鈀-NHC配合物

有機金屬化學領域，鈀-NHC配合物是一類有機鈀化合物，其中鈀與N-雜環卡賓（NHC）形成配合物。它們在均相催化中的應用， ^[4]特別是交叉偶聯反應得到了研究。 ^[1] ^[4] ^[5]

合成

鈀-NHC配合物的合成遵循合成過渡金屬NHC配合物的方法，也可以通過取代Pd-L配合物中的不穩定配體L實現。不穩定的配體包括環辛二烯、二亞苄基丙酮、橋接鹵化物或膦。該過程可以與游離卡賓的原位生成結合使用。 Pd-NHC 配合物也可以通過與銀-NHC配合物的金屬轉移來合成。轉金屬化的NHC可以被分離出來用於隨後以兩步法與鈀反應，也可以在鈀存在下通過一鍋法反應合成。然而，通過銀金屬轉移生成Pd-NHC配合物成本高昂，並且受到銀配合物的光敏性的阻礙。 ^[4]

催化交叉偶聯中的鈀-NHC配合物

通過使用 N-雜環卡賓配體增強鈀催化的交叉偶聯反應的效果。鈀-NHC配合物已被證明在鈴木反應、根岸偶聯反應、薗頭耦合反應、熊田偶聯反應、檜山偶聯反應和施蒂勒反應中的作用。與相應的鈀-膦催化劑相比，鈀-NHC催化劑更快，並且適用更廣泛的底物範圍，具有更高的周轉數。 ^[4]

鈴木交叉偶聯

在Suzuki-Miyaura 交叉偶聯中，傳統的偶聯物是有機溴化物和有機硼化合物。反應通常使用有機溴化物作為偶聯劑，但有機氯化物成本較低，但是C-Cl鍵反應緩慢成為問題，隨着鈀-NHC配合物的出現，有機氯化物已成為Suzuki-Miyaura交叉偶聯的可行偶聯劑。 ^[4]^[6]

根岸偶聯

在根岸偶聯中使用NHC-鈀-PEPPSI複合物可以實現高周轉次數和周轉頻率。 ^[7]此外，NHC-鈀複合物可將sp3中心與sp3中心偶聯，產率高於無NHC的鈀類似物。 ^[8]然而，儘管如此，目前仍缺乏對鈀-NHC配合物及其在根岸偶聯中作用的研究。 ^[4]

薗頭耦合反應

用於薗頭耦合反應的鈀-NHC配合物具有交叉偶聯作用的溫度穩定性。 ^[9]與其他鈀-NHC介導的交叉偶聯反應一樣，使用鈀-NHC複合物也具有更高的周轉數。 ^[10]NHC-鈀環允許進行無銅的薗頭反應。 ^[11] ^[12]

赫克反應

在赫克交叉偶聯中使用鈀-NHC配合物可以與更便宜、供應充足的芳基氯底物反應。 ^[4]此外，通過調整咪唑環上的1,3取代基，可以提高催化劑在偶聯中的活性和穩定性。 ^[13]

