride (Sn-F 2.45 A) [347], in other monomeric triorganotin fluorides the observed Sn-F interatomic distances are similar (see Table 3.12). It was recently demonstrated that this figure is wrong, that the correct value is 2.051 A, and that the structure is asymmetric, with a second, dative Sn — F intermolecular bond of 2.303 A [348]. In trimethyltin fluoride a bent chain structure was reported in an early determination of crystal structure [349]. The Sn-F bond lengths, however, differ very little. 

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Perfluorovinyl organotin compounds can be prepared from perfluorovinyl Grignard reagents and organotin halides [76] (equation 11) Yields are slightly improved under Barbier conditions [76]... 

The alkylation of tin tetrachloride with organolithium compounds, Grignard reagents, or organoaluminum compounds remains the most common route to tetraalkyltins, and thence, by the Kocheshkov disproportionation, to the various organotin halides. 

By reaction with the appropropriate aryl halides can be prepared a variety of aryltin compounds that are not accessible from the reactions involving arylmagnesium halides and organotin halides (88,89) there is evidence that an aryne intermediate may be involved (90). However, for some purposes, such as the addition to carbonyl compounds, ox-iranes, and oxetanes, to give hydroxyalkyltin compounds, the Sn-Mg reagents may have advantages (see Section II,E) (91-93). 

Organotin enamines can be prepared by treating organotin halides with the lithium or magnesium derivatives of enamines, and also by treating distannazanes with tin enolates (222,223). 

Covalent Organotin Halide, Pseudohalide, Carboxylate, and Nitrate Complexes... 

Organotin halides are versatile reagents for which many derivatizing schemes can be devised. Trace analysis of organotin componds in environmental samples often involve halostannanes, as was discussed in Section in. 

Organotin hydrides R SnI L- , where R represents an alkyl or aryl group, are generally prepared quite easily by reduction of the corresponding organotin halides using either LiAlFLt or NaBFL in ether or dioxane ... 

An application of the reduction method of organotin halides by simple organotin hydrides is the preparation of l, >-bis(hydridodimethylstannyl)alkanes235 ... 

The synthesis of organotin halides is of paramount importance for organotin chemistry, because these compounds are considered as the starting materials for the preparation of a great number of organotin substances. 

The oldest method for the synthesis of the organotin halides is the reaction of alkyl or aryl halides with elemental tin. This reaction exhibits numerous variants and uses a wide variety of catalysts however, yields are usually unsatisfactory and the method is no longer common nowadays. 

Dimethyltin dichloride can be synthesized from methyl chloride, tin(II) chloride and molten tin. The reaction proceeds in high yields in NaAlCLt melt359. High yields in tri-organotin halides are also obtained from tin and lower alkyl halides, provided an equimolar amount of halide is added to the reaction medium360. 

Other syntheses of functional organotin halides include that of /J-chlorovinyltin compounds330 ... 

Redistribution reactions are considered as quite important for the preparation of alkyltin halides having mainly identical alkyl groups. Actually, the redistribution reactions are halogenation reactions of organotin halides by SnX4 (X = F, Cl, Br, I). 

The opportunity of employing various electrophiles and functionalized diene precursors greatly enhances the synthetic potential of p3-allyltitanocenes. Besides aldehydes and ketones, carbon dioxide [11,15,16], acid chlorides [17], imines [11], nitriles [11], isocyanides [11], and organotin halides [18] react to afford the corresponding allylated products after hydrolysis. Examples are given in Scheme 13.8. 

Organotin halides are commonly prepared by the Kocheshkov redistribution reaction, where an organic group on tin (e.g., in SnR4) exchanges (reversibly) with a halide group on tin (e.g., in SnCLt).64 Two recent examples are shown in Equations (125) and (126). The first reaction exploits the high reactivity of the Sn-Me bonds, and the second... 

Conversion of the organotin chlorides into fluorides, bromides, or iodides is usually carried out with the sodium halide in acetone, and residual organotin compounds are often removed as the insoluble organotin fluorides. The fluorides can then be converted back into the bromides, chlorides, or iodides (and exchanges by other halides can be brought about with aqueous ammonium halides at room temperature).332 A 2 1 mixture (solid solution) of CsF and CsOH, mixed with silica gel, also provides a very convenient way of removing organotin halide byproducts from solution.333... 

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... 

Fig. 13.10 Chromatogram of hydrides generated from a known mixture of Sn(IV) and nine organotin halides... 

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. 

Reaction conditions Aqueous solutions of cotton (0.100 g 0.62 moles) with bisethylenediamine copper (II) hydroxide to give 25 ml solution are added to rapidly stirred (about 20,500 rpm no load) carbon tetrachloride (25 ml) solutions containing the organotin halide at about 25°C, 30 secs stirring time. 

A very versatile preparation seems to be the elimination of organotin halides in the reaction of organostannyl-organosilylcyclopentadienes with metal carbonyl halides. This reaction is very selective and only Sn—C bonds are cleaved with formation of 7)5-cyclopentadienyl complexes (7) ... 

Reaction of fluorinated alkenyl Grignard reagents or lithium reagents with organotin halides has been utilized for the preparation of fluorinated alkenyl tin reagents [111, 182-184]. Recently, a novel, general and convenient method has been developed for the preparation of a variety of fluorinated alkenylstannanes... 

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