透過您的圖書館登入
IP:34.200.248.66
  • 學位論文

鈷−氮碳異位紫質一氧化氮錯合物的合成與鑑定及其一氧化氮還原至氧化亞氮或氫氣產生反應的探討

Chemistry of Cobalt−Nitrosyl N-confused Porphyrins and Studies on Reduction of Nitric Oxide to Nitrous Oxide or Hydrogen Evolution Reaction

指導教授 : 廖文峯 洪政雄
若您是本文的作者,可授權文章由華藝線上圖書館中協助推廣。

摘要


合成的錯合物{Co(NO)}8 [Co(CTPPMe)(NO)] (1)及[Co(HCTPP)(NO)] (2)已完成IR、UV-Vis、1H、15N NMR以及單晶X-ray繞射鑑定。其中{Co(NO)}8是採用Enemark−Feltham來表示金屬中心d軌域及π*(NO)軌域上電子數總和。利用環伏電位量測(CV)及其搭配IR或UV-Vis光譜電化學了解錯合物1及2的氧化還原特性。IR及UV-Vis光譜電化學結果顯示錯合物1的氧化反應主要來自porphyrin-環為主的電子而還原則是發生在具有CoNO-單元特徵的電子軌域。錯合物2的氧化(CoNO-單元)、還原(porphyrin-環)反應發生的表現與錯合物1相反。IR及UV-Vis光譜電化學分別呈現1^0/−/0及2^0/+/0氧化還原過程的可逆性。此研究中值得注意的是錯合物1及2的還原反應在光譜電化學的IR光譜上並沒有發生明顯且快速的NO離去反應,這個結果與一般鈷的紫質一氧化氮錯合物在還原反應中發生NO迅速離去有所不同。另一個{Co(NO)}7錯合物[Co(CTPPO)(NO)] (3)進行CV及IR光譜電化學研究結果呈現與錯合物1相似的氧化(porphyrin-環)、還原(CoNO-單元)反應。由上述歸納出:鈷的氮碳異位紫質一氧化氮錯合物當發生CoNO-單元軌域特徵的氧化還原反應造成ν(NO)約改變100 cm−1,而發生以porphyrin-環特徵軌域的氧化還原反應則造成ν(NO)改變約35 cm−1。而且還原反應造成錯合物1的ν(NO) = 95 cm−1的改變是目前在{Co(NO)}8鈷的紫質及類紫質一氧化氮錯合物中所未曾觀測到的變化。 IR光譜電化學的結果顯示具有可能性可以單離化學還原{Co(NO)}8錯合物1及2的產物並進行其後續反應性的研究。目前已可以藉由Co(Cp*)2為還原劑還原錯合物1得到[Co(CTPPMe)(NO)][Co(Cp*)2] (4) (89.7%)並且完成鑑定。錯合物4是目前第一個具有{Co(NO)}9電子結構的鈷−一氧化氮的紫質錯合物。在質子存在下,錯合物4將質子還原成氫氣並且伴隨被氧化成錯合物1。錯合物2還原後加入質子的平行反應亦是產生氫氣並且回復成錯合物2。在質子溶劑(protic solvent)下,例如:水、甲醇、乙醇,都可以用來驅動錯合物4上的NO配子轉化成N2O。但是該策略並無法驅使錯合物2的還原產物產生N2O。再者,同為CoNO-單元軌域特徵還原的錯合物3在還原反應後加入甲醇也無法產生N2O,由此推測還原NO至N2O可能需要足夠電子密度及還原反應在適當與CoNO-單元相關的特徵軌域。 在N2O產生反應機制的研究中,利用IR光譜及ESI(−)質譜術追蹤反應過程發現:錯合物4在甲醇存在下會部分形成具有氫鍵作用力的分子(4···MeOH);而該分子再與錯合物4反應後在IR光譜出現1622 cm−1的訊號。再者,由ESI(−)質譜追蹤反應測量到具有含[N2O2]雙鈷的氮碳異位紫質的中間產物生成,而且其生成至消減的趨勢及改變時間皆與IR光譜上1622 cm−1訊號的變化一致。由此推測1622 cm−1訊號的來源可能是來自於含[N2O2]成分中間產物的ν(NO)。此NO轉化成N2O的反應,在還原劑及NO來源可供給的條件下可以至少進行五個循環並且沒有顯著N2O生成量的減少。

