Bond cleavage carbon-tin

Isotopic labelling, Eq. (49), indicated that the transmetalation occurs via direct tin-carbon bond cleavage rather than via intermediate formation of an alkoxy-cyclopropane [45],... 

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 ... 

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. 

Heterolytic cleavage of the tin-carbon bond is reviewed in references (94-96). Cleavage by electrophiles (e.g, HgXj or halogen) is dominated by electrophilic attack at carbon, and cleavage by nucleophiles principally involves nucleophilic attack at tin. Much of the interest in these processes centers on the intermediate mechanisms that may exist between these extremes, in which electrophilic attack is accompanied by some nucleophilic assistance, and vice versa. Allylic, al-lenic, and propargylic compoimds show a special reactivity by a special (Se2 or SE2y) mechanism. 

Cleavage of the tin-carbon bond can also be achieved by bimolecu-lar, homolytic substitution (Sh2) at the tin center (130-132). 

Stannoles are more easily cleaved by acids than are siloles. At room temperature, brief exposure of 1,1-dimethyltetraphenylstannole to a dilute solution of acetic acid in alcohol resulted in rapid cleavage of the two tin-carbon bonds, affording (E,E)-, 2,3,4-tetraphenylbutadiene. 

In the stannole series, the reactions could be explained by the extraordinary reactivity of the exocyclic tin-carbon bonds with regard to lithium reagents. Thus, the reaction of 1,4-dilithio-1,2,3,4-tetraphenyl-1,3-butadiene with 1,1 -dialkyl-2,3,4,5-tetraphenylstannole leads to alkyl-tin bond cleavage-cyclization by the dilithium reagent33 (equation 61). 

Homolytic cleavage of a tin carbon bond in a tetraorgan-otin compound is less frequently encountered than is heterolytic cleavage. Such radicals as Bn, , and the suc-cinimidyl radical can take part in Sn2 displacement with tetraorganotins (Scheme 8). The reactivity of ITiSn in MezCO towards the succinimidyl radical is in the sequence of R = Me > Et > Pr > Bn this is the reverse of that for radical reactions of iodine and bromine. 

In heterolytic cleavages of tin carbon bonds, electrophilic attack (by E) at carbon is usually the more influential, although nucleophilic assistance (by Nu) at tin can also play a role, and in some cases can become dominant (equation 37). 

H. Matsuda Kagaku [Kyoto) 26, 137 (1971) Formation and cleavage of tin-carbon bonds 4... 

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