Halostannanes reactions

Another major route for synthesis of stannanes is reaction of an organometallic reagent with a trisubstituted halostannane, which is the normal route for the preparation of aryl stannanes. 

The halostannanes can also be generated in situ by reactions of allylic halides with tin metal or stannous halides. 

Reactions of tetraallylstannanes with aldehydes catalyzed by SnCl4 also appear to involve a halostannane intermediate. It can be demonstrated by NMR that there is a rapid redistribution of the allyl group.174 Reactions with these halostannanes are believed to proceed through a cyclic TS. 

Various allylhalostannanes can transfer allyl groups to carbonyl compounds. In this case, the reagent acts both as a Lewis acid and as the source of the nucleophilic allyl group. Reactions with halostannanes are believed to proceed through cyclic transition states. 

When Lewis acids such as SnCU and TiCU are used to promote additions of allylic trialkyltin reagents to aldehydes several reaction outcomes are possible, depending on stoichiometry and the mode of addition. If the Lewis acid is added to the aldehyde followed by the allylic stannane, the typical product (syn for crotylstannanes) derived from an acyclic transition state is formed. If, however, the stannane and Lewis acid are premixed and left to equilibrate, metathesis can occur forming the allylic halome-tal compound which reacts with the subsequently added aldehyde to give products (anti for crotyl) consistent with a cyclic transition state (Eq. 22). The initially formed allylic halostannane gives rise to the linear adduct, but if aldehyde addition is delayed, this initial secondary allylic metal halide can equilibrate to the primary isomer which then reacts with the aldehyde to afford the branched product. 

Reactions of halostannanes with complex hydrides provide routes to stannanes (Table 1). Complex hydrides most used are MBH. (M = Li, Na, K) and LiAlH. The LiBH and LiAlH, reductions are carried out in aprotic ether solvents (THE, EtjO, monoglyme). Sodium and K hydroborate reactions may be carried out in H O. Most complex hydride reductions are adaptable to Sn — D bond synthesis (see also 1.6.7.1.4). Halostannanes are reduced by LiAlH ... 

Various organotin compounds with tin-heteroatom bonds are synthesized by the reactions of halostannanes with the corresponding heteroatom nucleophiles. For example, trialkyltin alkoxides and trialkyltin amides are prepared by the treatments of halostannanes with sodium alkoxides (eq (139)) [134] and lithium amides (eq (140)) [135], respectively. Tin alkoxides are also formed by the reaction of alcohols with tin amides (eq (141)) [136]. 

A Bm-containing molybdenum stannyl complex has been synthesized by oxidative addition of [Me2Sn(Bm)]Cl to Mo(0) precursors (Fig. 5.14) or through reactions of halostannanes with Na[Mo-(CO)3(Bm)]. The crystal structure of [Mo(CO)3(SnMe2Cl)(Bm)] in which Bm bridges both molybdenum and tin centers is also reported.26... 

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