title: On Ni catalysts for catalytic, asymmetric Ni/Cr-mediated coupling reactions.
abstract: The importance of the Ni catalyst in achieving catalytic asymmetric Ni/Cr-mediated coupling reactions effectively is demonstrated. Six phenanthroline-NiCl(2) complexes 1a-c and 2a-c and five types of alkenyl iodides A-E were chosen for the study, thereby demonstrating that these Ni catalysts display a wide range of overall reactivity profiles in terms of the degree of asymmetric induction, geometrical isomerization, and coupling rate. For three types of alkenyl iodides A-C, a satisfactory Ni catalyst(s) was found within 1a-c and 2a-c. For disubstituted (Z)-alkenyl iodide D, 2c was identified as an acceptable Ni catalyst in terms of the absence of Z → E isomerization and the degree of asymmetric induction but not in terms of the coupling rate. Two phosphine-based Ni catalysts, [(Me)(3)P](2)·NiCl(2) and [(cy)(3)P](2)·NiCl(2), were found to meet all three criteria for D. The bond-forming reaction at the C16-C17 position of palytoxin was used to demonstrate the usefulness of the Ni catalysts thus identified.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Xiang
authors.initials: X
authors.lastname: Liu
authors.forename: Xiaoyong
authors.initials: X
authors.lastname: Li
authors.forename: Yu
authors.initials: Y
authors.lastname: Chen
authors.forename: Yimin
authors.initials: Y
authors.lastname: Hu
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Kishi