A Structure-Activity Study of Nickel NNN Pincer Complexes for Alkyl-Alkyl Kumada and Suzuki-Miyaura Coupling Reactions

A new series of Ni NNN pincer complexes were synthesized and characterized. The main difference among these complexes is the substituents on the side arm amino group(s). No major structural difference was found except for the C-N-C angle of the various substituents and the 'pseudo bite angle' of the complexes. Four new complexes were efficient for the alkyl-alkyl Kumada reaction of primary alkyl halides, and among them, one complex was also efficient with secondary alkyl halides. The influence of the substituents on the catalytic performance of the Ni complexes in alkyl-alkyl Kumada and Suzuki-Miyaura cross-coupling reactions was systematically investigated. No correlation was found between the catalytic activity and the key structural parameters (C-N-C angle and 'pseudo bite angle'), redox properties or Lewis acidity of the complexes.