寡電子錳紫質之製備、電化學及光譜性質研究

Preparation, Electrochemical and Spectral Properties of Manganese N-Methyl-Pyridylethynyl Porphyrins

陳彥全(Yan-Chuan Chem)

指導教授 ： 林敬堯

國立暨南國際大學/科技學院/應用化學系/碩士(2007年)

摘要

我們之前已經成功地在 free-base 5,15-biphenylporphine 的 10 和 20（meso）位置接上一個或兩個 N-methyl-2、3 或 4-pyridylethynyl 取代基，合成出一系列新的無金屬寡電子紫質。現在我們進一步藉由這些無金屬寡電子紫質為基礎，在紫質中心鑲入錳金屬，合成出一系列錳紫質。由觀測這些錳紫質的紫外光-可見光光譜可以得知，各個取代基會使錳紫質的吸收光譜產生強度不一的紅位移。在三種取代基中，N- methyl-4-pyridylethynyl 取代基對紫質的吸收光譜會產生最大的影響。這些紫質在電化學研究中有明顯的還原電位變化，其中 N-methyl-2-pyridylethynyl 顯現出有最強的拉電子效應。從電化學以及光譜電化學的偵測結果，我們推論 Mn 0 的還原反應除了三價錳變為二價錳之外，還包含了一個紫質大環的還原，形成陰離子自由基（anion radical）；而 Mn 1 - Mn 6 則更進一步的表現出了第三個電子的還原。在Mn 2 與 Mn 6 上甚至還觀測到了第四個電子的還原，這些還原都顯示出了相當高的可逆性。各項測定結果顯示，在無金屬紫質中心鑲入錳金屬後，並不會大幅度地改變取代基對於紫質的影響。而溶於DMF後，會出現紫質中心錳金屬的自身還原反應。由於未接上取代基的Mn 0並不會有此種現象發生，所以我們推論這種反應是由 N-methyl-2、3 與 4-pyridylethynyl 取代基的拉電子效應所造成的。

關鍵字

寡電子錳紫質 ； 紫外光-可見光光譜 ； 電化學 ； 光譜電化學

並列摘要

We have previously studied a series of novel electron-deficient free-base porphyrins by attaching one or two N-methyl-2, 3, or 4-pyridylethynyl groups to the 10 and/or 20-meso positions of free-base 5,15-biphenyl porphine. In this thesis, a series of manganese(III) N-methyl-pyridylethynyl-5,15-biphenyl-porphines are prepared and studied. The UV-Visible spectra demonstrate significant absorption red-shifts of these manganese porphyrins upon attaching the electron-withdrawing substituents, and N-methyl-4- pyridylethynyl group has the strongest influence on the porphyrin absorptions. Electrochemical studies show significant changes in the reduction potentials of these porphyrins, and N-methyl-2-pyridylethynyl group is the strongest electron-withdrawing substituent in the series. Based on the results of electrochemical and spectro- electrochemical studies, we conclude that Mn 0 undergo two one-electron reductions. The first reduction is to reduce manganese(III) to manganese(II), the second reduction is to reduce the porphyrin-ring to it’s anion radical. In addition, Mn 1 - Mn 6 undergo the third electron reduction. Moveover, Mn 2 and Mn 6 exhibit the fourth reduction, and these reductions all display good reversibility. Finally, Mn 1 - Mn 6 partially self-reduces to manganese(II) complexs when dissolving in DMF. The self-reduction is likely due to the N-methyl-2, 3, or 4- pyridylethynyl groups, since Mn 0 shows no self-reduction in DMF.

並列關鍵字

electron-deficient manganese porphyrin ； UV-Visible ； electrochemistry ； spectro-electrochemistry

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