Silver Grignard reagent coupling

Coupling to produce dimeric product was a side reaction in these systems also, e.g. 75 % dimer formation was reported for poly(styryl)lithium and 23 % dimer formation with the poly(styryl)-Grignard reagent 326). However, it should be noted that the only reported characterizations of these reactions were size exclusion chromatography traces and silver catalyzed polymerization of tetrahydrofuran using the polymeric halogen compounds as co-initiator. 

Tamura and Kochi studied the cross-coupling reactions of alkyl halides with alkyl Grignard reagents catalyzed by silver compounds first [422, 426, 427]. The coupling of primary alkyl halides with primary Grignard reagents resulted in a mixture... 

D. Homo-Coupling with Silver(I). Silver is an effective catalyst for the coupling of Grignard reagents and alkyl halides, and it is especially useful when both alkyl groups are the same.(43) When different alkyl groups are employed, a mixture of three coupled products is obtained. Disproportionation becomes increasingly important with secondary and tertiary... 

The rate of reaction shows first order dependence on the concentration of iron and ethyl bromide, but is independent of the concentration of ethylmagnesium bromide. The rate, however, varies with the structure of the Grignard reagent, and disproportionation usually results except when the alkyl group is methyl, neopentyl or benzyl which possess no g-hydrogens. The reactivities of the alkyl bromides (t-butyl >i-propyl >n-propyl) as well as the kinetics are the same as the silver-catalyzed coupling described above and suggest a similar mechanism ... 

Silver is also an effective catalyst for the coupling of Grignard reagents and alkyl halides, but is useful only when both alkyl groups are the same ... 

Grignard reagents also react with inorganic halides to give coupled products. Examples of such halides are cupric chloride, lead chloride, silver bromide, silver cyanide, nickel chloride, palladium chloride, chromic chloride, iron halide, ruthenium halide, and rhodium halide. 

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