Tetraorganotin

Physica.1 Properties. Physical properties of typical tetraorganotin compounds are shown in Table 3. AH tetraorganotin compounds are insoluble in water but are soluble in many organic solvents. 

Table 3. Physical Properties of Typical Tetraorganotin Compounds ...

Chemical Properties. The most impoitant reactions which tetraorganotins undergo are heterolytic, ie, electrophilic and nucleophilic, cleavage and Kocheshkov redistribution (81—84). The tin—carbon bond in tetraorganotins is easily cleaved by halogens, hydrogen hahdes, and mineral acids ... 

The most widely utilized reaction of tetraorganotins is the Kocheshkov redistribution reaction, by which the tri-, di-, and in some cases the monoorganotin hahdes can be readily prepared ... 

If the reaction temperature is controlled through the use of a low boiling solvent or other means, it is possible to isolate equimolar quantities of monoalkyl tin trichloride and tri alkyl tin chloride using a 1 1 ratio of tetraorganotin and tin tetrachloride ... 

When R is a lower alkyl, the organotin trichloride can be easily separated from the reaction mixture by extraction with dilute aqueous hydrochloric acid, in which it is soluble. This reaction also works well with unsymmetrical tetraorganotins and has been practiced commercially (85). 

Excess alkylating reagent is required if the tetraorganotin is desired as the exclusive product. In commercial practice, the stoichiometry is kept at or below 4 1, since the cmde product is usually redistributed to lower organotin chlorides in a subsequent step and an ether is used as the solvent (86). The use of diethyl ether in the Grignard reaction has been generally replaced with tetrahydrofuran. 

Organolithium and organosodium reagents can also be used to prepare tetraorganotins ... 

The Wurtz reaction, which reties on in situ formation of an active organosodium species, is also usefiil for preparing tetraorganotin compounds and is practiced commercially. Yields are usually only fair and a variety of by-products, including ditins, also form ... 

Unsymmetrical functional tetraorganotins are generally prepared by tin hydride addition (hydrostaimation) to functional unsaturated organic compounds (88) (see Hydroboration). The realization that organotin hydrides readily add to atiphatic carbon—carbon double and triple bonds forming tin—carbon bonds led to a synthetic method which does not rely on reactive organometatiic reagents for tin—carbon bond formation and, thus, allows the synthesis of... 

Uses. The main use for tetraorganotin compounds is as (usually captive) intermediates for the tri-, di-, and monoorganotins. Although there have been reports in the patent Hterature of the use of tetraorganotins as components of Ziegler-Natta-type catalysts for the polymeri2ation of olefins, there is no evidence that such catalysts ate used commercially. 

Prepa.ra.tlon, Triorganotin chlorides of the general formula R.SnX are the basic starting materials for other triorganotins. They are generally prepared by Kocheshkov redistribution from the cmde tetraorganotin ... 

Acid, hydrogen haUde, or halogen cleavage of tetraorganotins is not used except on a laboratory scale because they are wasteful of tin—carbon bonds and uneconomical on a commercial scale. 

Preparation ndMa.nufa.cture. Monoorganotin haHdes are the basic raw materials for all other triorganotin compounds and are generally prepared by Kocheshkov redistribution from the tetraorganotin, eg, tetrabutyltin or the higher organotin haHdes ... 

The toxicity of the tetraorganotins has beenUtde studied. Available Hterature indicates that tetrabutyltin and the higher tetraalkyltins are substantially less toxic than triorganotins to mammals if taken orally (175). The high toxicity reported for tetraethyltin (LD g = 9 16 mg/kg) appears to be caused by its rapid conversion in the Hver to a triethyl tin species. 

Organotin(rV) compounds are characterized by the presence of at least one covalent C-Sn bond. The compounds contain tetravalent Sn centers and are classified as mono-, di-, tri-, and tetraorganotin(IV), depending on the number of alkyl (R) or aryl (Ar) moieties bound. The anions are usually CP, F , 0 , OH , -COO , or -S . It seems that the nature of the anionic group has only secondary importance in biological activity. 

