| dc.description.abstract | Using meso-tetrakis(pentafluorophenyl) N-confused porphyrin (NCTPFPP ) (1) as a ligand, CoII(HCTPFPP) (1a) was firstly synthesized and characterized by UV-vis spectrometer, 1H-NMR spectroscopy, EPR spectroscopy, and cyclic voltammetry. The spectroscopic data confirmed that Co(HCTPFPP) is Co(II). The electron withdrawing meso-substituents of 1a, shifted the first redox wave toward positive (22mV more positive in comparision with the first oxidation potential in Co(HCTPP) )and lower the energy level of HOMO, resulted in a 16% slower in reducing the oxidation rate compared with phenyl substitued CoII(HCTPP).
Besides cobalt complex, three new types of nickel N-confused porphyrin complex analogues, Ni(3-CNHCTPP) (3a), Ni(HCTPFPP) (1c) and Ni(HCTPFPOP) (4a) were also prepared and characterized by UV-vis spectrometer, 1H-NMR pectroscopy, cyclic voltammetry, and single crystal X-Ray structure determinations.
From the results of cyclic voltammetry, we found that the C≡N α position substitued- nickel N-confused porphyrin has the most positive oxidation potential with the potential close to the value in meso-pentapluoro phenyl substitued-nickel N-confused porphyrin. As for Ni(HCTPFPOP) (4a), which has three reversible oxidation processes, the first oxidation step occurs on a nickel ion centered molecular orbital as confirmed by spectroelectrochemical studies.
Besides, we demonstrate a new sandwich structure of nickel N-confused porphyrin complex, {[Ni(HCTPPH)·]2Ag}SbF6 (2), accroding to the result of EPR spectrum and 1H-NMR, we insist that (2) is Ni(II) radical spices. In addition, 2D-NMR spectra also show a singlet proton signal located at inner carbon of N-confused porphyrin ligand and confirms a dianionic NCP core under 2H tautomeric form.
We found that the replacement of meso-phenyl by meso-pentapluoro phenyl significantly increased the solubility and caused an anodic shift to the reduction waves. As electrocatalytic hydrogen evolution is closely correlated to the redox potential of catalysts, metalloporphyrins with strong electron-withdrawing substituents are considered to be able to reduce the energy inputs for generating H2, and thus lower the cost of hydrogen.Therefore, we use Ni(HCTPFPP) (1c) and Ni(HCTPFPOP) (4a) as the hydrogen-evolution-reaction (HER) catalyst. The results show that Ni(HCTPFPP) (1c) and Ni(HCTPFPOP) (4a) can catalyze H2 generation under electrochemical coditions in the presence of acetic acid or TFA as the exogeneous proton source, and Ni(HCTPFPOP) using TFA as proton source has the best HER reactivity with onset potential of 0.8V.
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