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The electrochemical generation and reactions of some square planar nickel complexes

The electrochemical generation and reactions of some square planar nickel complexes
The electrochemical generation and reactions of some square planar nickel complexes

The electrochemical reduction of a series of macrocyclic square planar nickel (II) complexes of Schiff base ligands has been studied in aprotic solvents. It is shown that the products of these reductions are the corresponding nickel (I) complexes which are stable in the absence of electrophiles. The reduced complexes, however, react with many primary, secondary, and tertiary alkyl bromides in a reaction which leads to a free alkyl radical and regeneration of the nickel (II) complex. Hence it is possible to reduce high concentrations of alkyl bromides in the presence of only a trace of complex and at the reduction potential of the nickel (II) species; this potential can be much less negative (i.e. 1 V) than that for the direct reduction of alkyl bromide. The reaction also has the advantage that the alkyl radical is formed away from the electrode and does not react with the metal of the electrode. The reduction potentials and reactivities are compared with those from similar experiments with cyclic amine complexes and some cobalt (II) Schiff base complexes. It is shown that the products of the reaction of metal (I) with the alkyl bromide are not always the same but evidence is presented that, in all cases the reaction of the metal (I) complex with alkyl halide proceeds via a metalcarbon bond and it is the lifetime of this bond which determines the chemistry observed. The possibilities for the design of catalysts for the selective reduction of alkyl bromides to radical or carbanion intermediates, or to allow the insertion of olefins into the metal-carbon bond is discussed.

University of Southampton
Gosden, Cary
Gosden, Cary

Gosden, Cary (1978) The electrochemical generation and reactions of some square planar nickel complexes. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The electrochemical reduction of a series of macrocyclic square planar nickel (II) complexes of Schiff base ligands has been studied in aprotic solvents. It is shown that the products of these reductions are the corresponding nickel (I) complexes which are stable in the absence of electrophiles. The reduced complexes, however, react with many primary, secondary, and tertiary alkyl bromides in a reaction which leads to a free alkyl radical and regeneration of the nickel (II) complex. Hence it is possible to reduce high concentrations of alkyl bromides in the presence of only a trace of complex and at the reduction potential of the nickel (II) species; this potential can be much less negative (i.e. 1 V) than that for the direct reduction of alkyl bromide. The reaction also has the advantage that the alkyl radical is formed away from the electrode and does not react with the metal of the electrode. The reduction potentials and reactivities are compared with those from similar experiments with cyclic amine complexes and some cobalt (II) Schiff base complexes. It is shown that the products of the reaction of metal (I) with the alkyl bromide are not always the same but evidence is presented that, in all cases the reaction of the metal (I) complex with alkyl halide proceeds via a metalcarbon bond and it is the lifetime of this bond which determines the chemistry observed. The possibilities for the design of catalysts for the selective reduction of alkyl bromides to radical or carbanion intermediates, or to allow the insertion of olefins into the metal-carbon bond is discussed.

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Published date: 1978

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Local EPrints ID: 460200
URI: http://eprints.soton.ac.uk/id/eprint/460200
PURE UUID: 6b051f51-fc53-4f11-ae40-b2c547ceb9dd

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Date deposited: 04 Jul 2022 18:10
Last modified: 04 Jul 2022 18:10

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Author: Cary Gosden

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