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 : (BuZnBr)-Bu-n, suggesting that a higher-order zincate, presumably LimZn(Bu-n)Br-3((2-m)-), is the active transmetalating agent.