Interaction of amino bases with tartrate-modified Ni catalysts

After poisoning with pyridine, tartaric acid-modified Ni catalysts showed an unexpected behavior as regards the dependence of enantioselectivity on the reaction temperature. While in the absence of a poison the enantioselectivity decreased with increasing reaction temperature, it remained constant for pyridine-poisoned Ni catalysts. This phenomenon is tentatively explained by assuming that ligand water is replaced by pyridine ligands in the Ni-tartrate complexes on the nickel surface. As pyridine is strongly held by Ni²⁺ ions, a higher ligand rigidity is attained which keeps the selectivity of the catalyst constant.