釕錯合物催化含噻吩芳香丙炔醇之環化反應

Cyclization of Aromatic Propargyl Alcohol with Thiophene Group Yielding Naphthothiophene Aldehyde Catalyzed by Ruthenium Complex

蔡福源(Fu-Yuan Tsai)

指導教授 ： 林英智

國立臺灣大學/理學院/化學研究所/博士(2012年)

https://doi.org/10.6342/NTU.2012.00869

摘要

釕金屬錯化合物 (Cp(PPh3)2RuCl) 與含噻吩芳香丙炔醇(3-噻吩) 1a 在低溫下進行環化反應獲得金屬碳烯錯合物2a，2a為含硫的奈環，此環化反應所產生的碳—碳鍵主要是來自噻吩與被金屬活化之參鍵內的碳原子所形成。同樣的條件在室溫下反應，將會得到2a 與少量的釕金屬丙二烯錯化合物 3a，然而3a無法轉換成2a，因此，環化反應主要是經由釕金屬與炔基進行π配位而形成。
2a 與三乙基胺(NEt3)在氧氣下室溫反應可得高產率之含硫奈環帶有醛基之有機物4a以及ONEt3、OPPh3當溶劑為氯仿時可回收Cp(PPh3)2RuCl。此氧化反應，首先PPh3先游離形成一空位，氧氣分子進入此空配位，經金屬活化後再藉由NEt3奪取其一被活化之氧原子，形成未觀察到之 oxo-碳烯中間產物，最後 oxo 在與碳烯配基進行偶合反應形成 4a 以及Cp(PPh3)2RuCl 在氯仿溶劑中。然而在含有甲醇的溶劑中反應，除了可以得到 4a 之外還可以得到 5a-1酯類有機物帶有OMe取代基。當釕金屬改變成Cp(dppf)RuCl與含噻吩芳香丙炔醇 1a反應其結果與使用釕金屬錯化合物 (Cp(PPh3)2RuCl)類似。很幸運的我們有得到碳烯錯合物 2a’以及有機物 4a，5a-1 的晶體。此外我們也合成含噻吩芳香丙炔醇(2-噻吩) 1b 與釕金屬錯合物反應也可以得到碳烯錯合物。經氧化後也可得到高產率之含醛基4b與酯基5b的有機物。在第一部分的最後我們也嘗試了一些碳烯錯合物，其一為高共軛長碳鍊以及無共軛之五環碳烯錯合物，加入NEt3在氧氣下室溫，並未反應，因此我們假設此系統需要兩個或兩個以上之芳香環方可進行。
第二部分中，我們將起始金屬置換成Cp(dppe)RuCl，將此金屬以1/2莫耳的量與1a反應在50℃氧氣以及日光下12小時即可獲得含醛基有機物4a，此方法減少了反應步驟以及反應時間。其反應機制與第一部分相似，其環化反應更為容易進行，主要是因為其含磷配基為螯合性的雙牙基，其所形成之碳烯錯合物2a”之夾角為82∘相較於錯合物2’之夾角97.9∘小了許多，因此降低了立體效應，讓噻吩更容易靠近被活化的三鍵形成環化產物。與第一部分不同的地方，主要在於dppe扮演了三乙基胺的角色，dppe上的磷原子不只需要空出一空配位，並且也扮演著攻擊被金屬活化之氧分子，形成OPPh2，而獲得4a。此氧化過程中金屬碳烯鍵會因為照光的關係使金屬碳烯鍵弱化，我們運用得高斯09軟體進行DFT的計算，計算出分子的相對能量與軌域組成，結果發現在LUMO(L)中金屬碳烯鍵有明顯的反鍵結軌域性質，在HOMOs(Hs)中也有觀察到明顯金屬碳烯鍵的鍵結軌域性質。此HOMO至LUMO的能量差為3eV(實驗值為2.8eV)，而H至H-3其能量接近，因此光線約在可見光區，當激發Hs上的電子躍遷至L時將造成碳烯鍵弱化。當溶劑換成醇類，此時將會得到5a酯類有機物，接著OPPh2以及1a在配位回金屬中心進行下一次環化/氧化等反應。然而在1b與金屬反應中，除了得到4b、5b之外還獲得縮醛產物8b。以1a為反應物時並未獲得縮醛產物，主要是因為過程中4a之氧與硫原子皆可配位在金屬上形成金屬六環，而硫原子的配位能力強於氧原子，因此造成金屬誘導羰基的能力下降，因而未能產生縮醛產物。除了含噻吩1a、1b之外我們還設計了含烯基1c或是呋喃配基1d、1e，與金屬進行反應皆可進行相同的反應。