參考

^ ^1.0 ^1.1 Marion, Nicolas; Navarro, Oscar; Mei, Jianguo; Stevens, Edwin D.; Scott, Natalie M.; Nolan, Steven P. Modified (NHC)Pd(allyl)Cl (NHC = N-Heterocyclic Carbene) Complexes for Room-Temperature Suzuki−Miyaura and Buchwald−Hartwig Reactions. Journal of the American Chemical Society. March 2006, 128 (12): 4101–4111. PMID 16551119. doi:10.1021/ja057704z.
^ Viciu, Mihai S.; Navarro, Oscar; Germaneau, Romain F.; Kelly, Roy A.; Sommer, William; Marion, Nicolas; Stevens, Edwin D.; Cavallo, Luigi; Nolan, Steven P. Synthetic and Structural Studies of (NHC)Pd(allyl)Cl Complexes (NHC = N-heterocyclic carbene). Organometallics. March 2004, 23 (7): 1629–1635. doi:10.1021/om034319e.
^ NHC-based Palladium Catalysts. Sigma-Aldrich. [24 October 2017]. （原始內容存檔於2020-08-13）（英語）.
^ ^4.0 ^4.1 ^4.2 ^4.3 ^4.4 ^4.5 ^4.6 Fortman, George; Nolan, Steven. N-Heterocyclic carbene (NHC) ligands and palladium in homogeneous cross-coupling catalysis: a perfect union. Chemical Society Reviews. 2011, 40 (10): 5151–5169. PMID 21731956. doi:10.1039/C1CS15088J.
^ Eastman, K. N-Heterocyclic Carbenes (NHCs) (PDF). www.scripps.edu. [2022-02-26]. （原始內容 (PDF)存檔於2022-01-22）.
^ Gstöttmayr, Christian; Volker, Böhm; Eberhardt, Herdtweck; Grosche, Manja; Herrmann, Wolfgang. A Defined N-Heterocyclic Carbene Complex for the Palladium-Catalyzed Suzuki Cross- Coupling of Aryl Chlorides at Ambient Temperatures. Angewandte Chemie International Edition. 2002, 41 (8): 1363–1365. doi:10.1002/1521-3773(20020415)41:8<1363::aid-anie1363>3.0.co;2-g.
^ Nasielski, J.; Hadei, N.; Achonduh, G; E. A. B., Kantchev; O'Brien, C.J. Structure–Activity Relationship Analysis of Pd–PEPPSI Complexes in Cross-Couplings: A Close Inspection of the Catalytic Cycle and the Precatalyst Activation Model. Chemistry: A European Journal. 2010, 16 (35): 10844–10853. PMID 20665575. doi:10.1002/chem.201000138.
^ Niloufar, Hadei; Kantchev, Eric; O'Brien, Christopher. The First Negishi Cross-Coupling Reaction of Two Alkyl Centers Utilizing aPd − N-Heterocyclic Carbene (NHC) Catalyst. Organic Letters. 2005, 7 (17): 3805–3807. PMID 16092880. doi:10.1021/ol0514909.
^ Batey, Robert; Shen, Ming; Lough, Alan. Carbamoyl-Substituted N-Heterocyclic Carbene Complexes of Palladium(II): Application to Sonogashira Cross-Coupling Reactions. Organic Letters. 2002, 14 (9): 1411–1414. doi:10.1021/ol017245g.
^ Kim, Jong-Ho; Lee, Dong-Ho; Jun, Bong-Hyun; Lee, Yoon-Sik. Copper-free Sonogashira cross-coupling reaction catalyzed by polymer-supported N-heterocyclic carbene palladium complex. Tetrahedron Letters. 2007, 48 (40): 7079–7084. doi:10.1016/j.tetlet.2007.08.015.
^ Chinchilla, Rafael; Nàjera, Carmen. The Sonogashira Reaction: A Booming Methodology in Synthetic Organic Chemistry. Chemical Reviews. 2007, 107 (3): 874–922. PMID 17305399. doi:10.1021/cr050992x.
^ McGuinness, David; Cavell, Kingsley. Donor-Functionalized Heterocyclic Carbene Complexes of Palladium(II): Efficient Catalysts for C - C Coupling Reactions. Organometallics. 2000, 19 (5): 741–748. doi:10.1021/om990776c.
^ Taige, Maria; Zeller, Alexander; Ahrens, Sebastian; Goutal, Sigrid; Hardtweck, Eberhardt. New Pd–NHC-complexes for the Mizoroki–Heck reaction. Journal of Organometallic Chemistry. 2006, 692 (7): 1519–1529. doi:10.1016/j.jorganchem.2006.11.050.

[Marion1-1] 1.0 ^1.1 Marion, Nicolas; Navarro, Oscar; Mei, Jianguo; Stevens, Edwin D.; Scott, Natalie M.; Nolan, Steven P. Modified (NHC)Pd(allyl)Cl (NHC = N-Heterocyclic Carbene) Complexes for Room-Temperature Suzuki−Miyaura and Buchwald−Hartwig Reactions. Journal of the American Chemical Society. March 2006, 128 (12): 4101–4111. PMID 16551119. doi:10.1021/ja057704z.

