含硫醚-氮雜環碳烯配位基之有機鈀錯合物之合成、異構及催化

Synthesis and Catalysis of Thioethers-Functionalized N-Heterocyclic Carbene Palladium Complexes

王嘉慶(Chia-Ching Wang)

指導教授 ： 陳竹亭

國立臺灣大學/理學院/化學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.00612

摘要

本篇論文中主要合成五元環之硫醚-碳烯的鈀錯合物，探討其五、六元環的金屬環在配位化學上之差異、丙烯基鈀錯合物的異構及催化。
甲基-及乙基-為連結的硫醚-咪唑鹽類已被成功的合成與鑑定。此系列硫醚-咪唑鹽類與氧化銀作用所生成硫醚-碳烯之銀錯合物可再與鈀金屬前驅物進行金屬置換反應，得到(S-NHC)PdCl2形式的硫醚-碳烯之鈀錯合物。(S-NHC)PdCl2錯合物可由甲基-連結的硫醚-碳烯構成五元環的金屬環錯合物，而此類錯合物可加入三苯基磷反應測定硫醚-碳烯配基對金屬鈀是否具有半惰性的性質。我們將五元環的金屬錯合物進行此反應，得到三苯基磷取代氯離子的陽離子產物，然而，此產物與文獻中的三苯基磷取代硫醚基之六元環產物不同。由此取代反應可得知六元環錯合物上的硫醚配位基具有半惰性的性質亦或五元環錯合物之配基具較六元環環錯合物之配基強的鉗合效應。
硫醚-氮雜環碳烯的丙烯基鈀錯合物以(S-NHC)Pd(allyl-R)X (R = 氫, 甲基, 苯基; X = 氯, 四氟硼酸, 六氟磷酸)的形式也已成功合成，並能有效的催化不飽和烯烴氫化反應。此類錯合物已用核磁共振技術及X光結晶學鑑定其結構，顯示出硫醚基與丙烯基之取代基在同方位之順式結構。從二維核磁共振技術中，發現此系列丙烯基鈀錯合物具有內與外異構物，由於氮雜環碳系具有強的反式效應，內外異構物可經由η3-η1-η3異構化或經由硫醚基的反轉彼此互相轉換。變溫核磁共振實驗中，求得η3-η1-η3異構化及硫醚基的反轉能量屏障。

關鍵字

氮雜環碳烯 ； 硫醚 ； 鈀 ； 丙烯基 ； 異構

並列摘要

The hemilability of six- and seven- membered ring metallacycle of thioether-functionalized NHC palladium complexes were observed in solution; therefore, the five-membered ring metallacycle complexes which were constituted by the methyl- tethered thioether-NHC lgands could also exhibit hemilabile behavior in solution.
The methyl- and ethyl-tethered thioether(S)-imidazolium salts have been successfully synthesized and employed to afford the N-heterocyclic carbene (NHC) silver derivatives as carbene precursors of transmetallation. The resulting (S-NHC)PdCl2 complexes constructing with five-membered palladacycles were characterized by NMR techniques and X-ray crystallography. The coordination of thioether group could be displaced by additional PPh3 indicative of the hemilability of S-NHC ligand. Unlike the ethyl-tethered (S-NHC)PdCl2 complex, the cationic methyl-tethered S-NHC palladium complex in the formula of [(S-NHC)Pd(PPh3)Cl]Cl was also accompanied in the reaction resulted from the stronger chelating effect of five-membered palladacycles.
A series of (S-NHC)Pd(allyl-R)X (R = H, Me, Ph and X = Cl, BF4, PF6) complexes has been synthesized and characterized by NMR spectroscopy and X-ray crystallography, which shows the cis configuration of the NHC and unsubstituted allylic groups in their square planar geometries. A rapid exo-endo exchange of the allylic group was observed via η3-η1-η3 isomerization in 2D NMR spectra, which was attributed to the strong trans influence of the carbene donor. The energy barriers of the η3-η1-η3 isomerization and the rapid inversion of sulfur atom were examined by variable-temperature NMR techniques. These S-NHC allylic palladium complexes were evaluated for the reaction of olefins hydrogenation showing comparable activities with literature reports.

並列關鍵字

N-Heterocyclic Carbene ； Thioether ； Palladium ； allyl ； Isomerization

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