關鍵字

釕金屬 ； 噻吩 ； 呋喃 ； 環化 ； 氧化

並列摘要

Chapter 1. The chemical reactions of Cp(PPh3)2RuCl with the phenyl propargylic alcohol 1a, bearing a 3-thiophene group are explored. The carbene complex 2a, obtained exclusively from this reaction at low temperature, contains the naphthothiophene group formed via a new cyclization process between the thiophene group and the inner carbon of the triple bond. Details of this process are revealed by running the reaction at room temperature, affording the allenylidene complex 3a as a side product. Complex 3a is not converted to 2a, indicating that the cyclization takes place while the triple bond is π-coordinated to the metal center. Complex 2a reacts with oxygen in the presence of NEt3 at room temperature to afford in high yield the naphthothiophene aldehyde 4a, ONEt3, OPPh3 and Cp(PPh3)2RuCl. Molecular O2 is likely activated by coordination to the metal center when one of the phosphine ligands dissociates. Then NEt3 promotes the oxygenation process by reacting with the coordinated O2 to afford ONEt3 and possibly an unobserved oxo-carbene complex. Coupling of the oxo and carbene ligands then yields 4a and Cp(PPh3)2RuCl in CHCl3. In a solvent system containing MeOH, the oxygenation reaction affords a mixture of 4a and the naphthothiophene ester compound 5a-1. The reactions of Cp(dppf)RuCl (dppf = 1,1'-bis(diphenyl-phosphino)ferrocene) with 1a, also afford the carbene complex 2a’ and 4a, 5a, which are characterized by X-ray diffraction analysis. For the phenyl propargylic alcohols 1b with a 2-thiophene substituent, different naphthothiophene aldehyde and ester compounds are also obtained in high yields via similar cyclization process followed by oxygenation under mild conditions.
Chapter 2.Five phenyl propargylic alcohols 1a-e, each containing either a heterocyclic group or an olefinic chain on the phenyl ring are prepared. In the presence of visible light, treatment of 1a with half equivalent of [Ru”]Cl ([Ru”] = CpRu(dppe)) and NH4PF6 under O2 at 50°C in THF for 12 hours affords aldehyde compound 4a in high yields. The other aldehydes 4b-e are similarly prepared from 1b-e, respectively. Formation of these aldehydes proceeds via a cyclization giving the carbene complex 2, which is isolated from stoichiometric reaction, followed by a facile oxygenation by O2 to give the final product. The cyclization forms a new C-C bond between the inner carbon of the triple bond and the unsaturated functional group of the heterocyclic ring. Oxygenation of 2 generating 4 is accompanied with formation of phosphine oxide of dppe. Oxygen activation possibly proceeds by coordination to the ruthenium center when one of the PPh2 of the dppe ligand dissociates. Then, the tethering dppe ligand could better react with the coordinated oxygen nearby and conceivably generates an unobserved oxo-carbene complex with partially oxidized PPh2CH2CH2P(O)Ph2 ligand. Coupling of the oxo/carbene ligands then yields 4. Presumably this partially oxidized ligand continuously promotes cyclization/oxygenation of 1 to obtain the second aldehyde 4. In a solvent system containing alcohol such as MeOH or EtOH, oxygenation reaction affords a mixture aldehyde 4 and the corresponding ester 5, and in some cases, generates acetal 8. Two carbene complexes 2a” and 2b” have been characterized by X-ray diffraction analyses. The UV-vis spectra of 2a” and 2b” consist of visible absorption bands with high extinction coefficient. From DFT theoretical calculations on 2a” and 2b”, the visible light is found to populate the LUMO anti-bonding orbital of mainly Ru=C bond, therefore, weakening the Ru=C bond in the oxygenation/demetalation reactions of 2.

並列關鍵字

Ruthenium ； cyclization ； thiophene ； propargylic alcohol ； fused-ring systems ； Cyclization ； ruthenium carbene complex ； oxygenation ； fused-ring systems ； DFT calculation

參考文獻

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