Nickel(II) complexes with tetra- and pentadentate aminopyridine ligands: synthesis, structure, electrochemistry, and reduction to nickel(I) species.
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.
Kryatov
Sergey V
SV
Department of Chemistry, Tufts University, Medford, Massachusetts 02155, USA.
Mohanraj
B Sharmila
BS
Tarasov
Vladislav V
VV
Kryatova
Olga P
OP
Rybak-Akimova
Elena V
EV
Nuthakki
Bharathi
B
Rusling
James F
JF
Staples
Richard J
RJ
Nazarenko
Alexander Y
AY
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
C453159:1,2-dibromocyclohexane; D000631:Aminopyridines; D003510:Cyclohexanes; D053138:Cyclohexenes; D008024:Ligands; D009942:Organometallic Compounds; C052568:cyclohexene; D009532:Nickel