Hydrostannation and Dimetallation

Hydrometallation proceeds by proximal bond cleavage. Addition of HSnBus affords the homoallylstaimane 172 [56]. The addition may be understood formally by the formation of the palladacycle 171, but explanation by the formation of the cyclo-propylcarbinylpalladium 173 is more appropriate. The intermediate 173 undergoes i6-carbon elimination to generate the homoallylpalladium 174, which then gives rise to 172 by reductive elimination. Addition of HSnBus to a substituted MCP 175 to yield 176 can be understood by this mechanism. 

Dimetallation may be understood by participation of both palladacycles 167 and 168. In general, addition of dimetallic reagents occurs via the palladacycles 177 with cleavage of the proximal bond to provide 178. For example, borylsilylation of the MCP 179 with 180 gave 181 using a combination of Pd(OAc)2 with r-octyl isocyanide (XVII-6). On the other hand, addition via the distal bond cleavage was observed in the reaction of the same reagent 180 with the MCP 182, and the product 183 was obtained via 184 [57]. 

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