Palladium catalysis homocoupling

Besides such homocoupling of alkynes, adduct (58) may be heterocoupled, under palladium catalysis, with a vinylic bromide that itself may have been formed by the hydroalumination of a different alkyne (equations 65 and 66). ... 

Itami went on to report a new synthesis of [12JCPP based on the shotgun homocoupling of dihalide 56 with bis(cyclooctadiene)nickel(0) in the presence of 2,2 -bipyridyl. This new approach circumvented the synthesis of a boronate and also the need for palladium catalysis, albeit stoichiometric nickel is required (Fig. 27). With these synthetic advantages, Itami was able to synthesize 61, the macrocyclic precursor to [12JCPP on a gram scale. In addition, the authors report that with this synthesis they were able to produce 0.5 g in total of [12JCPP from combined reaction products [36]. 

There has been a review of palladium-catalysed carbonylative coupling reactions of aryl halides with carbon nucleophiles in the presence of carbon monoxide. It has been shown that rhodium is an efficient catalyst for the homocoupling reaction of arylzinc compounds in the presence of 1 atm of carbon monoxide to give diaryl ketones. Under similar conditions, palladium and nickel catalysts yield biaryls. The beneficial catalysis by rhodium is likely to derive from the ease of migration of the aryl ligand to carbon monoxide in the rhodium(III) intermediate. A rhodium catalyst has also been used in the formation of indole-3-carboxylates by reaction of indoles with alcohols in the presence of carbon monoxide. The catalytic cycle. Scheme 5, is likely to involve metallation of the indole at the 3-position, followed... 

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