Cobalt-based molecular electrocatalysis of nitrile reduction: evolving sustainability beyond hydrogen

Two new cobalt bis-iminopyridines, [Co(DDP)(H2O)2](NO3)2 (1, DDP = cis-[1,3-bis(2-pyridinylenamine)] cyclohexane) and [Co(cis-DDOP)(NO3)](NO3) (2, cis-DDOP = cis-3,5-bis[(2- Pyridinyleneamin]-trans-hydroxycyclohexane) electrocatalyse the 4-proton, 4-electron reduction of acetonitrile to ethylamine. For 1, this reduction occurs in preference to reduction of protons to H2. A coordinating hydroxyl proton relay in 2 reduces the yield of ethylamine and biases the catalytic system back towards H2

Water Oxidation by Mononuclear Ruthenium Complex with a Pentadentate Isoquinoline-Bipyridyl Ligand

Mononuclear ruthenium complexes with a pentadentate ligand, N,N-bis[(isoquinolin-1-yl)methyl][6-(pyridin-2-yl)pyridin-2-yl]methanamine (DIQ-Bpy), were synthesized and characterized by 1H NMR spectroscopy, elemental analysis, electrochemistry, and theoretical calculations. The oxidation of water by [Ru(DIQ-Bpy)(H2O)]2+ was observed in the presence of excess amounts of CeIV. Relative to [Ru(DPA-Bpy)(H2O)]2+ [DPA-Bpy = N,N-bis(2-pyridinylmethyl) -2,2-bipyridine-6-methanamine], the substitution of pyridine groups in DPA-Bpy with electron-withdrawing isoquinolines results in higher redox potential and lower activity for the oxidation of water by [Ru(DIQ-Bpy)(H2O)] 2+. A kinetic study of water oxidation by [Ru(DPA-Bpy)(H 2O)]2+ suggests a mononuclear pathway for the oxidation of water. The noncovalent interaction between isoquinoline groups in [Ru(DIQ-Bpy)(H2O)]2+, which favors the formation of dinuclear species, might account for the lower activity for water oxidation by [Ru(DIQ-Bpy)(H2O)]2+. Mononuclear Ru complexes with a pentadentate ligand, N,N-bis[(isoquinolin-1-yl)methyl][6-(pyridin-2-yl)pyridin- 2-yl]methanamine (DIQ-Bpy), were synthesized and characterized. The effects of isoquinoline groups on the electrochemistry and the activity of [Ru(DIQ-Bpy)(H2O)]2+ on water oxidation are discussed. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Electronic effects on a mononuclear Co complex with a pentadentate ligand for catalytic H2 evolution

Previous studies of Co catalysts for H2 evolution have shown opposite effects between the redox potentials of Co centers and their catalytic properties such as the overpotential and turnover frequency: Co catalysts with more positive reduction potentials from structural modification display insignificant changes in the overpotential for H2 evolution and require stronger acid for catalysis, and Co catalysts with lower overpotentials show decreased turnover frequency for H2 evolution. In order to explore the electronic effects of a ligand scaffold on the catalytic properties for H2 evolution by a Co complex with a pentadentate ligand, N,N-bis(2-pyridinylmethyl)-2,2′-bipyridine-6-methanamine (DPA-Bpy), we replaced the pyridyls in DPA-Bpy with more basic isoquinoline groups. In contrast to data from previously reported studies, in the current study, a Co complex with a more positive reduction potential, resulting from the replacement of pyridyls with isoquinoline groups, leads to a lower overpotential and higher turnover frequency for both electro- and photocatalytic H2 production in neutral aqueous solution

Electronic Effects on a Mononuclear Co Complex with a Pentadentate Ligand for Catalytic H₂ Evolution

Previous studies of Co catalysts for H₂ evolution have shown opposite effects between the redox potentials of Co centers and their catalytic properties such as the overpotential and turnover frequency: Co catalysts with more positive reduction potentials from structural modification display insignificant changes in the overpotential for H₂ evolution and require stronger acid for catalysis, and Co catalysts with lower overpotentials show decreased turnover frequency for H₂ evolution. In order to explore the electronic effects of a ligand scaffold on the catalytic properties for H₂ evolution by a Co complex with a pentadentate ligand, <i>N</i>,<i>N</i>-bis­(2-pyridinylmethyl)-2,2′-bipyridine-6-methanamine (DPA-Bpy), we replaced the pyridyls in DPA-Bpy with more basic isoquinoline groups. In contrast to data from previously reported studies, in the current study, a Co complex with a more positive reduction potential, resulting from the replacement of pyridyls with isoquinoline groups, leads to a lower overpotential and higher turnover frequency for both electro- and photocatalytic H₂ production in neutral aqueous solution

Spectroscopy, Structure, Biomacromolecular Interactions, and Antiproliferation Activity of a Fe(II) Complex With DPA-Bpy as Pentadentate Ligand

An Fe(II) complex with DPA-Bpy (DPA-Bpy = N,N-bis(2-pyridinylmethyl)-2,20-bipyridine-6 -methanamine) as the ligand was synthesized and characterized to mimic bleomycin. The binding constants ( ) of the complex with calf thymus DNA and human serum albumin (HSA) were quantitatively evaluated using fluorescence spectroscopy, with as 5.53×10 and 2.40×10 M, respectively; the number of the average binding site () is close to 1. The thermodynamic analyses suggested that the electrostatic interactions exist between the complex and DNA, and the hydrogen bonding and Van der Waals force exist for the complex and HSA. The Fe complex exhibits cleavage ability toward pBR322 DNA, and the crystal structure of the HSA Fe complex adduct at 2.4 Å resolution clearly shows that His288 serves as the axial ligand of the Fe center complexed with a pentadentate DPA-Bpy ligand. Furthermore, the cytotoxicity of the complex was evaluated against HeLa cells. Both the Fe complex and HSA Fe complex adduct show obvious effect on cell proliferation with an IC of 1.18 and 0.82 μM, respectively; they induced cell apoptosis and arrested cell cycles at S phase. This study provides insight into the plausible mechanism underlying their metabolism and pharmacological activity

Efficient Photocatalytic Water Reduction Using In Situ Generated Knölker's Iron Complexes

Inâ situ generated ironâ based Knölker complexes were found to be efficient catalysts in a fully nonâ noble metal Cuâ Fe photocatalytic water reduction system. These mononuclear iron catalysts were able to generate hydrogen up to 15 times faster than previously reported [Fe3(CO)12]. A reductive quenching mechanism was shown to operate by fluorescence experiments.Photo finish: Inâ situ generated ironâ based Knölker complexes are efficient catalysts in a fully nonâ noble metal Cuâ Fe photocatalytic water reduction system. These mononuclear iron catalysts generate hydrogen up to 15 times faster than previously reported [Fe3(CO)12]. A reductive quenching mechanism is shown to operate by fluorescence experiments. CuPS=copper(I) photosensitizer; SR=sacrificial reductant.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137356/1/cctc201600186.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137356/2/cctc201600186_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137356/3/cctc201600186-sup-0001-misc_information.pd