Preparation and Reactions of Organotin Compounds

The synthesis and properties of the tin-carbon bond were reviewed in reference (35). Three recent volumes of Gmelin, written by H. Schumann and I. Schumann, comprehensively cover the literature, up to the end of 1973, on tetraalkyltin compounds R4Sn (36), RaSnR (37), and RsSnRj, RjSnR R , and RR SnR R 38), and are invaluable sources of reference. 

Four principal methods have been developed for forming a bond between tin and carbon. 

Advances since 1970 have been made in the improvement and exten- 

The direct synthesis (39) has obvious attractions as an industrial process, hut, in the absence of a catalyst, it proceeds readily only for allyl and benzyl halides, and much attention has been directed towards finding suitable promoters for the reactions. 

One approach (40) has been to conduct the reaction in the presence of a more electropositive metal, often as an alloy. In the presence of magnesium, tin reacts with ethyl bromide to give tetraethyltin, and various additives promote the reaction, the sequence of effectiveness being carbitols I tetrahydrofuran, tetrahydrothiophene ether triethylamine Br the ions ClOj, PF, BF, and BPh are without effect. It is suggested that this reflects the coordination of the additive (L) to the Grignard reagent that is first formed, making it more reactive towards metallic tin. 

---

A.G. Davies (2004) Organotin Chemistry, 2nd edn, WUey-VCH, Weinheim - This book includes an up-to-date coverage of the preparation and reactions of organotin compounds. 

S2fi) Sisido, K., Kozima, S., Takizawa, K. Optically active organotin compounds. Preparation and reaction of (l-Methyl-2,2-diphenyl-cyclopropyl)trimethytin. Tetrahedron Letters 1967, 33. - Gas Chromatog. Abstr. 1967, 1112. 

The majority of the more important methods for the preparation of fluorinated compounds by substitution reactions have been reviewed in the previous sections. There are, however, some additional important synthetic procedures which should also be mentioned, mainly those concerned with the introduction of fluorine by substitution of functional groups containing boron, silicon and tin the reactions of organotin compounds are the most well-studied to date. These reactions are excellent synthetic methods for obtaining vinyl and aryl fluorides (sec also Section 1.1.1.1.). 

Reactions of organotin compounds with Lewis acids by have been carried out particularly with mercury(II) salts in mechanistic studies, with SnCl4 (the Kocheshkov reaction) for the preparation of alkyltin chlorides, and with lead tetraacetate. 

B. Preparation and Properties of Organotin Hydrides II. Reactions with Organic Compounds. 

Synthetic and mechanistic aspects of the reactions of the alkali-metal derivatives of organotin compounds, RaSnM ("organostannylan-ionoids ) have been reviewed (79, 80). They may be prepared by reactions of the types shown in the following equations. 

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). 

The Stille protocol is now well established, and finds many uses in preparative chemistry. Especially, application to the synthesis of bioactive substances and functional materials is noteworthy. The choice of catalyst and solvent, however, is still remained veiled. If the reaction to be attempted is not well documented, one should first try to find the most suitable reaction conditions. Organotin compounds can be extremely toxic, and tributyltin compounds are recently suspected to be endocrine disrupters. The presence of even traces of organotin contaminants in organic products must be avoided, as far as possible. In spite of these problems, the Stille protocol will continue to be a favorite method for car-bon-carbon-bond formation, owing to the mildness of the reaction conditions and the functional tolerability of both substrates and reagents. 

---