title: Nickel(II) complexes with tetra- and pentadentate aminopyridine ligands: synthesis, structure, electrochemistry, and reduction to nickel(I) species.
abstract: A series of nickel(II) complexes with polydentate aminopyridine ligands N,N,N'-tris-[2-(2'-pyridyl)ethyl]ethane-1,2-diamine (L1), N,N,N'-tris-[2-(2'-pyridyl)ethyl]-N'-methylethane-1,2-diamine (L2), and N,N'-bis-[2-(2'-pyridyl)ethyl]-N,N'-dimethylethane-1,2-diamine (L3) were synthesized and characterized by elemental analysis and spectroscopic methods. Single-crystal X-ray diffraction studies showed that the Ni(II) ions have five-coordinate square-pyramidal geometry in [NiL2](ClO(4))(2), similar to that previously found in [NiL1](ClO(4))(2) x CH(3)NO(2) (Hoskins, B. F.; Whillans, F. D.J. Chem. Soc., Dalton Trans. 1975, 657), and square-planar geometry in [NiL3](ClO(4))(2). All three nickel(II) complexes are reduced by sodium borohydride or sodium amalgam in organic solvents to nickel(I) species, which were identified by highly anisotropic EPR spectra at 100 K: g(1) = 2.239, g(2) = 2.199, and g(3) = 2.025 for [NiL1](+); g(axially) = 2.324 and g(radially) = 2.079 for [NiL2](+) and [NiL3](+). Cyclic voltammetry of the nickel(II) complexes in acetonitrile exhibited reversible reduction waves at -1.01 V for [NiL1](2+), -0.91 V for [NiL2](2+), and -0.83 V for [NiL3](2+) versus SCE, potentials which are significantly less negative than those of most previously characterized Ni(II) complexes with nitrogen-only donor atoms. Complexes [NiL1](2+) and [NiL2](2+) showed high catalytic activity in the electroreduction of 1,2-trans-dibromocyclohexane to cyclohexene.
authors.affiliation: Department of Chemistry, Tufts University, Medford, Massachusetts 02155, USA.
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Kryatov
authors.forename: B Sharmila
authors.initials: BS
authors.lastname: Mohanraj
authors.forename: Vladislav V
authors.initials: VV
authors.lastname: Tarasov
authors.forename: Olga P
authors.initials: OP
authors.lastname: Kryatova
authors.forename: Elena V
authors.initials: EV
authors.lastname: Rybak-Akimova
authors.forename: Bharathi
authors.initials: B
authors.lastname: Nuthakki
authors.forename: James F
authors.initials: JF
authors.lastname: Rusling
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Staples
authors.forename: Alexander Y
authors.initials: AY
authors.lastname: Nazarenko
mesh_terms: D000631:Aminopyridines / Q000737:chemistry*; D002384:Catalysis; D003510:Cyclohexanes / Q000737:chemistry; D053138:Cyclohexenes; D004563:Electrochemistry; D004572:Electrolysis; D004578:Electron Spin Resonance Spectroscopy; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D010084:Oxidation-Reduction; D013237:Stereoisomerism; D014961:X-Ray Diffraction
chemical_list: C453159:1,2-dibromocyclohexane; D000631:Aminopyridines; D003510:Cyclohexanes; D053138:Cyclohexenes; D008024:Ligands; D009942:Organometallic Compounds; C052568:cyclohexene; D009532:Nickel