A Straightforward Electrochemical Approach to Imine- and Amine-bisphenolate Metal Complexes with Facile Control Over Metal Oxidation State.

Michael R Chapman,Bao N Nguyen,Charlotte E Willans,Nikil Kapur,Susan E Henkelis

doi:10.1002/open.201600019

Abstract

Synthetic methods to prepare organometallic and coordination compounds such as Schiff‐base complexes are diverse, with the route chosen being dependent upon many factors such as metal–ligand combination and metal oxidation state. In this work we have shown that electrochemical methodology can be employed to synthesize a variety of metal–salen/salan complexes which comprise diverse metal–ligand combinations and oxidation states. Broad application has been demonstrated through the preparation of 34 complexes under mild and ambient conditions. Unprecedented control over metal oxidation state (MII/III/IV where M=Fe, Mn) is presented by simple modification of reaction conditions. Along this route, a general protocol‐switch is described which allows access to analytically pure FeII/III–salen complexes. Tuning electrochemical potential, selective metalation of a Mn/Ni alloy is also presented which exclusively delivers MnII/IV–salen complexes in high yield.

Highlights

Schiff-base ligands are amongst the most widely studied chelators in inorganic chemistry, with salen-type ligands forming a popular class of Schiff-bases
Salen-type ligands in particular have been coordinated to a broad range of metal centers and have been used widely in catalysis, in addition to biomedical and materials applications.[1,2,3,4,5,6,7,8]
A common method to prepare metal–salens involves reaction of the ligand with metal acetate, with high temperatures often being necessary (e.g., Fe and Mn) and column chromatography being required for purification (e.g., Cu), often resulting in low yields.[9]

Summary

Introduction

Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under http://dx.doi.org/10.1002/ open.201600019. Oxidation of the sacrificial copper anode occurs, liberating Cu+ ions into solution These two species combine to deliver the desired CuIÀNHC complex. To complement these findings and extend the current state-of-the-art,[18,19,20,21,22,23,24,25] it was hypothesized that any HL ligand with an appropriate reduction potential could be used with a range of metals to electrochemically prepare organometallic complexes in a simple and economical manner. Electrochemical synthesis of metal–ligand complexes: a) reduction of HL ligand; b) oxidation of metal; c) combination of ligand and metal

Results and Discussion

Conclusion

Experimental Section

General procedure for FeII and MnII complexes