Synthesis and characterization of aluminum nitroxide complexes

• Published in: Polyhedron 2016-08, Vol.114 (C), p.194-199
• Main Authors: Herb, Thomas M., Poitras, Andrew M., Richardson, Kenneth G., Cole, Bren E., Bogart, Justin A., Carroll, Patrick J., Schelter, Eric J., Graves, Christopher R.
• Format: Article
• Language: English
• Subjects: Aluminum; Electrochemistry; Nitroxide ligand; Non-innocent ligand; Redox-active ligand
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2015.12.005

Aluminum complexes of pyridyl nitroxide ligands have been prepared and characterized spectroscopically and structurally. Electrochemical analysis of the complexes shows multi-electron redox properties of the complexes with redox potentials dependent on the ligand substitution pattern. [Display omitted] We report the synthesis of aluminum complexes of pyridyl nitroxide (RpyNO−) ligands. The dimeric complexes {(μ-pyNO−)Al(CH3)2}2 (1) and {(μ-CH3pyNO−)Al(CH3)2}2 (2) were prepared through the 1:1 reaction between the pyridyl hydroxylamine ligand precursors RpyNOH and trimethylaluminum. Both compounds were characterized by 1H and 13C NMR spectroscopies. X-ray structural analysis revealed that 1 and 2 are isostructural, with the dimer structure resulting from an Al2O2 core. Reaction of pyNOH with two equivalents of trimethylaluminum yielded the aluminum complex (pyNO−)AlMe2·AlMe3 (3), which was also characterized by 1H and 13C NMR spectroscopies and single-molecule X-ray diffraction. The electronic structure of the {(μ-pyNO−)Al(CH3)2}2 and {(μ-CH3pyNO−)Al(CH3)2}2 complexes were interrogated using UV–Vis electronic absorption spectroscopy and electrochemistry. The cyclic voltammograms of the complexes show two separate oxidation processes, the potentials of which are both dependent on the substitution pattern of the RpyNO− ligands.