Identification of a Higher-Order Organozincate Intermediate Involved in Negishi Cross-Coupling Reactions by Mass Spectrometry and NMR Spectroscopy

Negishi cross-coupling reactions were analyzed in solution by mass spectrometry and NMR spectroscopy to identify both the effect of LiBr as an additive as well as the purpose of 3-dimethyl-2-imidazolidinone (DMI) as a co-solvent. The results suggest that the main role of DMI is to facilitate a higher order bromo-zincate formation during the addition of LiBr.