eterotopic Bidentate Ligands and Their Roles in Catalysis – Mechanistic Approach to Reactions of Ethylene-Norbornene Copolymerization and Hydrogenation

第一部分 半惰性胺基-吡啶雙牙配位基之陽離子甲基鈀金屬錯合物化學式為{[R1HNCR2H (o-C6H5N)]Pd(Me)(NCMe)}(BF4) (R1 = 異丙基、第三丁基、苯基、2,6-二甲基苯基、2,6-二異丙基苯基；R2 = 氫、甲基)的形式。在溫和的條件下，此類有機金屬陽離子不需促進劑就能有效地催化乙烯與降冰片烯的共聚合反應，產物有高度的輪聚結構。這些平面四邊形甲基和降冰片烷基鈀金屬錯合物，存有快速且可逆的幾何異構化反應，而其幾何異構錯合物對單體的嵌入反應具有顯著不同的反應性。經由變溫核磁共振技術，乙烯嵌入、降冰片烯嵌入和幾何異構化反應的動力學測量已被詳細探討。在降冰片烯的嵌入反應中，快速的幾何異構化使得聚合鏈選擇在吡啶的鄰位，此結構亦是較穩定的熱力學產物。此外，降冰片烯嵌入反應的速率與降冰片烯濃度成正比，但乙烯嵌入反應卻與乙烯濃度無關。動力學的數據提供了乙烯/降冰片烯輪聚反應完整的機構。而DFT理論計算亦用來探討共聚合反應路徑，這兩個方法皆顯示出順式異構物，對單體具有較快的嵌入速度，輔以可逆的幾何異構化機制，完整的解釋輪聚共聚合反應及重要基本步驟的反應能量條件。 第二部分 亞碸-咪唑鹽類簡寫為[SO-imidazolium]+A-，經由其銀錯合物的金屬轉移反應，能成功的合成鈀金屬錯合物，由於亞碸的弱配位性，亞碸-氮雜環碳烯配位基簡寫為[SO-NHC]展現了半惰性及單牙基配位形式。[(SO-NHC)PdCl2]2其單牙碳烯基配位的形式，證實亞碸的弱配位性，兩性離子的亞碸-咪唑鈀金屬錯合物(SO-imidazolium)PdCl3亦被合成出來，證實咪唑鹽類的亞碸基形成單牙配位。在溶液中，亞碸基離去而形成兩性離子的(SO-imidazolium)2PdCl4錯合物，接續的去質子化反應，進而產生雙亞碸-氮雜環碳烯的鈀金屬錯合物，形成(SO-NHC)2PdCl2的反式結構。 亞碸-氮雜環碳烯的丙烯基鈀金屬錯合物以(SO-NHC)Pd(R-allyl)X (R = 氫、甲基、苯基；X = 氯、六氟磷酸)的形式也已成功的合成，並能有效的催化不飽和稀烴的氫化反應。核磁共振技術和X光結晶學確定其結構，皆顯示出碳烯配基與未修飾的丙烯基部分為鄰位結構，這些丙烯基鈀金屬錯合物具有內與外異構物，由於碳烯的強反式效應，內外異構物能經由η3-η1-η3的異構化反應而互相轉換，在變溫核磁共振光譜中，由於五圓環骨架的環翻轉被低溫所限制，內與外異構物會分別分裂出一組非鏡像異構物，而其環翻轉能量約為12.4 - 13.5 kcal/mol。Part I Cationic methylpalladium complexes with hemilabile heterotopic bidentate ligands of α-amino-pyridines, in the formula of {[R1HNCR2H(o-C6H5N)]Pd(Me)(NCMe)}(BF4) (R1 = iPr, tBu, Ph, 2,6-Me2C6H3, 2,6-iPr2C6H3 R2= H, Me), have been found to be effective precursors for catalytic copolymerization of ethylene (E) and norbornene (N) under mild conditions. Both of the square planar methyl and norbornyl palladium(II) complexes exhibit facile reversible geometrical isomerization. The geometric isomers show distinct reactivity toward olefin-insertion reactions. Detailed kinetic studies by means of variable-temperature NMR technique on ethylene-insertion, norbornene-insertion, as well as the geometric isomerization have been examined. Corresponding DFT calculations for such fundamental paths have also been investigated. Both approaches reveal consistent results, indicating that the cis-isomers undergo olefin insertion more facile than the trans-isomers. An unprecedented mechanism in which the reversible geometric isomerization and the geometric isomer-distinguished kinetics lead to the alternating E-N copolymerization will be presented. Part II The sulfoxide(SO)-imidazolium salts have been successfully synthesized to react with palladium precursors via transmetallation of resulting silver complexes. The SO-NHC ligand behaving like monodentate results in the formation of dinuclear species in the formula of [(SO-NHC)PdCl2]2. The zwitterionic (SO-imidazolium)PdCl3 complex with the configuration of coordinated sulfoxide was also synthesized. Subsequent deprotonation afforded the trans-(SO-NHC)2PdCl2 complex, which was resulted from the transformation to unusual anionic PdCl4 complex bearing two SO-imidazolium zwitterions in solvents. A series of (SO-NHC)Pd(R-allyl)X (R = H, Me, Ph and X = Cl, PF6) complexes have been found to be effective catalysts for alkene hydrogenation. These complexes revealing cis configuration of NHC and unsubstituted allylic group were characterized by the NMR techniques and X-ray crystallography. A rapid exo-endo exchange of allyl group via η3-η1-η3 isomerization was observed. In variable-temperature 1H NMR spectrometry, the envelope movement of five-membered metallacyclic structure of [(SO-NHC)Pd(allyl)]PF6 complex affords four exo- and endo- diastereomers. The energy of such fluxion was also examined to give the ΔG‡ in the range of 12.4 - 13.5 kcal/mol