Kumar Das et al. obtained a unique hexacoordinated tetraorganotin compound, bis C,N-[3-(2-pyridyl)-2-thienyl] diphenyltin(IV). The crystal... 

The reactions of tetraorganotins with ICl, EBr, and CICN have been investigated as synthetic routes to aryl cyanides (111) and alkyltin bromides and chlorides (112,113). 

The tetraorganotin compounds, R4Sn, show no tendency to increase their coordination number, owing to their weak, Lewis acidity conferred by the four electron-releasing alkyl groups. It has, however, been claimed (353) that trimethyl(trifluoromethyl)tin forms a 1 1 adduct with hexamethylphosphoric triamide, and that this may be isolated in the solid state. 

The tetraorganotins, R4Sn, are used primarily as intermediates in the industrial synthesis of organotins from SnCU (see Section II), and have no large industrial application. 

In 1935, Naumov and Manulkin 7) tried without success to isolate (—)-methyl-ethylpropyltin iodide, (—)-(/). In fact, triorganotin halides are generally configurationally unstable, as shown in 1968 by Peddle and Redl8), whereas tetraorganotin compounds appeared to be configurationally stable within the NMR time-scale (see below). 

Compound (+ )-(53) has been made from one of the diastereomers of the (—)-menthyl ester of 3-(p-anisylmethyl-l-naphthylstannyl)propionic acid, (54) ([a]p°° — 24) which could be obtained from the mixture of diastereomers because it is much less soluble in -pentane at low temperature than the other one. Their separation could be followed by NMR, both diastereomers differing by the position of their methoxy signal. The pure less soluble diastereomer (54) reacts with methylmagnesium iodide to give a tetraorganotin compound containing only one chiral center, the asymmetric tin atom 36> 87>. 

Table 6. Room temperature partial chromatographic resolution of 75 mg tetraorganotin compounds on microcrystalline cellulose triacetate (column A)...

A trapping experiment of the optically active triorganotin chloride (5) with isopropylmagnesium bromide did give the expected methylneophylphenylisopropyltin (9) in a 20% yield but unfortunately, this tetraorganotin compound, which is optically stable (see Table 1), was obtained as a racemic mixture. 

From Tetraorganotins to Triorganostanny 1-Transition Metal Complexes... 

Figure 42 shows spectra of the simplest tetraorganotin compound, tetramethyltin. The upper spectrum was recorded with complete decoupling of all protons, the middle spectrum without. The result is a multiplet with 13 lines (n = 12), but if you work out the binomial coefficients for such a multiplet you will see that the outer two lines are too weak to be seen. The lower spectrum is the proton spectrum, which shows satellites due to two-bond tin-proton coupling to the tin-117 (inner lines) and tin-119 (outer lines) nuclei. 

Triorganotin Bromide. Tetraorganotin compounds were brominated with stoichiometric quantities of bromine (2 moles of bromine for each mole of tetraorganotin). Bromination was carried out after cooling the tetraorganotin compound in a dry ice-acetone bath. The contents then were slowly brought to room temperature. In most cases, the crude bromides were used as such for fluorination. 

Synthesis and Characterization. Tris(trimethylsilylpropyl)tin fluoride (PTF) and tris(trimethylsilylmethyl)tin fluoride (MTF) were synthesized according to scheme A (Figure 1) while scheme B (Figure 1) was followed in the synthesis of dibutyl-(trimethylsilylpropyl)tin fluoride (BTF). MTF has been reported in the literature (6) however, it was synthesized to compare its solution properties with the other two novel compounds. The steps involved in these syntheses were straight-forward and thus need no elaboration. In the synthesis of BTF, the unsymmetrical triorganotin fluoride, bromination of tetraorganotin compound resulted... 

---