Synthesis and characterization of aluminum nitroxide complexes

We report the synthesis of aluminum complexes of pyridyl nitroxide ((R)pyNO(-)) ligands. The dimeric complexes {(mu-pyNO(-))Al(CH3)(2)}(2) (1) and {(mu-(CH3)pyNO(-))Al(CH3)(2)}(2) (2) were prepared through the 1:1 reaction between the pyridyl hydroxylamine ligand precursors (R)pyNOH and trimethylaluminum. Both compounds were characterized by H-1 and C-13 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 center dot AlMe3 (3), which was also characterized by H-1 and C-13 NMR spectroscopies and single-molecule X-ray diffraction. The electronic structure of the {(mu-pyNO(-))Al(CH3)(2)}(2) and {(mu-(CH3)pyNO(-))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 (R)pyNO(-) ligands. (C) 2015 Elsevier Ltd. All rights reserved.