title: Synthesis and Characterization of Aluminum Complexes of Redox-Active Pyridyl Nitroxide Ligands.
abstract: The aluminum complexes ((R)pyNO(-))2AlCl ((R)pyNO(-) = N-tert-butyl-N-(2-pyridyl)nitroxyl; R = H (1), CH3 (2), CF3 (3)) were prepared in 80-98% yield through the protonolysis reaction between the pyridyl hydroxylamine ligand precursors (R)pyNOH and dimethylaluminum chloride. Complex 1 was also prepared using a salt metathesis route in 92% yield. Complexes 1-3 were characterized using (1)H and (13)C NMR spectroscopies. Single-crystal X-ray diffraction analysis of the complexes revealed that 1-3 are isostructural, with the Al(III) cation in all cases being five coordinate with distorted square pyramidal geometries. The geometry of complex 1 was studied using DFT, which showed primarily ligand-based frontier molecular orbitals. Reaction of 1 with NaOt-Bu gave (pyNO(-))2AlOt-Bu (4), while reaction of 1 with AgBPh4 gave [(pyNO(-))2Al(THF)2][BPh4] (5) in 54% and 87% yields, respectively. Compounds 4 and 5 were both characterized using (1)H and (13)C NMR spectroscopies and compound 5 by X-ray diffraction. Complexes 1-5 were also characterized by UV-vis electronic absorption spectroscopy and electrochemistry. The cyclic voltammograms of the complexes show two separate oxidation process, the potentials of which are dependent on both the substitution pattern of the (R)pyNO(-) ligands and the anion that completes the aluminum coordination sphere. A correlation was determined between the chemical shift of the t-Bu of the (R)pyNO(-) ligand in the (1)H NMR spectroscopy and the potentials of the redox events for complexes 1-4.
authors.affiliation: Department of Chemistry & Biochemistry, Albright College , 13th & Bern Streets, Reading, Pennsylvania 19612, United States.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Poitras
authors.affiliation: P. Roy, Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , 231 South 34th Street, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Justin A
authors.initials: JA
authors.lastname: Bogart
authors.affiliation: P. Roy, Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , 231 South 34th Street, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Bren E
authors.initials: BE
authors.lastname: Cole
authors.affiliation: P. Roy, Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , 231 South 34th Street, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Carroll
authors.affiliation: P. Roy, Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , 231 South 34th Street, Philadelphia, Pennsylvania 19104, United States.
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Schelter
authors.affiliation: Department of Chemistry & Biochemistry, Albright College , 13th & Bern Streets, Reading, Pennsylvania 19612, United States.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Graves