環內附加甲基吡啶碳氮異位紫質鐵{FeNO}7六配位一氧化氮錯合物研究

我們根據文獻的方法，在未添加任何強鹼性的試劑下，成功的在鎳金屬碳氮異位紫質中的環內碳加上了甲基吡啶取代基，並透過簡單的色層管柱分析獲得純化的產物Ni(CTPP-CH2Py) (1)，且此化合物也不會因為立體障礙的因素導致不穩定而降解。接著我們嘗試了不同濃度的鹽酸來脫除鎳金屬以獲得含有環內取代基的free base ligand: (CTPP-CH2Py)H2 (2)，發現加入一毫升33%濃度鹽酸具有最佳的產率，也間接地證明環內碳的取代基是非常穩定的，不會因為強酸的加入而脫除；上述的兩種化合物皆完成了一系列的光譜分析並獲得其晶體結構。1H NMR光譜中，在Ni(CTPP-CH2Py) (1)與(CTPP-CH2Py)H2 (2)相比之下發現由於配位路易氏酸，逆磁鎳錯合物Ni(CTPP-CH2Py) (1)中較去金屬配位基為downfield。另外，在去金屬反應後所得(CTPP-CH2Py)H2 (2)中，少了金屬的鍵結也使外翻pyrrole ring偏離平均平面，碳氮異位紫質的芳香性降低、環電流降低故遮蔽效應降低。接下來我們在(CTPP-CH2Py)H2 (2)中與FeBr2反應，獲得了Fe(HCTPP-CH2Py)Br (3)，並透過Fe(d20-HCTPP-CH2Py)Br的1H NMR光譜輔助了解此順磁化合物四個pyrrole ring 上之α-pyrrole及β-pyrrole氫原子訊號，也根據氫原子的化學位移推斷此化合物是屬於二價金屬鐵，與其他文獻類似順磁化合物相比之下，pyridine衍生基團的存在並不會使1H NMR上有太大的差異。透過了晶體的研究，Fe(HCTPP-CH2Py)Br (3)晶體是至今碳氮異位紫質環未出現過的堆積方式，為S型的方式堆積。最後，我們通過灌入一氧化氮氣體(NO)，由一系列光譜鑑定、DFT理論計算及晶體探討中證實獲得了異位紫質中第一個以衍生臂形式鍵結中心金屬鐵且穩定的六配位產物{FeNO}7，Fe(CTPP-CH2Py)NO (4)；其中，有趣的是在固態傅里葉轉換紅外光譜顯示了兩條一氧化氮(NO)吸收訊號分別為1660及1596 cm-1，而我們搭配了密度含泛理論計算(DFT Calculation)推測其為五配位及六配位一氧化氮ν(NO)的震動光譜訊號，因為軸配位pyridine的σ-donating造成trans-effect，N-O鍵結強度下降故六配位一氧化氮訊號為1596 cm-1，而此效應也被科學家認為是六配位{FeNO}n系統中主要影響Fe-NO、N-O鍵結鍵長之因子，且最後透過晶體的固態及液態IR光譜證實此化合物在溶劑中五、六配位具有一個平衡存在，也證實了理論計算的正確性。

關鍵字

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並列摘要

Without adding any strong alkaline reagent, we successfully appended a pyridine arm to the inner carbon of nickel N-confused porphyrin, and obtained the metal complex Ni(CTPP-CH2Py) (1). This nickel complex is air stable and can be purified through column chromatography. The desired free-base (CTPP-CH2Py)H2 (2) can then be isolated after demetallated by hydrochloric acid. 1H NMR spectroscopic studies revealed that, the proton signals of Ni( CTPP-CH2Py) (1) are more downfield shifted than free base due to nickel che-lation. The upfield-shifted protons signals for the β-pyrrolic protons on (CTPP-CH2Py)H2 (2) might be originated from the decreased ring current of free-base due to a more distorted porphyrin core in the absence of a central metal ion. Next, we used (CTPP-CH2Py)H2 (2) to react with FeBr2 to obtain Fe(HCTPP-CH2Py)Br (3). Compared with other paramagnetic iron(II) N-confused porphyrin complexs, the presence of pyridine does not cause a major difference on chemical shifts of 1H NMR. Examining the Fe(HCTPP-CH2Py)Br (3) crystal stacking, we identified an unprecedented S-type stacking linked by hydrogen bonding inter-actions. Finally, injecting nitric oxide gas into the Fe(HCTPP-CH2Py)Br (3), isolated a stable six-coordinated {FeNO}7 iron nitrosyl complex with an appended pyridine coordinated to the iron metal center, Fe(CTPP-CH2Py)NO (4). The compound 4 was characterized through a series of spectroscopic methods and DFT theoretical calculations including its crystal struc-ture. The Fourier-transform infrared spectroscopy (FTIR) shows two nitric oxide stretching frequencies at 1660 and 1596 cm-1. Combined with DFT calculation, we speculated that it is nitric oxide signals of five-coordinate and six-coordinated complex. The trans effect of σ-donating pyridine coordination would result a decreased N-O bond order and the 1596 cm-1 signal has been assigned as a signal from the six-coordinate iron complex.

並列關鍵字

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參考文獻

1. (a) Milgrom, L. R., The Colours of Life: An Introduction to the Chemistry of Porphyrins and Related Compounds. Oxford University Press., USA 1997.; (b) Dolphin, D., The Porphyrins. Academic Press: New York 1998.

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