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

TL;DR

This paper describes the synthesis and evaluation of new nickel-based glycine equivalents with improved reactivity for chemical substitutions.

Contribution

A new nucleophilic glycine equivalent with a chlorine atom for enolate stabilization is introduced.

Findings

The new complexes show reactivity comparable to more complex trifluoromethyl-stabilized complexes.

Competitive benzylation and bis-propargylation reactions were used to evaluate hydrogen substitution.

Phase transfer conditions with potassium hydroxide were effective for the alkylation process.

Abstract

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.

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