On the role of additives in alkyl–alkyl Negishi cross-couplings

An additives study for the alkyl–alkyl Negishi reaction using an NHC–Pd catalyst revealed that bromide salts promote coupling while the cation is mechanistically benign. A double titration revealed that the cross-coupling begins at a 1 ∶ 1 ratio of LiBr ∶ nBuZnBr, suggesting that a higher-order zincate, presumably LimZn(nBu)Br3(2−m)−, is the active transmetalating agent.