並列摘要


Complexes [Co(CTPPMe)(NO)] (1) and [Co(HCTPP)(NO)] (2) with an {Co(NO)}8, the Enemark−Feltham notation of the total number of electrons in the metal d and π*(NO) orbitals, electronic configuration were prepared and thoroughly characterized by IR, UV-Vis, 1H and 15N NMR spectra as well as single-crystal X-ray diffraction. Cyclic voltammetry (CV) and the combined infrared or UV-Vis spectroelectrochemistry (IR or UV-Vis SEC) were also applied to understand the redox chemistry of complexes 1 and 2. IR and UV-Vis SEC studies revealed a porphyrin-based and a CoNO-centered oxidations for 1^0/+ and 2^0/+, respectively. The investigations also indicated a porphyrin-based reduction for 1^0/− and a CoNO-centered reduction for 2^0/−. IR and UV-Vis SEC spectra also demonstrated such good CoNO-centered redox reversibility of 1^0/−/0 or 2^0/+/0 observed in the cyclic voltammogram. It is noteworthy that the reduction of complex 1 or 2 resulted in no facile denitrosylation that commonly occurs in the reduction of {Co(NO)}8 cobalt−nitrosyl porphyrins. Moreover, CV and IR SEC studies on the known {Co(NO)}7 [Co(CTPPO)(NO)] (3) showed a porphyin-based 1st oxidation and a CoNO-centered 1st reduction. Concluded IR SEC results of the cobalt−nitrosyl N-confused porphyrins suggested Δν(NO) ≈ 100 and 35 cm−1 for the CoNO-centered and the porphyrin-based redox processes, respectively. Significantly, the reduction of 1 caused the shift of ν(NO) as large as 95 cm−1 that was first observed in the reduction of {Co(NO)}8 cobalt−nitrosyl porphyrinoid compounds. Suggestive evidences of IR SEC intrigued us to isolate the products reduced by Co(Cp*)2 and examine the subsequent reactivity of the reduced products. Only the product [Co(CTPPMe)(NO)][Co(Cp*)2] (4) of the reduction reaction of 1 to was quantitatively (89.7%) isolated and successfully characterized. Complex 4, to our knowledge, is the first isolated {Co(NO)}9 cobalt−nitrosyl porphyrinoid complex. In the presence of a proton source (NH4PF6), H2(g) evolution occurred with the oxidation of complex 4 to 1. The parallel reaction to evolve H2(g) was also active as conducting NH4+ into the reduction reaction of complex 2 by Co(Cp*)2. We then serendipitously observed that the addition of methanol, ethanol, or water to the THF solution of 4 (protic solvent/THF, 1:1, v/v) stimulated the NO-to-N2O conversion. The strategy of using MeOH to trigger the conversion of NO-to-N2O, however, was not effective as using the reduced product of complex 2. Furthermore, reducing complex 3 to its {Co(NO)}8 state generated neither H2(g) nor N2O(g) in the presence of NH4+ and MeOH, suggesting not only the reduction site but also the electron-richness were demanded for converting the coordinating NO to N2O. Mechanistic insight into the N2O formation was provided by monitoring the whole reaction process of complex 4 and MeOH using IR spectroscopy and ESI(−) mass spectrometry. Complex 4 was NO-reduction-silent in neat THF, but was partially activated to a hydrogen-bonded species 4···MeOH in THF/MeOH (1:1, v/v). This species coupling with 4 transformed NO into N2O, which was fragmented from an [N2O2]-bridging intermediate. An intensified IR peak at 1622 cm−1 was ascribed to ν(NO) due to the formation of an [N2O2]-containing intermediate. Time-course ESI(−) mass spectra supported the presence of the dimeric [Co(NCP)]2(N2O2) intermediate. The observation that the mass signals of the corresponding dimeric fragments exhibited maximum intensity after the reaction had proceeded for approximately 30 min is consistent with the result that the intensity of the peak at 1622 cm−1 in the IR spectrum reached its plateau at 30 min. Five complete NO-to-N2O conversion cycles have been achieved without significant decreasing on the amount of N2O produced.

參考文獻


(141) Gardner, P. R.; Gardner, A. M.; Martin, L. A.; Salzman, A. L. Proc. Natl. Acad. Sci. U.S.A. 1998, 95, 10378.
(50) Srinivasan, A.; Toganoh, M.; Niino, T.; Osuka, A.; Furuta, H. Inorg. Chem. 2008, 47, 11305.
(99) Sayed, N.; Baskaran, P.; Ma, X.; van den Akker, F.; Beuve, A. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 12312.
(176) Hung, C.-H.; Peng, C.-H.; Shen, Y.-L.; Wang, S.-L.; Chuang, C.-H.; Lee, H. M. Eur. J. Inorg. Chem. 2008, 1196.
(46) Peng, C. C.; Yang, F.-A.; Chen, J.-H.; Wang, S.-S.; Tung, J.-Y. Polyhedron 2008, 27, 2309.

延伸閱讀