Synthesis and Catalytic Activity of N-Heterocyclic Carbene Dinuclear Metal Complexes

在本篇論文中以雙金屬碳烯錯合物為主題，探討這類錯合物對催化反應的影響。在2,7-二氯萘啶修飾上2,4,6-三甲基咪唑鹽類，可得到7，其銀錯合物9與[Pd(PhCN)2Cl2]進行碳烯轉移反應，即得雙鈀錯合物10，其中碳烯以對位形式配位在鈀金屬上。此外，將[ClAu(Me2S)]與9反應，可合成出雙金錯合物11。另外，亦利用吡啶-咪唑鹽類8與[Pd2(dba)3]進行氧化加成反應，形成吡啶-碳烯雙芽配位的單鈀錯合物12。 雙金錯合物11對硫粉、三氟醋酸或三苯膦皆不進行反應，得知11之金屬-碳烯鍵結具有極高穩定性。對於硫、磷配基，甚至強酸的條件下，均無碳烯-金屬鍵結斷裂或取代的現象。並將其應用於路易斯酸催化縮酮水解，對5-(Hydroxymethyl)-2,2,5-trimethyl-1,3-dioxane反應物，八小時即可以完全反應。並將催化劑經回收使用測試，可以發現11仍具有催化活性。 將雙鈀錯合物10應用在Kumada偶合反應，選用4-溴甲氧苯與環己烷格林鈉試劑為模型反應。從結果觀察，使用單鈀錯合物12為催化劑，反應在二十四小時以上，轉換率只停留在32%，且主要為Beta-氫脫去產物與還原產物，只有少量的偶合產物；然而，使用雙鈀錯合物10，只需七小時反應即進行完全，其中有85% Kumada產物，伴隨13%環己烯之beta-氫脫去產物，推測原因可能是錯合物10結構中，配基上碳烯是以對位形式配位在鈀金屬，而減少beta-氫脫去反應的發生。對於一系列的芳香族或脂肪族之格林鈉試劑，與不同溴烷作用，亦做類似分析探討。Abstract In this thesis, we focused on the preparation of binuclear transition metal carbene complexes and the study of their catalytic activities. Modification of 2,7-dichloro-1,8- naphthyridine with N-mesityl imidazole yielded 7, which reacted with Ag2O to yield the corresponding silver complex 9. Treatment of 9 with [Pd(PhCN)2Cl2] in CH3CN provided the palladium complex 10. X-ray crystal structural analysis show that two NHC ligands are seated in trans positions around palladium center. In addition, treatment of 9 with [ClAu(Me2S)] yielded the corresponding Au(I) complexes 11. Oxidative addition of the C–H bond at 2-position of pyridinyl-imidazolium salt 8 with [Pd2(dba)3] generated the desired mono-carbene complex 12. Complex 11 appears to be fairly stable toward sulfur, trifluoroacetic acid and triphenylphosphine. Complex 11 can act as an acid-catalyst on the hydrolysis of ketal. In particular, 5-(Hydroxymethyl)-2,2,5-trimethyl-1,3-dioxane was completely hydrolyzed within 8 hours under mild conditions. Furthermore, complex 11 can be easily recycled with the similar catalytic activity. The use of complex 10 as a catalyst in Kumada coupling reactions were investigated. Reaction of 4-bromoanisole and cyclohexylmagnesium bromide catalyzed by 12 only provided cyclohexene and anisole. On the other hand, 85% cross coupling product was obtained with the use of 10 as the catalyst for the same reaction. The possible reason may due to the rigid arrangement of NHC ligand in structure 10. The naphthyridine-based system readily hinders the isomerization of NHC moieties at cis position, thus reduces the possibility of B-H elimination. A series of coupling reactions between a wide range of aromatic or aliphatic Gringnard reagents with various alkyl bromides were studied