316381-49-4Relevant articles and documents
Synthesis and superoxide dismutase activity of novel iron complexes
Tamura, Masakazu,Urano, Yasuteru,Kikuchi, Kazuya,Higuchi, Tsunehiko,Hirobe, Masaaki,Nagano, Tetsuo
, p. 586 - 592 (2000)
We have previously shown that the Fe(II) tetrakis-N,N,N′,N′-(2-pyridylmethyl)ethylenediamine complex (Fe(II)TPEN) has high superoxide dismutase (SOD) activity, using the xanthine-xanthine oxidase-cytochrome c method (cyt. c method) [J. Biol. Chem. 264 (1989) 9243-9249]. X-ray analysis showed that Fe(II)TPEN has two different coordination structures, one in which Fe(II) is coordinated with six nitrogens of TPEN and one in which Fe(II) is coordinated with five nitrogens of TPEN and one oxygen of sulfate anion as the counter anion [Chem. Pharm. Bull. 48 (2000) 223-230]. To investigate the relationship between these two structures and SOD activity, we synthesized novel Fe(II) complexes of TPEN analogues and measured their SOD activity by the cyt. c method. The Fe(II) tetrakis-N,N,N′,N′-(2-pyridylmethyl)trimethylenediamine complex (Fe(II)TPTN) and the Fe(II) tris(2-pyridylmethyi)triazacyclononane complex (Fe(II)TPTCN) had no SOD activity (IC50 = > 100 μM), probably because these two complexes have undistorted steric structure with no easily substituted ligand. On the other hand, other Fe(II) complexes with unsaturated coordination or an easily substituted ligand had high SOD activity (IC50 = 0.4-20 μM). The results indicate that the substitution reaction of a ligand with superoxide or the coordination of superoxide is essential for Fe(II)TPEN analogue complexes to have SOD activity. Moreover, we examined the effect of steric hindrance of the ligands on the SOD activity and the stability of the iron complexes to oxygen.
A Mechanistic Study on the Reaction of Non-Heme Diiron(III)-Peroxido Complexes with Benzoyl Chloride
Lerch, Markus,Achazi, Andreas J.,Mollenhauer, Doreen,Becker, Jonathan,Schindler, Siegfried
, p. 4122 - 4132 (2021/09/30)
Dinuclear iron peroxido complexes are important intermediates for selective oxidation reactions. A detailed kinetic study of the reaction of benzoyl chloride (BzCl) with a dinuclear iron non-heme cis end-on peroxido complex with the ligand EtHPTB (N,N,N′,
Nickel(II) complexes of pentadentate N5 ligands as catalysts for alkane hydroxylation by using m-CPBA as oxidant: A combined experimental and computational study
Sankaralingam, Muniyandi,Balamurugan, Mani,Palaniandavar, Mallayan,Vadivelu, Prabha,Suresh, Cherumuttathu H.
, p. 11346 - 11361 (2015/02/02)
A new family of nickel(II) complexes of the type [Ni(L)(CH 3CN)](BPh4)2, where L=N-methyl-N,N′, N′-tris(pyrid-2-ylmethyl)-ethylenediamine (L1, 1), N-benzyl-N,N′, N′-tris(pyrid-2-yl-methyl)-ethylenediamine (L2, 2), N-methyl-N,N′- bis(pyrid-2-ylmethyl)-N′-(6-methyl-pyrid-2-yl-methyl)-ethylenediamine (L3, 3), N-methyl-N,N′-bis(pyrid-2-ylmethyl)-N′-(quinolin-2-ylmethyl)- ethylenediamine (L4, 4), and N-methyl-N,N′-bis(pyrid-2-ylmethyl)-N′- imidazole-2-ylmethyl)-ethylenediamine (L5, 5), has been isolated and characterized by means of elemental analysis, mass spectrometry, UV/Vis spectroscopy, and electrochemistry. The single-crystal X-ray structure of [Ni(L3)(CH3CN)](BPh4)2 reveals that the nickel(II) center is located in a distorted octahedral coordination geometry constituted by all the five nitrogen atoms of the pentadentate ligand and an acetonitrile molecule. In a dichloromethane/acetonitrile solvent mixture, all the complexes show ligand field bands in the visible region characteristic of an octahedral coordination geometry. They exhibit a one-electron oxidation corresponding to the NiII/NiIII redox couple the potential of which depends upon the ligand donor functionalities. The new complexes catalyze the oxidation of cyclohexane in the presence of m-CPBA as oxidant up to a turnover number of 530 with good alcohol selectivity (A/K, 7.1-10.6, A=alcohol, K=ketone). Upon replacing the pyridylmethyl arm in [Ni(L1)(CH 3CN)](BPh4)2 by the strongly σ-bonding but weakly π-bonding imidazolylmethyl arm as in [Ni(L5)(CH 3CN)](BPh4)2 or the sterically demanding 6-methylpyridylmethyl ([Ni(L3)(CH3CN)](BPh4)2 and the quinolylmethyl arms ([Ni(L4)(CH3CN)](BPh4) 2, both the catalytic activity and the selectivity decrease. DFT studies performed on cyclohexane oxidation by complexes 1 and 5 demonstrate the two spin-state reactivity for the high-spin [(N5)NiII-O.] intermediate (ts1hs, ts2doublet), which has a low-spin state located closely in energy to the high-spin state. The lower catalytic activity of complex 5 is mainly due to the formation of thermodynamically less accessible m-CPBA-coordinated precursor of [NiII(L5)(OOCOC 6H4Cl)]+ (5a). Adamantane is oxidized to 1-adamantanol, 2-adamantanol, and 2-adamantanone (3°/2°, 10.6-11.5), and cumene is selectively oxidized to 2-phenyl-2-propanol. The incorporation of sterically hindering pyridylmethyl and quinolylmethyl donor ligands around the NiII leads to a high 3°/2° bond selectivity for adamantane oxidation, which is in contrast to the lower cyclohexane oxidation activities of the complexes. Interesting, interesting! Nickel(II) complexes with a strong π-backbonding ligand act as efficient catalysts for the oxidation of alkanes (see figure, m-CPBA=m-chloroperbenzoic acid) by stabilizing the Ni-O. intermediate, whereas those with a better σ-donor ligand act as less efficient catalysts by destabilizing the reactive intermediate. The computed mechanism for cyclohexane hydroxylation reveals that a high-spin (S=3/2) [(L1/L5)NiII-O.]+ species is the ground state.
