Synthesis and Evaluation of a Series of Ni(II) Complexed Nucleophilic Glycine Equivalents

The synthesis of a series of Ni-(II) complexed glycine Schiff bases as well as the appropriate precursors is described. Included in this series is a new nucleophilic glycine equivalent, which includes an electron withdrawing chlorine atom which stabilizes the extended enolate necessary for alkylation of the glycine Schiff base. Additionally, the reactivity of this system was evaluated and compared to previous iterations of these complexes for the substitution of one or both protons of the glycine methylene moiety. The substitution of the first hydrogen was evaluated through a series of competitive benzylation reactions with benzyl bromide under phase transfer conditions with aqueous potassium hydroxide as the base. The substitution of both hydrogen atoms from the glycine moiety was evaluated by a similar process through bis-propargylation of the methylene group. It was found that this new series of complexes is similar in reactivity to the more synthetically complicated complexes, which incorporate a trifluoromethyl group for stabilization.