[2] Viciu, Mihai S.; Navarro, Oscar; Germaneau, Romain F.; Kelly, Roy A.; Sommer, William; Marion, Nicolas; Stevens, Edwin D.; Cavallo, Luigi; Nolan, Steven P. Synthetic and Structural Studies of (NHC)Pd(allyl)Cl Complexes (NHC = N-heterocyclic carbene). Organometallics. March 2004, 23 (7): 1629–1635. doi:10.1021/om034319e.

[3] NHC-based Palladium Catalysts. Sigma-Aldrich. [24 October 2017]. （原始內容存檔於2020-08-13）（英語）.

[review-4] 4.0 ^4.1 ^4.2 ^4.3 ^4.4 ^4.5 ^4.6 Fortman, George; Nolan, Steven. N-Heterocyclic carbene (NHC) ligands and palladium in homogeneous cross-coupling catalysis: a perfect union. Chemical Society Reviews. 2011, 40 (10): 5151–5169. PMID 21731956. doi:10.1039/C1CS15088J.

[eastman-5] Eastman, K. N-Heterocyclic Carbenes (NHCs) (PDF). www.scripps.edu. [2022-02-26]. （原始內容 (PDF)存檔於2022-01-22）.

[6] Gstöttmayr, Christian; Volker, Böhm; Eberhardt, Herdtweck; Grosche, Manja; Herrmann, Wolfgang. A Defined N-Heterocyclic Carbene Complex for the Palladium-Catalyzed Suzuki Cross- Coupling of Aryl Chlorides at Ambient Temperatures. Angewandte Chemie International Edition. 2002, 41 (8): 1363–1365. doi:10.1002/1521-3773(20020415)41:8<1363::aid-anie1363>3.0.co;2-g.

[7] Nasielski, J.; Hadei, N.; Achonduh, G; E. A. B., Kantchev; O'Brien, C.J. Structure–Activity Relationship Analysis of Pd–PEPPSI Complexes in Cross-Couplings: A Close Inspection of the Catalytic Cycle and the Precatalyst Activation Model. Chemistry: A European Journal. 2010, 16 (35): 10844–10853. PMID 20665575. doi:10.1002/chem.201000138.

[8] Niloufar, Hadei; Kantchev, Eric; O'Brien, Christopher. The First Negishi Cross-Coupling Reaction of Two Alkyl Centers Utilizing aPd − N-Heterocyclic Carbene (NHC) Catalyst. Organic Letters. 2005, 7 (17): 3805–3807. PMID 16092880. doi:10.1021/ol0514909.

[9] Batey, Robert; Shen, Ming; Lough, Alan. Carbamoyl-Substituted N-Heterocyclic Carbene Complexes of Palladium(II): Application to Sonogashira Cross-Coupling Reactions. Organic Letters. 2002, 14 (9): 1411–1414. doi:10.1021/ol017245g.

[10] Kim, Jong-Ho; Lee, Dong-Ho; Jun, Bong-Hyun; Lee, Yoon-Sik. Copper-free Sonogashira cross-coupling reaction catalyzed by polymer-supported N-heterocyclic carbene palladium complex. Tetrahedron Letters. 2007, 48 (40): 7079–7084. doi:10.1016/j.tetlet.2007.08.015.

[11] Chinchilla, Rafael; Nàjera, Carmen. The Sonogashira Reaction: A Booming Methodology in Synthetic Organic Chemistry. Chemical Reviews. 2007, 107 (3): 874–922. PMID 17305399. doi:10.1021/cr050992x.

[12] McGuinness, David; Cavell, Kingsley. Donor-Functionalized Heterocyclic Carbene Complexes of Palladium(II): Efficient Catalysts for C - C Coupling Reactions. Organometallics. 2000, 19 (5): 741–748. doi:10.1021/om990776c.

[13] Taige, Maria; Zeller, Alexander; Ahrens, Sebastian; Goutal, Sigrid; Hardtweck, Eberhardt. New Pd–NHC-complexes for the Mizoroki–Heck reaction. Journal of Organometallic Chemistry. 2006, 692 (7): 1519–1529. doi:10.1016/j.jorganchem.2006.11.050.

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